Thalamocortical dynamics of rhythmic selective and tonic suppressive modes in the auditory system

TitleThalamocortical dynamics of rhythmic selective and tonic suppressive modes in the auditory system
Publication TypeConference Paper
Year of Publication2014
AuthorsLakatos, P., Barczak A., Neymotin S. A., Lytton WW., Mcginnis T., Javitt D. C., & Oconnell M. N.
Conference NameSociety for Neuroscience 2014 (SFN '14)
KeywordsSFN, Society for Neuroscience

Earlier studies provide plenty of evidence that when attention is directed towards a given modality, the amplitude of alpha oscillations increases in regions processing stimuli of ignored modalities. At the same time we also have evidence that ongoing oscillations are reset and - if stimuli are rhythmic - entrained by attended stimuli, even in primary cortical areas processing ignored modality information. The main goal of the present study was to investigate how these two different aspects of brain operation co-exist in the auditory thalamocortical system in non-human primates. By examining dynamic changes in layer-specific neuronal ensemble activity of primary auditory cortex (A1), we identified discrete cortical operational modes (mesostates) in two subjects performing an intermodal selective attention task. We then characterized the thalamaocortical dynamics of these mesostates in two additional subjects. For all subjects, neuroelectric activity was recorded simultaneously using two linear electrode arrays positioned either in corresponding A1 regions of the two hemispheres, or auditory thalamic regions and ipsilateral A1. As expected, alpha amplitude in A1 was significantly larger in trial blocks where monkeys were attending to visual stimuli, especially in the granular layer. We also found significant entrainment to attended rhythmic visual stimuli in the supragranular layers. When we examined the temporal evolution of these two distinct operational modes, we found that they were anticorrelated: in time periods of large amplitude granular layer alpha oscillatory activity, entrainment of ongoing delta-theta oscillations to the visual stimuli ceased in the supragranular layers. In some trial blocks, the amplitude of alpha oscillations waxed and waned rhythmically at a 0.02 Hz rate both in auditory cortex and in some of the thalamic structures examined. Our results indicate that the brain uses two distinct strategies for different degrees of stimulus suppression in the ignored sensory modality. Inputs related to these stimuli are either 1) suppressed tonically by a mechanism that is characterized by high amplitude thalamocortical alpha oscillatory activity, or 2) rhythmic excitability fluctuations are aligned to the timing of attended stimuli via entrainment. In the latter mode, responses to inputs that are synchronized with attended-modality events are actually enhanced while attention has no effect on other inputs, which allows ignoring these. We suggest that this rhythmic selection mode provides the substrate to solve the cocktail party problem, where the selection of a relevant auditory stream is greatly enhanced by using visual cues.