Figure 2.

Neocortical heterotopias are integrated within the neocortical circuitry. (A) Electrical stimulation of the WM evoked an EPSC in both heterotopic and supragranular neurons, but not in CA1 neurons. Holding potential (V_H) = −65 mV. (B) In the presence of 6-cyano-7-dinitroquinoxaline-2,3-dione and 2-amino-5-phosphopentanoate, electrical stimulation of the WM evoked an all-or-none action potential. This was not associated with an EPSP when stimulus intensity was reduced below the threshold for action potential generation. (C) An orthodromic action potential evoked by a depolarizing pulse collided with the stimulus-evoked action potential when the interspike delay (measured as the delay between the two action potential) was below 7 ms. Membrane potential (V_M) = −70 mV. (D) In control conditions, electrical stimulation of the heterotopia evoked a multiphasic EPSP with superimposed action potentials. This multiphasic EPSP was considered as a network-driven event because it was evoked in an all-or-none manner and its latency decreased with increasing stimulus intensity. V_M = −75 mV. (E) In other cells, stimulation of the heterotopia failed to induce any synaptic response in control conditions (upper trace). However, in presence of bicuculline (10 μM), an all-or-none epileptiform discharge was evoked (lower trace). V_M = −78 mV.