Neuroplasticity, alternatively termed neural plasticity or simply plasticity, denotes the capacity of neural networks within the brain to undergo modification through processes of growth and structural reorganization. This phenomenon describes the brain's inherent ability to reconfigure and establish new neural connections, thereby facilitating its adaptation and operation in manners distinct from its previous configurations. Such adaptive processes can be triggered by various factors, including the acquisition of novel skills, exposure to altered environmental conditions, recovery from physical injuries, or adjustments to sensory or cognitive impairments. This inherent adaptability underscores the brain's dynamic and continuously evolving character, persisting even throughout adulthood. These transformations encompass a spectrum of alterations, from the formation of new connections by individual neuron pathways to broader systemic adjustments such as cortical remapping or shifts in neural oscillation. Additional manifestations of neuroplasticity include homologous area adaptation, cross-modal reassignment, map expansion, and compensatory masquerade. Illustrative instances of neuroplasticity involve circuit and network modifications arising from the mastery of new abilities, the assimilation of information, environmental influences, pregnancy, caloric consumption, consistent practice or training, and psychological stressors.
Neuroplasticity, also known as neural plasticity or just plasticity, is the medium of neural networks in the brain to change through growth and reorganization. Neuroplasticity refers to the brain's ability to reorganize and rewire its neural connections, enabling it to adapt and function in ways that differ from its prior state. This process can occur in response to learning new skills, experiencing environmental changes, recovering from injuries, or adapting to sensory or cognitive deficits. Such adaptability highlights the dynamic and ever-evolving nature of the brain, even into adulthood. These changes range from individual neuron pathways making new connections, to systematic adjustments like cortical remapping or neural oscillation. Other forms of neuroplasticity include homologous area adaptation, cross modal reassignment, map expansion, and compensatory masquerade. Examples of neuroplasticity include circuit and network changes that result from learning a new ability, information acquisition, environmental influences, pregnancy, caloric intake, practice/training, and psychological stress.
Historically, neuroscientists posited that neuroplasticity was exclusively observable during childhood; however, investigations conducted in the latter half of the 20th century demonstrated that numerous cerebral functions retain plasticity into adulthood. Nevertheless, the developing brain typically displays a more pronounced degree of plasticity compared to the mature adult brain. Activity-dependent plasticity holds substantial significance for optimal development, cognitive processes such as learning and memory, and the recuperation following cerebral injury.
Historical Context
Etymology and Early Concepts
The concept of plasticity was initially introduced in the context of behavior by William James in his 1890 work, The Principles of Psychology. Within this text, the term characterized "a structure weak enough to yield to an influence, but strong enough not to yield all at once". The earliest documented use of the specific phrase neural plasticity is attributed to the Polish neuroscientist Jerzy Konorski.
Early evidence supporting neuroplasticity emerged from experiments conducted in 1793 by the Italian anatomist Michele Vincenzo Malacarne. He detailed studies involving pairs of animals, where one animal from each pair underwent extensive training over several years before both were subjected to dissection. Malacarne's observations revealed that the cerebellums of the trained animals were considerably larger than those of their untrained counterparts. Despite their significance, these findings were subsequently overlooked. Later, in 1890, William James, in The Principles of Psychology, advanced the concept that the brain and its functional capabilities are not immutable throughout adulthood; nevertheless, this proposition received limited attention. Consequently, until the 1970s, the prevailing scientific consensus among neuroscientists held that the brain's structural and functional organization remained essentially static across the adult lifespan.
During the early 1900s, when the brain was widely perceived as a nonrenewable organ, the eminent neuroscientist Santiago Ramón y Cajal employed the term 'neuronal plasticity' to characterize non-pathological structural alterations observed in adult brains. Drawing upon his seminal neuron doctrine, Cajal initially defined the neuron as the fundamental constituent of the nervous system, a concept that subsequently provided a crucial basis for the development of neural plasticity theory. While many neuroscientists restricted the application of 'plasticity' to explain the regenerative capabilities solely of the peripheral nervous system, Cajal extended its use. He specifically referenced his discoveries concerning degeneration and regeneration within the adult brain, a component of the central nervous system. This perspective generated considerable debate, with figures such as Walther Spielmeyer and Max Bielschowsky contending that the central nervous system lacked the capacity to generate new cells.
The application of the term has since become extensive:
Considering the fundamental significance of neuroplasticity, an external observer might reasonably presume the existence of a precise definition and a foundational, universal framework guiding contemporary and prospective hypotheses and experimental designs. Regrettably, this presumption is unfounded. Although numerous neuroscientists employ 'neuroplasticity' as an overarching descriptor, its interpretation varies considerably among researchers across diverse subfields... Consequently, a universally agreed-upon conceptual framework does not appear to exist.
Contemporary Research and Discoveries
In 1923, Karl Lashley's experiments on rhesus monkeys revealed alterations in neuronal pathways, which he interpreted as evidence of brain plasticity. However, despite these findings and other research indicating plasticity, the concept of neuroplasticity did not gain widespread acceptance among neuroscientists.
