Cerebral Cortex Advance Access originally published online on April 13, 2005
Cerebral Cortex 2006 16(1):1-8; doi:10.1093/cercor/bhi090
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Feature Article |
Functional Significance of Olfactory-induced Oscillations in the Human Amygdala
1 INSERM U280, Mental processes and brain activation. 151 Cours Albert Thomas, 69003, Lyon, France, 2 Functional Neurology and Epileptology Department, Research Unit EA 1880, Neurological Hospital, Lyon, France and 3 Neurosciences and Sensory Systems Laboratory, Claude-Bernard University, Lyon, France
Address correspondence to Julien Jung, Mental Processes and Brain Activation, INSERM U280, 151 Cours Albert Thomas, 69003, Lyon, France. Email: jung{at}lyon.inserm.fr.
We recorded directly from the amygdalar nucleus of nine epileptic patients performing a delayed odor-matching recognition memory task. Time–frequency analysis of the responses to the odorants revealed that the stimulations elicited induced oscillatory responses, as well as already described olfactory evoked potentials. These oscillatory responses were composed of two frequency components — one in the beta band (15–25 Hz) and a faster one, in the low gamma band (25–35 Hz) — both of which lasted during the full duration of the inspiration. In pairs of identical odorants, the power of gamma oscillations was weaker for the second odorant (the target) than for the first one (the sample). We observed no such difference when the first and second odorants of a pair were different. Thus, gamma oscillations in the amygdala are weaker for repeated stimuli, a mechanism known as repetition suppression. This is consistent with an involvement of the human amygdala in the encoding and retrieval of olfactory information independently of its hedonic properties, at least in epileptic patients. Altogether, our results corroborate in humans evidence found in animals that oscillations serve as a common coding process of olfactory information.
Key Words: amygdala • oscillations • recognition memory • stereoencephalography • time–frequency analysis
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