Figure 1.

Recurrent connectivity in MEC II is provided by interneurons. (a) Quadruple whole-cell recording in vitro from a fast-spiking interneuron (1) and three stellate cells (2, 3 and 4). Only the interneuron responds with excitatory postsynaptic potentials to the stimulation of a stellate cell (middle). By contrast, all stellate cells display inhibitory responses when the interneuron is stimulated (right). (b) Connectivity rates for excitation (black) and recurrent inhibition (red) as a function of postnatal age. Note near-absence of excitatory connections in adult animals. (c) Connectivity rates for inhibitory connections from fast-spiking to stellate cells, excitatory connections from stellate to fast-spiking cells, and the reciprocity of these connections. ((a–c) Adapted with permission from Couey et al. [24].)