Figure 3.

Typical responses of cortical neurons to thalamic (CL) electrical stimuli. A, Responses of a cortical neuron (area 5) to electrical stimuli delivered to the thalamic LP nucleus. During spontaneous depolarized membrane potentials of the “up-state” of the slow oscillation (upper trace) under low isoflurane anesthesia, we observed the following response sequence: an initial EPSP, a fast IPSP (a), a long lasting hyperpolarization (b), and a sustained rebound depolarization (c). The same stimulus was applied during the hyperpolarized “down-state” (middle trace) and we recorded a very similar response with the exception of a modified short IPSP (a). After BS induction with 3% IF, the initial excitatory response diminished in amplitude despite a further hyperpolarized membrane potential. Moreover, the rebound component (c) appeared mostly abolished (lower trace). B, Absence of inhibitory components in the response of another cortical neuron to thalamic stimulation even under steady depolarization through current injection (+1 nA) to bring the membrane potential at −60 mV. Average of 20 responses. C, Assessment of input resistance: responses under low isoflurane in black, BS responses in red recorded 9 min later (average traces from the same neuron, n = 25). Note the overall increase in resistance during BS (C2). Resistance tests during the time frame of the inhibitory responses after stimulation displayed a lack of resistance modification under BS and an 18% reduced resistance during the low isoflurane condition (C1).