Figure 2. Potential functional implication of differential adaptation of intracortical and feedforward synapses in the superficial layers of deprived and spared cortices.

(A)In the deprived cortex, loss of vision triggers global homeostatic scaling up of intracortical excitatory synapses in L2/3 without changes in feedforward synapses from L4. This allows previously weak synapses carrying multisensory information from other senses to cross the threshold and activate L2/3 neurons. Such synaptic plasticity mechanisms may be a cellular basis for cross-modal recruitment of V1 by braille reading. Intracortical excitatory postsynaptic potentials (EPSPs) are depicted in blue and visually evoked EPSP is shown in magenta. Dotted lines represent resting potential and action potential threshold.

(B) In the spared cortices, such as in S1 and A1, vision loss leads to experience-dependent strengthening of feedforward synapses from L4 to L2/3. In addition, there is concomitant global homeostatic scaling down of intracortical excitatory synapses. Such synaptic modification would allow the spared cortex to preferentially process feedforward sensory inputs at the expense of intracortical processing. Intracortical EPSPs are depicted in blue and sensory evoked EPSP is shown in magenta. Dotted lines represent resting potential and action potential threshold.