Objective

To study activity of auditory cortex reflected by the N100 and P200 components of the auditory evoked potentials during memorization and scanning of short-term memory stores.

Methods

In a MEMORY task subjects classified a probe digit either as a member or not a member of a previously presented list of digits that varied in size from one, 3, 5 and 7 items. For comparison, subjects in a NUMBER task listened to a list of digits as in the MEMORY task but determined only whether the probe digit as odd or even. Evoked potentials to the presentation list and to probes were recorded from scalp electrodes and separately averaged for both tasks. The components peaking at approximately 100 ms (N100) and 200 ms (P200) that reflect activity of primary auditory cortex were identified and peak amplitudes and latencies were measured.

Results

For presentation set items, the amplitude of N100 was affected by set size in the MEMORY but not in the NUMBER task; N100 was larger for the one item set than for the 3, 5, and 7 item sets. P200 increased in amplitude in a linear manner for both the MEMORY and NUMBER tasks. For probe items, N100 but not P200 amplitude decreased in a linear manner as the number of items in the presentation set increased in the MEMORY but not in the NUMBER task. The linear change of N100 amplitude during memory scanning was particular to inset but not to out-of-set probes. The amplitudes of both N100 and P200 were almost twice as large in probe digits than in the digits in the presentation set in both the MEMORY and NUMBER tasks.

Conclusion

Auditory sensory cortical activity in humans during an auditory short-term memory task shows dynamic changes during both memorization and memory scanning.