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I. Evidence for a Predominance of Silent Cortical Neurons in Sensorimotor Cortices................................................................................2 A. Evaluation of Presynaptic Activity

in the Somatosensory Cortex.................................................................3 1. Results from Extracellular Unit Recording ....................................3 2. Results from Sharp Microelectrode Recordings.............................3 3. Results from Whole-Cell Recordings in the Vibrissae

Barrel Cortices of Anesthetized Animals .......................................4 4. Results from Whole-Cell Recordings in the Vibrissae

Barrel Cortices of Awake Animals .................................................4 5. Inconsistencies and Caveats from Whole-Cell Studies ..................6 6. Results from Derivatives of the Whole-Cell

Recordings Technique .....................................................................6 7. All Techniques Agree that Firing Rates of Cortical Neurons

are Very Heterogeneous ..................................................................7 B. Evaluation of Postsynaptic Activty

in the Somatosensory Cortex.................................................................7 1. Experimental Agreement on the Amplitude

of Subthreshold Signals ...................................................................7 2. The Synaptic Composition of Postsynaptic Responses

Is Controversial................................................................................8 3. An Attempt to Quantitatively Determine the Synaptic

Composition of a Cortical Sensory Response Suggests Very Low Presynaptic Activity .......................................................8