Abstract
Despite the fact that there is a growing awareness to the callosal connections between hemispheres the two hemispheres of the brain are commonly treated as independent structures when peripheral or cortical manipulations are applied to one of them. The contralateral hemisphere is often used as a within-animal control of plastic changes induced onto the other side of the brain. This ensures uniform conditions for producing experimental and control data, but it may overlook possible interhemispheric interactions. In this paper we provide, for the first time, direct proof that cortical, experience-dependent plasticity is not a unilateral, independent process. We mapped metabolic brain activity in rats with 2-[14C] deoxyglucose (2DG) following experience-dependent plasticity induction after a month of unilateral (left), partial whiskers deprivation (only row B was left). This resulted in ∼45% widening of the cortical sensory representation of the spared whiskers in the right, contralateral barrel field (BF). We show that the width of 2DG visualized representation is less than 20% when only contralateral stimulation of the spared row of whiskers is applied in immobilized animals. This means that cortical map remodeling, which is induced by experience-dependent plasticity mechanisms, depends partially on the contralateral hemisphere. The response, which is observed by 2DG brain mapping in the partially deprived BF after standard synchronous bilateral whiskers stimulation, is therefore the outcome of at least two separately activated plasticity mechanisms. A focus on the integrated nature of cortical plasticity, which is the outcome of the emergent interactions between deprived and non-deprived areas in both hemispheres may have important implications for learning and rehabilitation. There is also a clear implication that there is nothing like “control hemisphere” since any plastic changes in one hemisphere have to have influence on functioning of the opposite one.
Highlights
Rodents whiskers’ representation in the somatosensory cortex is widely used as a model of cortical plasticity due to its highly somatotopic organization
Uni- and bilateral whiskers stimulations lead to a different pattern of experience-dependent plasticity effects. In these two cases the visualization of the experience dependent plasticity by 2-[14C] deoxyglucose (2DG) incorporation differed significantly (p ≤ 0.05). Both types of stimulation generated a band of the representation of sensory row B in the barrel field (BF) that is contralateral to the stimulated rows and more laterally in the neighboring SII (Figures 1Ac,d)
Our results show that the cortical areas engaged in experiencedependent plasticity cortical map remodeling are differently activated during uni- and bilateral stimulation, suggesting contralateral hemisphere participation in cortical plasticity
Summary
Rodents whiskers’ representation in the somatosensory cortex is widely used as a model of cortical plasticity due to its highly somatotopic organization. It was shown (in rats) that a month of unilateral, partial whiskers deprivation results in the widening of the spared whiskers representation at the expense of surrounding area of the deprived whiskers representations (Kossut et al, 1988; Diamond et al, 1993; Fox, 1994). Bilateral whiskers’ stimulation was often used to visualize the cortical plasticity changes in one hemisphere and was compared to the opposite hemisphere, which was treated as a control (Jablonka et al, 2007, 2012; Kaliszewska et al, 2012) In this experimental model, the unilateral partial whiskers deprivation induces plastic changes in the contralateral hemisphere, increasing it by almost 50% when visualized by 2DG incorporation. We wanted to see if the response to an acute unilateral whiskers stimulation after chronic experiencedependent plasticity induction results in the same pattern of plastic rearrangement of the spared whiskers cortical representations as that resulting from bilateral stimulation
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