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Nile Graddis presents his study at the Mary Gates Undergraduate Research Symposium

Nile Graddis will present his work during the poster presentation of the Mary Gates Undergraduate Research Symposium.  Nile's abstract is reprinted below.

Phasic Dopamine Release Inhibits Hippocampal Gamma Oscillations


·         Nile Graddis, Junior, Psychology Mary Gates Scholar


·         Sheri Mizumori, Psychology

·         Marsha Penner, Psychology

Learning and memory require that neural activity be flexibly organized. Neurons must sometimes fire together in ensembles so that important signals are not lost in the complex activity of the brain, but these ensembles must also be capable of forming, breaking apart, or reforming at a moment’s notice. Such transient synchrony of neural activity may be achieved by means of oscillatory firing. Oscillatory firing at various frequencies is commonly found in electrophysiological recordings from the brain and may underlie the dynamic organization of neural activity. We investigated oscillatory activity in a brain region critical to learning and memory, the hippocampus. The power of oscillatory activity in the hippocampus at several frequency bands including gamma (30-80 hz) has been linked to successful encoding and recall in hippocampus-dependent memory tasks. Prior work has also shown that inputs from the ventral tegmental area are necessary for normal hippocampal function and for spatial learning and memory. These inputs occur in two forms: tonic baseline firing and intermittent phasic bursts. We tested genetic knockout mice that lack phasic but not tonic inputs from the ventral tegmental area while animals foraged for food on a spatial navigation task. We simultaneously recorded local field potentials in the hippocampus, which represent the net inputs to a region of the brain and allow us to assess the power of oscillatory activity. In the preliminary data, knockout mice demonstrated more rapid learning in response to successive manipulations of the reward location compared to controls. Knockouts also showed higher gamma-frequency but not theta-frequency (4-10 hz) power. These results suggest that phasic inputs from the ventral tegmental area selectively inhibit gamma-frequency oscillations in the hippocampus. This role may be behaviorally relevant, reflecting the possibility that these oscillations play a role in organizing learning and memory.