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CCN Special Seminar

Wednesday, December 13, 2017,

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  • Location: Wilson Hall • 111 21St Ave S • Nashville, TN 37240
  • Room: Room 316

Dr. Salva Ardid, Boston University

Title: Brain mechanisms supporting context-dependent decision making

Summary: Biased competition (BC) is an important brain mechanism that guides context-dependent decision making. BC refers to an input bias that breaks the symmetry between competing neuronal ensembles that are physiologically identical. It has not been explored systematically if BC can also be mediated between physiologically distinct neuronal ensembles receiving the same input. In my talk I will focus on a circuit model of corticostriatal processing because the striatum fulfills the two conditions for BC under such “balanced input”: striatal D1 and D2 medium spiny neurons (MSNs) represent two distinct populations that receive balanced cortical input. Hence, unraveling the mechanisms of BC under balanced input is critical for understanding how the basal ganglia selects between GO and NO-GO actions.  Results from our model identify three distinct BC mechanisms that flexibly bias either population: (1) The “rate coding” mechanism: which MSN type (D1 or D2) shows higher firing rate depends on input strength (high or low). (2) The “coherence coding” mechanism: under rhythmic input of high strength , each MSN type is more synchronized at a distinct input frequency. (3) The “parallel coding” mechanism: under rhythmic input of low strength, D2 MSNs show higher firing rate, but D1 MSNs fire more coherently. Therefore, biases of the two neural codes (rate and coherence) run in parallel, and the properties of the downstream readout determine which of the two is functionally relevant.  Finally, I will show that from the three candidates, only the “coherence coding” mechanism is fully consistent with the current interpretation of rhythmic activity supporting rule-based decisions reported in prefrontal cortex.