Drawing inspiration from Nicolas Rashevsky's work, McCulloch and Pitts introduced the artificial neuron in 1943, incorporating a learning rule that posited the formation of new synapses when neurons exhibit simultaneous firing. This principle was subsequently elaborated upon in The organization of behavior (Hebb, 1949) and is presently recognized as Hebbian learning.
In 1945, Justo Gonzalo's research into brain dynamics led him to conclude that, unlike the activity observed in projection areas, the "central" cortical mass—positioned approximately equidistant from visual, tactile, and auditory projection areas—functions as a "maneuvering mass." He characterized this central mass as relatively unspecific or multisensory, possessing the capability to enhance neural excitability and reorganize activity through plastic properties. As an initial illustration of adaptation, Gonzalo cited the ability to perceive upright images when wearing reversing glasses, as demonstrated in the Stratton experiment. Furthermore, he documented several firsthand cases of brain injuries where he observed dynamic and adaptive properties within their associated disorders, particularly in inverted perception disorder [pp 260–62 Vol. I (1945), p 696 Vol. II (1950)]. Gonzalo theorized that a sensory signal within a projection area initially presents as an inverted and constricted outline. This outline, he proposed, would be magnified by an increase in recruited cerebral mass and subsequently re-inverted in more central areas due to brain plasticity, following a pattern of spiral growth.
Marian Diamond, affiliated with the University of California, Berkeley, published the inaugural scientific evidence of anatomical brain plasticity in 1964.
Substantial additional evidence emerged during the 1960s and subsequent decades, notably contributed by researchers such as Paul Bach-y-Rita, Michael Merzenich in collaboration with Jon Kaas, and numerous other scientists. During this period, Peter Putnam and Robert W. Fuller proposed an early iteration of the computational theory of mind, building upon Hebb's work, in an effort to elucidate the mechanisms underlying neuroplasticity.
During the 1960s, Paul Bach-y-Rita developed a device, subsequently tested on a limited cohort of individuals. This apparatus featured a chair equipped with vibrating nubs designed to translate camera-captured images, thereby facilitating a form of vision through sensory substitution.
Research involving stroke recovery patients further substantiated the concept of neuroplasticity, demonstrating that intact brain regions could, in some instances, partially assume functions previously impaired by damage. Shepherd Ivory Franz conducted notable work within this domain.
Eleanor Maguire documented structural alterations in the hippocampus linked to the acquisition of spatial knowledge of London's layout among local taxi drivers. Her findings indicated a redistribution of grey matter in London taxi drivers when compared to control groups. This research on hippocampal plasticity garnered significant interest not only from the scientific community but also from the global public and media.
Michael Merzenich, a neuroscientist, has been a leading pioneer in the field of neuroplasticity for more than three decades. He has advanced some of "the most ambitious claims for the field – that brain exercises may be as useful as drugs to treat diseases as severe as schizophrenia – that plasticity exists from cradle to the grave, and that radical improvements in cognitive functioning – how we learn, think, perceive, and remember are possible even in the elderly." Merzenich's research was significantly influenced by a pivotal discovery made by David Hubel and Torsten Wiesel during their experiments with kittens. Their experiment entailed surgically closing one eye of a kitten and subsequently mapping its cortical brain activity. Hubel and Wiesel observed that the brain region associated with the occluded eye was not inactive, contrary to expectations. Instead, this area processed visual information originating from the open eye, suggesting "…as though the brain didn't want to waste any 'cortical real estate' and had found a way to rewire itself."
Initially, neuroplasticity was understood to be confined to the critical period; however, Merzenich posited that neuroplasticity extends beyond this critical developmental window. His initial observation of adult plasticity emerged during a postdoctoral study conducted with Clinton Woosley. Their experiment investigated cerebral changes following the transection and subsequent regeneration of a peripheral nerve. The researchers meticulously mapped the somatosensory cortex representations of the hand in monkey brains both prior to and following the surgical severance and reanastomosis of a peripheral nerve. Contrary to expectations of disorganization, the post-surgical cortical hand map exhibited near-normal organization. This finding constituted a significant scientific advancement. Merzenich contended, "If the brain map could normalize its structure in response to abnormal input, the prevailing view that we are born with a hardwired system had to be wrong. The brain had to be plastic." In recognition of his contributions, Merzenich was awarded the 2016 Kavli Prize in Neuroscience for "the discovery of mechanisms that allow experience and neural activity to remodel brain function."
Neurobiology
Various theories and hypotheses exist regarding the underlying biological processes that facilitate neuroplasticity. Fundamentally, this phenomenon is predicated on synaptic modifications and the dynamic alterations in interneuronal connections influenced by neuronal activity. It is broadly accepted that neuroplasticity manifests in diverse forms, arising from a multitude of cellular pathways. These pathways, predominantly signaling cascades, enable modifications in gene expression, which subsequently induce neuronal changes and, consequently, neuroplasticity.
