Objective: The characteristics of the early component of the direct cortical response have not been well studied, although direct cortical response recording is a common method of brain function monitoring.
Methods: In this experimental study, we sought conditions affording the clearest recording of the early potential, by varying the polarity and low-cutoff filter setting, and we confirmed that the early potential consists of two components, P1 and P2.
Results: When subcortical damage was induced by local cerebral compression or saline injection, transient changes in P1 and permanent disappearance of P2 were observed. P2 also disappeared when the fiber connections between the cortex and the basal ganglia, including the thalamus, were destroyed by wire insertion. With deep recording, both P1 and P2 exhibited potential reversal at a level histologically confirmed to be in Layer V of the cortex.
Conclusion: These findings suggest that P1 is a spike reflecting the activity of pyramidal cells evoked by electrical stimulation of the brain surface and that P2 is a potential arising in Layer V of the cortex and is related to afferent fibers from the thalamus. Recording of P2 may be useful for monitoring for subcortical damage.