Abstract
We have studied magnetic and electrical fields of the brain in normal subjects during the performance of an auditory verbal short-term memory task. On each trial 3 digits, selected from the numbers ‘one’ through ‘nine’, were presented for memorization followed by a probe number which could or could not be a member of the preceding memory set. The subject pressed an appropriate response button and accuracy and reaction time were measured. Magnetic fields recorded from up to 63 sites over both hemispheres revealed a transient field at 110 ms to both the memory item and the probe consistent with a dipole source in Heschl's gyrus; a sustained magnetic field between 300 and 800 ms to just the memory items localized to the temporal lobe slightly deeper and posterior to Heschl's gyri; and a sustained magnetic field between 300 and 800 ms to just the probes localized bilaterally to the medio-basal temporal lobes. These results are related to clinical disorders of short-term memory in man.
Highlights
Studies of short-term memory in man reveal that the time required for scanning the contents of the short-term store increases linearly as the number of items memorized increases and that the entire memory store is scanned before a response is made 25'26
During the scanning of the short-term memory store, a positive potential appears over the midline, maximal in the parietal region, which is independent of the modality or type of stimulus 18
The results of this study, using measures of both electrical and magnetic fields, show a sequence of brain activity extending over approx, one second during the memorization and recall of digits presented acoustically in a paradigm that engages short-term memory processes 26
Summary
Studies of short-term memory in man reveal that the time required for scanning the contents of the short-term store increases linearly as the number of items memorized increases and that the entire memory store is scanned before a response is made 25'26. There is consensus that, in man, verbal short-term memory for auditory items is superior to that for visual items and that lesions in the left parietotemporal region severely impair auditory verbal short-term memory 28. During the scanning of the short-term memory store, a positive potential appears over the midline, maximal in the parietal region, which is independent of the modality or type (verbal or nonverbal) of stimulus 18. These results suggest that different areas of the brain are active during memorization versus scanning
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