Figure 5. Diagram of interareal connections subserving interactions between areas 3a and 3b/1.

The regions in areas 3a and 3b/1 that process input from the same body region are linked by glutamatergic (excitatory) connections arising from pyramidal neurons of each area. These axonal connections terminate synaptically on both excitatory and inhibitory interneurons. Due to greater responsivity of inhibitory interneurons relative to excitatory interneurons, the overall effect of the interareal connections on the target neuronal population typically is inhibitory, as in the competitive interactions that occur frequently between areas 3a and 3b/1. However, in vigorously activated SI cell columns, the normally inhibitory synaptic action of GABA has been postulated to diminish due to activity-dependence of neuronal [Cl⁻]_I [133]. When this occurs, GABA's action switches to excitation, and the normally inhibitory interaction between areas becomes facilitatory. Such a transformation of the cortical action of GABA would be accompanied by an alteration of perception. For example, a tactile stimulus could be experienced as painful if vigorous activation of 3b/1 triggers activity in area 3a nociresponsive neurons proposed to underlie slow/2^nd/burning pain. Such a modification of the action of GABA would be accompanied by allodynia – a common clinical malady.