Several additional factors are hypothesized to contribute to the biological mechanisms governing neural network reorganization within the brain. These factors encompass synaptic regulation through phosphorylation, the involvement of inflammation and inflammatory cytokines, specific proteins like Bcl-2 and neurotrophins, mitochondrial energy production, and acetylcholine.
JT Wall and J Xu have elucidated the mechanisms underpinning neuroplasticity. They propose that reorganization is not solely a cortical phenomenon but rather manifests across all levels of the processing hierarchy, thereby generating the observed topographical alterations in the cerebral cortex.
Types
In their edited volume "Toward a Theory of Neuroplasticity", Christopher Shaw and Jill McEachern assert that a comprehensive, overarching theory encompassing all frameworks and systems within neuroplasticity research has yet to be established. Nevertheless, researchers commonly define neuroplasticity as "the ability to make adaptive changes related to the structure and function of the nervous system." Consequently, discussions frequently distinguish between two primary categories: structural neuroplasticity and functional neuroplasticity.
Structural neuroplasticity
Structural plasticity is generally conceptualized as the brain's capacity to modify its neuronal connections. Illustrative examples of structural neuroplasticity include alterations in grey matter volume or synaptic efficacy within the brain. This form of neuroplasticity frequently examines the impact of diverse internal or external stimuli on the brain's anatomical restructuring. New neurons are continuously generated and incorporated into the central nervous system, a process associated with this category of neuroplasticity. Contemporary researchers employ various cross-sectional imaging modalities, such as magnetic resonance imaging (MRI) and computerized tomography (CT), to investigate structural changes in human brains. Within contemporary academia, structural neuroplasticity receives considerable research attention within the field of neuroscience. However, adult neurogenesis "has not been convincingly demonstrated in humans".
Functional neuroplasticity
Functional plasticity denotes the brain's capacity to modify and adjust the functional characteristics of neuronal networks. This phenomenon manifests through four recognized mechanisms:
- homologous area adaptation
- map expansion
- cross-model reassignment
- compensatory masquerade.
Homologous area adaptation
Homologous area adaptation describes the phenomenon where a specific cognitive process is assumed by a homologous region in the contralateral hemisphere. For example, this adaptation mechanism enables the relocation of a cognitive task from a compromised brain region to its corresponding homologous area in the opposing hemisphere. This form of functional neuroplasticity is typically observed in pediatric populations more frequently than in adults.
Map expansion
Map expansion refers to the enlargement of cortical maps associated with specific cognitive tasks, a phenomenon driven by repeated exposure to relevant stimuli. Experimental evidence supports map expansion, particularly from studies investigating the impact of frequent stimulation on brain functional connectivity in individuals acquiring spatial navigation skills.
Cross-modal Reassignment
Cross-modal reassignment describes a process where a brain region, having been deprived of its typical input, begins to receive and process novel sensory signals.
Compensatory Masquerade
Functional plasticity, manifested as compensatory masquerade, involves the utilization of alternative cognitive processes to accomplish an established cognitive task when the primary process is compromised by impairment.
Functional neuroplasticity in the brain can manifest in response to two distinct categories of events:
- Prior neural activity, termed activity-dependent plasticity, which facilitates memory acquisition, or
- Neuronal malfunction or damage, referred to as maladaptive plasticity, which serves to compensate for a pathological event.
In the latter scenario, brain functions may relocate from one region to another, driven by the imperative to restore behavioral or physiological processes. Among the physiological manifestations of activity-dependent plasticity, those involving synapses are categorized as synaptic plasticity. The processes of synaptic strengthening and weakening, which lead to an increase or decrease in neuronal firing rates, are known as long-term potentiation (LTP) and long-term depression (LTD), respectively. Both LTP and LTD are considered fundamental examples of synaptic plasticity intrinsically linked to memory formation. The cerebellum exemplifies a brain structure characterized by a combination of LTP and LTD mechanisms, alongside inherent circuit redundancy, which facilitates plasticity across multiple sites. Recent research increasingly indicates that synaptic plasticity is augmented by another form of activity-dependent plasticity: intrinsic plasticity, which involves alterations in the intrinsic excitability of neurons. Unlike homeostatic plasticity, intrinsic plasticity does not primarily aim to maintain overall neuronal activity within a network but rather plays a crucial role in memory encoding. Furthermore, numerous investigations have demonstrated functional neuroplasticity at the level of brain networks, where targeted training can modify the strength of functional connections. However, a recent study posits that these observed network alterations may not directly constitute neuroplasticity, suggesting they might instead reflect the brain network's inherent requirement for systematic reorganization.
Applications and Illustrative Examples
The adult brain is not characterized by entirely immutable, "hard-wired" neuronal circuits. Instead, numerous instances of cortical and subcortical neuronal circuit reorganization have been documented, occurring both in response to specific training regimens and following injury.
