The human amygdala. I. Electrophysiological responses to odorants.

Nine patients had an amygdalotomy for attempted relief of intractable seizures and, as an aid for localization, recordings were made from the amygdala and later computer analyzed. The background activity is 3-18 c/sec; in response to odorants sinusoidal bursts are seen, synchronous with inspiration at 12-24 c/sec, but mainly 40-70 c/sec. Each odorant is associated with a given group of frequency components. However, for many different odorants the number of these components is restricted and the hypothesis is presented that odor discrimination in man's amygdala is not determined by which components are present, but the patterning of the components according to their amplitude. Odorants within the same odor class produced similar patterns of response. Epileptiform activity was recorded in two different forms, one in response to odors, similar in frequency to the slower bursts, except for sharper configurations, at times progressing to clinical seizures and the second as an insertion discharge from an advancing electrode, similar in frequency to the faster bursts. These latter data suggest that the repertoire of a given neural system or structure may be limited to specific frequencies but the configuration or patterning of these frequencies define the different states of the structure.