[A Role of the Basal Ganglia in Processing of Complex Sounds and Auditory Attention]

A hypothetical mechanism is suggested for processing of complex sounds and auditory attention in parallel neuronal loops including various auditory cortical areas connected with parts of the medial geniculate body, inferior colliculus and basal ganglia. Release of dopamine in the striatum promotes bidirectional modulation of strong and weak inputs from the neocortex to striatal neurons giving rise to direct and indirect pathways through the basal ganglia. Subsequent synergistic disinhibition of one and inhibition of other groups of thalamic neurons by the basal ganglia result in the creation of contrasted neuronal representations of properties of auditory stimuli in related cortical areas. Contrasting is strengthened due to a simultaneous disinhibition of pedunculopontine nucleus and action at muscarine receptors on neurons in the medial geniculate body. It follows from this mechanism that involuntary attention to sound tone can enhance an early component of the responses of neurons in the primary auditory cortical area (50 msec) in the absence of dopamine due to a disinhibition of thalamic neurons via the direct pathway through the basal ganglia, whereas voluntary attention to complex sounds can enhance only those components of responses of neurones in secondary auditory cortical areas which latencies exceeds latencies of dopaminergic cells (i.e. after 100 msec). Various consequences of proposed mechanism are in agreement with known experimental data.