Substantial evidence supports the active, experience-dependent reorganization of the brain's synaptic networks, encompassing multiple interconnected structures, including the cerebral cortex. The precise molecular and ultrastructural mechanisms underlying this process remain subjects of intensive neuroscience research. The profound influence of experience on the brain's synaptic organization forms the foundational premise for several theories of brain function, such as the general theory of mind and neural Darwinism. Furthermore, the concept of neuroplasticity is fundamental to theories of memory and learning, particularly those involving experience-driven modifications to synaptic structure and function, as observed in classical conditioning studies using invertebrate models like Aplysia.
Evidence indicates that neurogenesis, the generation of new brain cells, occurs in the adult rodent brain, with these changes potentially enduring into advanced age. While neurogenesis is primarily documented in the hippocampus and olfactory bulb, research suggests that other brain regions, including the cerebellum, may also exhibit this phenomenon. Nevertheless, the precise extent of circuit rewiring facilitated by the integration of these new neurons into existing networks remains undetermined, and such rewiring could potentially be functionally redundant.
Addiction
Treatment of Brain Damage
A notable implication of neuroplasticity is that brain activity associated with a specific function may relocate to alternative cortical regions. This phenomenon arises from typical experiences and is also observed during recovery from cerebral trauma. Fundamentally, neuroplasticity underpins the scientific rationale for treating acquired brain injuries through goal-directed experiential therapeutic interventions within rehabilitative frameworks, addressing the functional sequelae of such injuries.
Neuroplasticity is increasingly recognized as a theoretical framework that partially accounts for enhanced functional recovery observed in post-stroke physical therapy. Evidence-backed rehabilitation modalities that propose cortical reorganization as their underlying mechanism comprise constraint-induced movement therapy, functional electrical stimulation, treadmill training with body-weight support, and virtual reality therapy. Robot-assisted therapy represents an emergent technique, similarly hypothesized to operate via neuroplasticity; however, definitive evidence regarding its precise mechanisms of action remains limited.
A specific research team has devised a therapeutic approach involving elevated progesterone administration in individuals with brain injuries. "Administration of progesterone after traumatic brain injury (TBI) and stroke reduces edema, inflammation, and neuronal cell death, and enhances spatial reference memory and sensory-motor recovery." Preliminary clinical trials indicated a 60% reduction in mortality among severely injured patients following three days of progesterone injections. Conversely, a 2014 study published in the New England Journal of Medicine, which presented findings from an NIH-funded, multi-center phase III clinical trial involving 882 patients, concluded that progesterone treatment for acute traumatic brain injury offered no statistically significant advantage over placebo.
Binocular Vision
Historically, it was posited that the acquisition of binocular vision, specifically stereopsis, was restricted to early childhood development, with permanent deficits resulting from failure to achieve it during this critical period. Nevertheless, recent advancements demonstrating successful improvements in individuals with amblyopia, convergence insufficiency, or other stereoscopic vision anomalies serve as compelling illustrations of neuroplasticity. Consequently, the enhancement of binocular vision and the restoration of stereopsis constitute active domains of scientific and clinical inquiry.
Phantom Limbs
Phantom limb sensation describes the persistent perception of pain or other tactile experiences originating from a body part that has been surgically removed. This phenomenon is remarkably prevalent, affecting 60–80% of amputees. A neuroplasticity-based explanation posits that the cortical representations of the absent limbs become functionally integrated with adjacent somatosensory areas within the postcentral gyrus. Consequently, neural activity from these surrounding cortical regions is erroneously interpreted by the cortical area previously dedicated to the amputated limb.
The interplay between phantom limb sensation and neuroplasticity is intricate. During the early 1990s, V.S. Ramachandran proposed that phantom limbs arose from cortical remapping. Conversely, in 1995, Herta Flor and her collaborators demonstrated that cortical remapping is exclusively observed in patients experiencing phantom pain. Their investigation indicated that phantom limb pain, as distinct from referred sensations, served as the perceptual manifestation of cortical reorganization. This specific phenomenon is occasionally termed maladaptive plasticity.
In 2009, Lorimer Moseley and Peter Brugger conducted an experiment where arm amputee participants were instructed to employ visual imagery to manipulate their phantom limbs into anatomically impossible configurations. Remarkably, four out of the seven participants successfully executed these impossible phantom limb movements. This study implies that the participants had altered the neural representation of their phantom limbs and subsequently generated the requisite motor commands for impossible movements, even without somatosensory feedback.
Chronic Pain
Chronic pain manifests as persistent discomfort in areas that may have sustained prior injury but are otherwise currently healthy. This phenomenon is attributed to maladaptive neuroplastic reorganization within both peripheral and central nervous systems. Tissue damage, noxious stimuli, and inflammation elevate nociceptive input from the periphery to the central nervous system. Persistent peripheral nociception subsequently triggers a cortical neuroplastic response, altering the somatotopic organization of the painful region and inducing central sensitization. For example, patients with complex regional pain syndrome exhibit a reduced contralateral cortical somatotopic representation of the hand and diminished spatial separation between the hand and mouth representations. Furthermore, chronic pain is associated with a significant global reduction in brain grey matter volume, particularly in the prefrontal cortex and right thalamus. Nevertheless, treatment can resolve these abnormalities in cortical reorganization and grey matter volume, alongside symptom alleviation. Comparable findings have been documented for phantom limb pain, chronic low back pain, and carpal tunnel syndrome.
