Journal of neurophysiology
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Time-varying envelopes are a common feature of acoustic communication signals like human speech and induce a variety of percepts in human listeners. We studied the responses of 109 single neurons in the inferior colliculus (IC) of the anesthetized Mongolian gerbil to contralaterally presented sinusoidally amplitude-modulated (SAM) tones with a wide range of parameters. Modulation transfer functions (MTFs) based on average spike rate (rMTFs) showed regions of enhancement and suppression, where spike rates increased or decreased respectively as stimulus modulation depth increased. ⋯ The results suggest various possible mechanisms that could create IC MTFs, and strongly support the idea that inhibitory inputs shape the rMTF by sharpening regions of enhancement and creating a suppressive region. The paucity of BMFs above 100 Hz argues against simple rate-coding schemes for pitch. Finally, any labeled line or topographic representation of modulation frequency is unlikely to be independent of SPL.
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The effects of dopamine (DA) on a persistent Na(+) current (I(NaP)) in layer V-VI prefrontal cortical (PFC) pyramidal cells were studied using whole cell voltage-clamp recordings in rat PFC slices. After blocking K(+) and Ca (2+) currents, a tetrodotoxin-sensitive I(NaP) was activated by slow depolarizing voltage ramps or voltage steps. DA modulated the I(NaP) in a voltage-dependent manner: increased amplitude of I(NaP) at potentials more negative than -40 mV, but decreased at more positive potentials. ⋯ This was associated with a shift in the start of nonlinearity in the slope resistance to more negative membrane potentials. We proposed that this effect is due to a D1/D5 agonist-induced leftward shift in the activation of I(NaP). This enables DA to facilitate the firing of PFC neurons in response to depolarizing inputs.