It has been clear for almost two decades that cortical representations in adult animals are not fixed entities, but rather, are dynamic and are continuously modified by experience. The cortex can preferentially allocate area to represent the particular peripheral input sources that are proportionally most used. Alterations in cortical representations appear to underlie learning tasks dependent on the use of the behaviorally important peripheral inputs that they represent. The rules governing this cortical representational plasticity following manipulations of inputs, including learning, are increasingly well understood. In parallel with developments in the field of cortical map plasticity, studies of synaptic plasticity have characterized specific elementary forms of plasticity, including associative long-term potentiation and long-term depression of excitatory postsynaptic potentials. Investigators have made many important strides toward understanding the molecular underpinnings of these fundamental plasticity processes and toward defining the learning rules that govern their induction. The fields of cortical synaptic plasticity and cortical map plasticity have been implicitly linked by the hypothesis that synaptic plasticity underlies cortical map reorganization. Recent experimental and theoretical work has provided increasingly stronger support for this hypothesis. The goal of the current paper is to review the fields of both synaptic and cortical map plasticity with an emphasis on the work that attempts to unite both fields. A second objective is to highlight the gaps in our understanding of synaptic and cellular mechanisms underlying cortical representational plasticity.

/pdf/cortical-plasticity-from-synapses-to-maps-2j9eoi9428.pdf

CORTICAL PLASTICITY: From Synapses to Maps

Timing based LTP and LTD at vertical inputs to layer II/III pyramidal cells in rat barrel cortex

https://www.math.fsu.edu/~dgalvis/journalclub/papers/04_13_2015.pdf

Cortical Development and Remapping through Spike Timing-Dependent Plasticity

The Role of Spike Timing in the Coding of Stimulus Location in Rat Somatosensory Cortex

Recent findings in neuroscience suggest that adult brain structure changes in response to environmental alterations and skill learning. Whereas much is known about structural changes after intensive practice for several months, little is known about the effects of single practice sessions on macroscopic brain structure and about progressive (dynamic) morphological alterations relative to improved task proficiency during learning for several weeks. Using T1-weighted and diffusion tensor imaging in humans, we demonstrate significant gray matter volume increases in frontal and parietal brain areas following only two sessions of practice in a complex whole-body balancing task. Gray matter volume increase in the prefrontal cortex correlated positively with subject's performance improvements during a 6 week learning period. Furthermore, we found that microstructural changes of fractional anisotropy in corresponding white matter regions followed the same temporal dynamic in relation to task performance. The results make clear how marginal alterations in our ever changing environment affect adult brain structure and elucidate the interrelated reorganization in cortical areas and associated fiber connections in correlation with improvements in task performance.

https://www.jneurosci.org/content/jneuro/30/35/11670.full.pdf

Dynamic Properties of Human Brain Structure: Learning-Related Changes in Cortical Areas and Associated Fiber Connections

The effect of innocuously biasing the flow of sensory activity from the whiskers for periods of 3-30 d in awake, behaving adult rats on the receptive field organization of rat SI barrel cortex neurons was studied One pair of adjacent whiskers, D2 and either D1 or D3, remained intact unilaterally (whisker pairing), all others being trimmed throughout the period of altered sensation Receptive fields of single cells in the contralateral D2 barrel were analyzed under urethane anesthesia by peristimulus time histogram (PSTH) and latency histogram analysis after 3, 7-10, and 30 d of pairing and compared with controls, testing all whiskers cut to the same length Response magnitudes to surround receptive field in-row whiskers D1 and D3 were not significantly different for control animals The same was found for surround in-arc whiskers C2 and E2 However, after 3 d of whisker pairing a profound bias occurred in response to the paired D-row surround whisker relative to the opposite trimmed surround D-row whisker and to the C2 and E2 whiskers This bias increased with the duration of pairing, regardless of which surround whisker (D1 or D3) was paired with D2 For all three periods of pairing the mean response to the paired surround whisker was increased relative to controls, but peaked at 7-10 d Response to the principal center-receptive (D2) whisker was increased for the 3 and 7-10 d groups and then decreased at 30 d Responses to trimmed arc surround whiskers (C2 and E2) were decreased in proportion to the duration of changed experience Analysis of PSTH data showed that earliest discharges (5-10 msec poststimulus) to the D2 whisker increased progressively in magnitude with duration of pairing For the paired surround whisker similar early discharges newly appeared after 30 d of pairing At 3 and 7-10 d of pairing, increases in response to paired whiskers and decreases to cut surround whiskers were confined to late portions of the PSTH (10-100 msec poststimulus) Changes at 3-10 d can be attributed to alterations in intracortical synaptic relay between barrels Longer-term changes in response to both paired whisker inputs (30 d) largely appear to reflect increases in thalamocortical synaptic efficacy Our findings suggest that novel innocuous somatosensory experiences produce changes in the receptive field configuration of cortical cells that are consistent with Hebbian theories of experience-dependent potentiation and weakening of synaptic efficacy within SI neocortical circuitry, for correlated and uncorrelated sensory inputs, respectively

https://www.jneurosci.org/content/jneuro/14/11/6978.full.pdf

FF Ebner

Papers

An innocuous bias in whisker use in adult rats modifies receptive fields of barrel cortex neurons.