Meditation
Research indicates a correlation between meditation practice and variations in cortical thickness or grey matter density. A prominent study illustrating this phenomenon was conducted by Sara Lazar of Harvard University in 2000. Richard Davidson, a neuroscientist at the University of Wisconsin, has conducted collaborative experiments with the Dalai Lama investigating meditation's effects on the brain. His findings propose that meditation can induce structural changes in brain regions linked to attention, anxiety, depression, fear, anger, and compassion, in addition to influencing the body's self-healing capacity.
Artistic engagement and art therapy
Substantial evidence suggests that artistic engagement within a therapeutic context can foster alterations in neural network connections and enhance cognitive flexibility. A 2013 study revealed that sustained, habitual artistic training (e.g., musical instrument practice, intentional painting) can "macroscopically imprint a neural network system of spontaneous activity, wherein associated brain regions become functionally and topologically modularized in both domain-general and domain-specific ways." This implies that brains consistently exposed to artistic training over extended durations develop adaptations that facilitate and increase the spontaneous occurrence of such activities.
Certain researchers and academics propose that artistic engagement has significantly influenced the human brain throughout evolutionary history. D.W. Zaidel, an adjunct professor of behavioral neuroscience and a contributor at VAGA, posits that "evolutionary theory connects the symbolic essence of art to crucial pivotal brain transformations in Homo sapiens, thereby supporting enhanced language development and hierarchical social organization."
Music therapy
Evidence indicates that participation in music-supported therapy can enhance neuroplasticity in patients recovering from brain injuries. This therapy is applicable for stroke rehabilitation; a one-month study demonstrated significant improvements in motor control of the affected hand among stroke patients undergoing music-supported therapy. Further research examining grey matter volume in adults experiencing brain atrophy and cognitive decline suggests that playing a musical instrument, such as the piano, or listening to music can augment grey matter volume in regions including the caudate nucleus, Rolandic operculum, and cerebellum. Additionally, music-supported therapy appears to enhance cognitive performance, well-being, and social behavior in patients recovering from orbitofrontal cortex (OFC) damage and mild traumatic brain injury. Post-therapy neuroimaging revealed functional alterations within OFC networks, with improvements evident in both task-based and resting-state fMRI analyses.
In addition to its role in clinical rehabilitation, musical engagement has been demonstrated to elicit neuroplastic alterations in healthy individuals via sustained training and repeated exposure. Comparative research involving musicians and non-musicians reveals distinct structural and functional cerebral variations linked to musical engagement, especially when musical instruction commences during early developmental stages. Individuals with musical training frequently display augmented gray and white matter volumes within motor, auditory, and cerebellar cortical areas, indicative of adaptations pertaining to refined motor control, auditory information processing, and temporal coordination. Furthermore, evidence of cortical reorganization has been documented, manifesting as expanded cortical representations for digits predominantly utilized during instrumental performance.
Musical instruction profoundly influences the auditory system, as evidenced by musicians exhibiting heightened activation and structural distinctions within the primary and secondary auditory cortices, which are crucial for processing pitch, rhythm, and melody. Functional modifications extend beyond the cortical level, encompassing subcortical structures as well, such as the brainstem, where musicians demonstrate more rapid and robust neural responses to auditory stimuli. Throughout an individual's lifespan, consistent musical involvement has been correlated with a diminished age-associated decline in specific cerebral areas and a reduced susceptibility to cognitive impairment, implying that neuroplasticity induced by music could foster enduring brain health.
Physical Fitness and Exercise
Aerobic physical activity stimulates the synthesis of neurotrophic factors (biomolecules that facilitate neuronal growth and survival), including brain-derived neurotrophic factor (BDNF), insulin-like growth factor 1 (IGF-1), and vascular endothelial growth factor (VEGF). The effects of exercise on the hippocampus are linked to quantifiable enhancements in spatial memory. Sustained aerobic exercise, maintained over several months, elicits substantial and clinically significant improvements in executive function (defined as the cognitive regulation of behavior) and an augmentation of gray matter volume across numerous brain regions, especially those integral to cognitive control. The cerebral structures exhibiting the most pronounced increases in gray matter volume following aerobic exercise are the prefrontal cortex and the hippocampus, while moderate enhancements are observed in the anterior cingulate cortex, parietal cortex, cerebellum, caudate nucleus, and nucleus accumbens. Superior physical fitness levels (quantified by VO2 max) correlate with enhanced executive function, accelerated processing speed, and larger volumes of the hippocampus, caudate nucleus, and nucleus accumbens.
