in amplitude were greater for the N50 and P80 components than for the N30. This was
observed to an even greater extent on lead 3, where the amplitude of the N30 did not vary
significantly according to tonal frequency, in spite of the highly significant fluctuations in
P50 and N780 amplitude. On lead 3, the P50 and N80 were less sharply tuned and their
amplitude was maximal at frequencies of 2–3 kHz. Lead 6 recorded neuronal activity in a
region between the lateral part of the primary cortex and the medial part of the secondary
cortex and yielded responses characterized, this time, by an almost complete absence of the
30-ms component. The N50 was the only component for which amplitude varied with
tonal frequency. Its amplitude was maximal at 750 Hz.
Left hemisphere The left-hand side of Figure 10.4 shows AEPs recorded from the left pri-
mary auditory cortex (leads 4 and 5) for different tonal frequencies. As was the case in the
right primary cortex, a triphasic N30/P45/N100 complex was observed. P45 and N100
amplitude recorded from the left hemisphere, however, did not vary as a function of
159220
200
180
160
140
120
100
80
60(^40) 250 Hz
100 μV
30 45 100
30 45 100
35 msec
200
180
160
140
120
100
80
60
40
500 Hz 600 Hz 750 Hz1 kHz 2 kHz 3 kHz 4 kHz
250 Hz 500 Hz 600 Hz 750 Hz1 kHz 2 kHz 3 kHz 4 kHz
Lead 4
Lead 5
A B Amplitude variation of the complex P45-N100
Figure 10.4 (A) Evoked responses recorded from the medial part of the primary auditory cortex (leads 4 and 5)
in the left HG. (B) Graphs representing amplitude variations for the P45/N100 complex according to different tonal
frequencies (ordinate axis: absolute amplitude expressed in V; abscissa axis: tonal frequency). The frequencies
vary from 250 Hz (first line) to 4 kHz (last line) (see comments in the text).