Computational study of experience-dependent plasticity in adult rat cortical barrel-column

Abstract

We model experience-dependent plasticity in the adult rat S1 cortical representation of the whiskers (the barrel cortex) which has been produced by trimming all whiskers on one side of the snout except two. This manipulation alters the pattern of afferent sensory activity while avoiding any direct nerve damage. Our simplified model circuitry represents multiple cortical layers and inhibitory neurons within each layer of a barrel-column. Utilizing a computational model we show that the evolution of the response bias in the barrel-column towards spared whiskers is consistent with synaptic modifications that follow the rules of the Bienenstock, Cooper and Munro (BCM) theory. The BCM theory postulates that a neuron possesses a dynamic synaptic modification threshold, thetaM, which dictates whether the neuron's activity at any given instant will lead to strengthening or weakening of the synapses impinging on it. However, the major prediction of our model is the explanation of the delay in response potentiation in the layer-IV neurons through a masking effect produced by the thresholded monotonically increasing inhibition expressed by either the logarithmic function, h(x) = mu log(1 + x), or by the power function, h(x) = mu x(0.8-0.9), where mu is a constant. Furthermore, simulated removal of the supragranular layers (layers II/III) reduces plasticity of neurons in the remaining layers (IV-VI) and points to the role of noise in synaptic plasticity.

Retuning of Inferior Colliculus Neurons Following Spiral Ganglion Lesions: A Single-Neuron Model of Converging Inputs

“…Acute changes in RF might also be explained by other forms of synaptic plasticity. Hebbian synaptic plasticity (Hebb 1949) has been proposed as a mechanism for the maintenance of cortical RFs in several modalities (Pearson et al 1987; Armentrout et al 1994; Benuskova et al 1994; Jenison 1997; Benuskova et al 1999) and models of it can reproduce (Jenison 1997) the normal development of tonotopy (Reale et al 1987) and the changes following lesions reported by Robertson and Irvine (1989). Another possibility is that multineuron circuitry could result in processing that is functionally similar to that which we see in dendrites in this model.…”

Neural Computation via Neural Geometry: A Place Code for Inter-whisker Timing in the Barrel Cortex?

“…Given the remarkable spatial relationship between the whisker and its associated barrel column, it is surprising that, with the exception of refs. [65], [66] and our own previous model [44], connection geometry has not been an important factor in computational neuroscience models of the barrel system.…”

Theory for normal and impaired experience-dependent plasticity in neocortex of adult rats

“…The inputs from cut whiskers were assumed to relay noise for 100% of time steps, i.e., d i vpm (t) ϭ n i vpm (t) and d i cor (t) ϭ n i cor (t) for i ϭ D-cut (D3), C2, and E2. The level (or amplitude) of noise plays an important role in synaptic modification according to the Bienenstock, Cooper, Munro (BCM) theory because it determines the magnitude of decrease of synaptic weights when the cell response c is below M and close to zero (7,20). The two spared whiskers, D2 and D1, were ''stimulated'' at random, either both at once or each one alone.…”

“…We have found that circuitry within the adult rat barrel cortex is modified by innocuous changes in whisker experience in accordance with the BCM rules of synaptic plasticity (3)(4)(5)(6)(7). Any model for activity-dependent plasticity in cortex must satisfy the central concept of adequate intracellular calcium entry through depolarization-dependent calcium permeable receptors, which in turn induce a cascade of molecular changes leading to LTP or LTD (2).…”