Auditory Deprivation and Hearing Loss
In individuals experiencing hearing loss, the auditory cortex and associated cerebral regions in deaf and hard-of-hearing populations exhibit compensatory neuroplasticity. This auditory cortex, typically dedicated to processing auditory stimuli in individuals with normal hearing, is subsequently repurposed to facilitate other sensory modalities, particularly vision and somatosensation.
Deaf individuals demonstrate heightened peripheral visual attention, superior detection of motion changes but not color changes in visual tasks, more efficient visual search strategies, and quicker response times to visual targets when contrasted with hearing individuals. Modifications in visual processing among deaf individuals are frequently linked to the functional reallocation of other cerebral regions, such as the primary auditory cortex, the posterior parietal association cortex (PPAC), and the anterior cingulate cortex (ACC). A comprehensive review by Bavelier et al. (2006) provides an extensive overview of various facets concerning the comparison of visual abilities between deaf and hearing individuals.
In individuals with congenital deafness, cerebral regions typically involved in auditory processing are repurposed to process somatosensory information. These individuals exhibit increased sensitivity in detecting suprathreshold frequency changes in vibration and demonstrate more pronounced and spatially extensive activation within the auditory cortex during somatosensory stimulation. Nevertheless, an accelerated response to somatosensory stimuli has not been observed in deaf adults.
Cochlear Implants
Neuroplasticity plays a crucial role in the development of sensory function. The brain, immature at birth, subsequently adapts to sensory inputs. Within the auditory system, congenital hearing loss, a relatively common congenital condition impacting approximately 1 in 1000 neonates, has been demonstrated to impair auditory development. However, the implantation of sensory prostheses that activate the auditory system has mitigated these deficits and fostered functional maturation of the auditory system. Given the existence of a sensitive period for neuroplasticity, a corresponding critical window for such intervention exists during the initial 2 to 4 years of life. Consequently, in prelingually deaf children, early cochlear implantation typically enables them to acquire their native language and develop acoustic communication skills.
Blindness
In individuals experiencing vision loss, the visual cortex may exhibit cross-modal plasticity, potentially leading to enhanced capabilities in other sensory modalities. Conversely, the absence of visual input might impede the development of other sensory systems. A specific study suggests that the right posterior middle temporal gyrus and superior occipital gyrus exhibit greater activation in blind individuals than in sighted persons during a sound-movement detection task. Multiple investigations corroborate this latter hypothesis, reporting diminished performance in audio distance evaluation, proprioceptive reproduction, visual bisection thresholds, and the assessment of minimum audible angles.
Human echolocation
Human echolocation represents a learned human capacity to perceive the environment through echoes. Certain blind individuals employ this skill for detailed environmental navigation and perception. Research conducted in 2010 and 2011, utilizing functional magnetic resonance imaging (fMRI) techniques, has demonstrated that brain regions typically associated with visual processing adapt to facilitate the novel skill of echolocation. For instance, investigations involving blind patients indicate that the click-echoes they perceive are processed by cerebral areas dedicated to vision, rather than those typically involved in audition.
Attention deficit hyperactivity disorder
Analyses of magnetic resonance imaging (MRI) and electroencephalography (EEG) studies concerning individuals with Attention Deficit Hyperactivity Disorder (ADHD) indicate that prolonged stimulant therapy for ADHD, including agents like amphetamine or methylphenidate, mitigates structural and functional brain abnormalities observed in ADHD subjects. Furthermore, it enhances functionality in various cerebral regions, specifically mentioning the right caudate nucleus of the basal ganglia, the left ventrolateral prefrontal cortex (VLPFC), and the superior temporal gyrus.
Beyond pharmacological interventions, non-pharmacological strategies harnessing neuroplasticity have been posited as viable methods for addressing ADHD symptomatology. Cognitive training and various behavioral therapies endeavor to enhance attention, self-regulation, and impulse control by fostering functional and structural alterations within neural circuits linked to executive function. Computerized cognitive training programs have demonstrated efficacy in targeting underdeveloped neural networks in individuals with ADHD, resulting in enhancements in attention and working memory via repetitive stimulation of distinct brain regions. Such interventions may induce enduring neuroplastic modifications that correspond with cerebral areas influenced by stimulant medications, thereby implying that neuroplasticity-driven therapies could serve as complementary treatments or, in certain instances, diminish the necessity for pharmacological reliance.
In early child development
Neuroplasticity exhibits its highest activity during childhood, constituting a fundamental aspect of typical human development, and is recognized as a particularly vital mechanism for children concerning both risk and resilience. Trauma poses a significant risk, as it detrimentally impacts numerous brain regions and imposes chronic stress on the sympathetic nervous system due to persistent activation. Consequently, trauma modifies neural connections, potentially leading to hypervigilance or excessive arousal in children who have undergone such experiences. Nevertheless, a child's brain possesses the capacity to mitigate these adverse effects through neuroplastic processes.
