Figure 3. Responses of identified barrel cortex CS neurons to whisker stimulation.

A, antidromic identification of CS neurons. Superimposition of 3 successive responses of a barrel cortex layer 5 neuron to electrical stimulations (vertical arrow) of the ipsilateral striatum (top traces). Note the short (0.64 ms), and stable, latency of the first evoked action potential, which was abolished (bottom record) by the collision with a spontaneously occurring orthodromic spike (oblique arrow). This cell displayed an intrinsic bursting pattern (inset) in response to positive current (+0.6 nA) injection (calibrations: 20 mV, 50 ms). B, continuous (1.4 s) intracellular recording (bottom record) from an identified CS neuron and the corresponding surface ECoG activity (top trace). The inset depicts the cross-correlation between both signals, using the cortical surface activity as reference (calibration, 200 ms). Note the high correlation between the two oscillatory signals, at a frequency of ∼7.5 Hz, with a temporal shift of −18.7 ms. C, three successive individual responses in a CS neuron (same as in B) to air-puffs applied on the contralateral whiskers (top). Note the high firing probability (P_F) of the cell in response to sensory stimuli despite the occurrence of a small subthreshold dPSP (asterisk), apparently shunted by a prior synaptic activity. D, barrel cortex ERPs (top records) and corresponding intracellular responses (n = 2) recorded from an identified CS cell (black traces) and an ‘unidentified’ layer 5 cell (grey traces) in the same experiment and in response to the same sensory stimulus (upper trace). As shown by the expanded records (top inset, calibrations: 10 mV, 10 ms), the latency and shape of suprathreshold sensory responses (spikes are truncated) in both cells were very similar. Injection of a positive current pulse (0.6 nA) generated an intrinsic bursting firing pattern in the two neurons (bottom inset, calibrations: 20 mV, 50 ms).