Neuroplasticity manifests in children across four distinct categories, encompassing a broad spectrum of neuronal functioning. These four classifications are identified as impaired, excessive, adaptive, and plasticity.
Numerous instances of neuroplasticity are evident in human development. For example, Justine Ker and Stephen Nelson investigated the impact of musical training on neuroplasticity, demonstrating that such training fosters experience-dependent structural plasticity. This phenomenon involves neural modifications contingent upon an individual's unique experiences. Such experiences include multilingual acquisition, athletic engagement, and theatrical participation. Research conducted by Hyde in 2009 revealed observable cerebral alterations in children after merely 15 months of musical instruction. Ker and Nelson propose that this level of neural plasticity in pediatric brains could offer a therapeutic intervention for children afflicted with developmental disorders and neurological conditions.
Neuroplasticity in Animal Organisms
Throughout an individual's lifespan, animal species can exhibit diverse alterations in brain morphology. A significant proportion of these variations stems from the release of hormones within the brain, while others arise from evolutionary factors or developmental stages. Certain modifications manifest seasonally within species, serving to augment or elicit specific behavioral responses.
Seasonal Cerebral Modifications
The adaptation of cerebral behavior and morphology to align with other seasonal activities is a prevalent phenomenon in animal species. Such alterations can enhance reproductive success during the breeding period. Illustrations of seasonal cerebral morphological shifts are evident across numerous taxonomic classes and species.
Within the avian class, specifically in black-capped chickadees, an augmentation in hippocampal volume and the robustness of its neural connections is observed during autumnal periods. These hippocampal morphological transformations, pertinent to spatial memory, are not exclusive to avian species, being similarly detectable in rodents and amphibians. For instance, numerous song control nuclei within the brains of songbirds exhibit hypertrophy during the reproductive season. Across avian species, cerebral morphological adaptations that modulate song patterns, frequency, and amplitude are frequently documented. Furthermore, gonadotropin-releasing hormone (GnRH) immunoreactivity, indicative of hormone reception, diminishes in European starlings subjected to extended photoperiods.
The gastropod Aplysia californica (California sea hare) demonstrates enhanced inhibition of egg-laying hormones outside the mating season, attributed to augmented efficacy of cerebral inhibitors. Similar alterations in the inhibitory characteristics of specific brain regions are also observed in humans and other mammalian species. In the amphibian Bufo japonicus, a segment of the amygdala exhibits greater dimensions prior to breeding and throughout hibernation compared to its post-breeding state.
Seasonal cerebral variability is evident across numerous mammalian species. A specific hypothalamic region in the common ewe exhibits heightened receptivity to GnRH during the breeding season compared to other annual periods. Humans also undergo seasonal modifications, with the hypothalamic suprachiasmatic nucleus and its vasopressin-immunoreactive neurons increasing in size during autumn, subsequently diminishing in dimensions during spring.
Investigations into Traumatic Brain Injury
Researchers have observed that inducing a minor stroke (infarction) via obstructed blood flow to a segment of a monkey's motor cortex results in movement responses from the corresponding body part when adjacent, undamaged cerebral regions are stimulated. One investigation employed intracortical microstimulation (ICMS) mapping techniques on nine healthy monkeys; a subset of these animals underwent ischemic-infarction procedures, while the remainder received ICMS procedures. Monkeys subjected to ischemic infarctions exhibited greater finger flexion during food retrieval, and this functional deficit resolved to preoperative levels within several months. Regarding distal forelimb representation, "postinfarction mapping procedures revealed that movement representations underwent reorganization throughout the adjacent, undamaged cortex." Comprehending the interplay between compromised and intact neural regions offers a foundation for developing superior therapeutic strategies for stroke patients. Contemporary research endeavors involve monitoring the alterations that manifest in the motor cortices following a cerebrovascular accident. Consequently, the dynamics of cerebral reorganization can be elucidated. Furthermore, therapeutic regimens designed to augment stroke recovery, including physiotherapy, pharmacotherapy, and electrical stimulation therapy, are currently under investigation.
Professor Jon Kaas of Vanderbilt University has demonstrated the impact of chronic unilateral dorsal-column lesions at cervical levels on somatosensory area 3b and the ventroposterior (VP) nucleus of the thalamus in macaque monkeys. While adult brains possess the capacity for post-injury reorganization, the degree of this change is contingent upon the injury's severity. Kaas's recent investigations primarily explore the somatosensory system, which integrates various sensory inputs to perceive the body and its movements. Typically, damage to the somatosensory cortex leads to impaired body perception. His research specifically examines how somatosensory, cognitive, and motor systems exhibit plastic alterations following injury.
A recent neuroplasticity study, conducted by a team of physicians and researchers at Emory University, including Donald Stein and David Wright, explored a novel treatment for traumatic brain injuries. This intervention, reportedly the first in four decades to yield significant results, was noted for its absence of known side effects and cost-effectiveness. Stein observed that female mice exhibited superior recovery from brain injuries compared to male mice, with recovery further enhanced during specific phases of the estrus cycle. This disparity was hypothesized to stem from varying progesterone levels, where elevated progesterone correlated with accelerated brain injury recovery in mice. Nevertheless, subsequent clinical trials indicated that progesterone provided no substantial benefit for human patients with traumatic brain injury.
Aging
Transcriptional profiling of the frontal cortex in individuals aged 26 to 106 years identified a cohort of genes exhibiting diminished expression post-age 40, with a more pronounced reduction after age 70. Genes critical for synaptic plasticity were particularly susceptible to age-related changes, typically demonstrating decreased expression over time. Furthermore, aging was associated with a notable increase in cortical DNA damage, likely oxidative in nature, specifically within gene promoters.
Reactive oxygen species (ROS) are implicated in the regulation of synaptic plasticity and cognitive function. Conversely, age-associated elevations in ROS levels may contribute to the deterioration of these same functions.
Multilingualism
Multilingualism confers advantageous effects on human behavior and cognition. Extensive research indicates that individuals proficient in multiple languages exhibit superior cognitive functions and greater cognitive flexibility compared to monolinguals. Bilinguals have been observed to possess extended attention spans, enhanced organizational and analytical abilities, and a more developed theory of mind than their monolingual counterparts. Investigators attribute the cognitive benefits of multilingualism to neuroplasticity.
A notable study employed voxel-based morphometry (VBM) to visualize structural brain plasticity in healthy monolingual and bilingual individuals. Neurolinguists initially examined variations in grey and white matter density between these groups and identified a correlation between brain structure and the age of language acquisition. The findings revealed that multilinguals exhibited significantly higher grey-matter density in the inferior parietal cortex compared to monolinguals. Furthermore, early bilinguals demonstrated greater grey matter density in this region than late bilinguals. The inferior parietal cortex, a brain area strongly implicated in language acquisition, aligns with the VBM outcomes of this investigation.
Contemporary research indicates that acquiring multiple languages not only induces structural reorganization within the brain but also enhances its inherent capacity for plasticity. A recent investigation specifically revealed that multilingualism impacts both grey and white matter. White matter, composed of myelinated axons, is fundamentally linked to learning and communication processes. Neurolinguists utilized diffusion tensor imaging (DTI) to assess white matter intensity differences between monolinguals and bilinguals. The study identified increased myelination in white matter tracts among bilingual individuals who regularly engaged with both languages. The cognitive demands associated with managing multiple languages necessitate more efficient neural connectivity, thereby contributing to greater white matter density in multilinguals.
Although the etiology of these cerebral alterations—whether genetic predisposition or environmental demands—remains a subject of debate, substantial evidence indicates that environmental and social experiences in early multilingual individuals influence the structural and functional reorganization of the brain.
Emerging Therapeutic Approaches for Depression
Historically, the monoamine imbalance hypothesis of depression significantly influenced psychiatric understanding and pharmaceutical development. Nevertheless, despite traditional antidepressants rapidly elevating noradrenaline, serotonin, or dopamine levels, their clinical efficacy often manifests with a considerable delay, frequently resulting in suboptimal treatment outcomes. As neuroscientific inquiry progressed, clinical and preclinical data from diverse research modalities began to highlight pathways integral to neuroplasticity. Researchers identified a robust inverse correlation between synaptic density and the severity of depressive symptoms. Furthermore, it was observed that traditional antidepressants, beyond their neurotransmitter modulation, also enhanced neuroplasticity, albeit over an extended period spanning weeks or months. The quest for more rapidly acting antidepressants led to the investigation of ketamine, a recognized anesthetic agent, which demonstrated potent antidepressant effects following a single infusion. This efficacy is attributed to its ability to swiftly augment dendritic spine density and reinstate aspects of functional connectivity. Subsequently, other neuroplasticity-promoting compounds exhibiting both rapid and sustained therapeutic benefits have been identified, encompassing serotonergic psychedelics, cholinergic scopolamine, and various other novel agents. To distinguish between conventional antidepressants primarily targeting monoamine modulation and this emerging class of fast-acting antidepressants that achieve therapeutic effects via neuroplasticity, the term "psychoplastogen" has been introduced.
Nicotine's Influence
Nicotine exerts its effects on the brain by interacting with nicotinic acetylcholine receptors, which are also the binding sites for acetylcholine and have been associated with neuroplasticity. Chronic nicotine consumption may diminish the rate of cerebral neuroplasticity by impairing these nicotinic-acetylcholine receptors, which are essential for the reuptake of acetylcholine required for neuroplastic processes.
References
References
- Videos
- Ramachandran. Phantom Limb Syndrome.Chorost M (2005). Rebuilt: how becoming part computer made me more human. Boston: Houghton Mifflin. ISBN 978-0-618-37829-6.
- Neuroplasticity at the U.S. National Library of Medicine Medical Subject Headings (MeSH)
- NeuroplasticityMD