Following neuronal signals of multiple visual stimuli through cortical pathways to identify attentional gating mechanisms

• Applicant: Professor Dr. Andreas K. Kreiter
• Subject Area: Cognitive, Systems and Behavioural Neurobiology
• Term: from 2017 to 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 331514942

Processing of natural scenes requires the visual system of our brain to handle a large number of independent visual stimuli at the same time. Often they are located close together in the retinal image. As a consequence of strong divergence and convergence of neuronal connections along the visual processing pathways, neurons typically receive signals originating from more than one visual stimulus. Nevertheless, neurons are capable to process selectively one of those stimuli if selective attention is directed to this stimulus. They are capable to respond as if only the attended stimulus would be present and suppress the often more numerous and stronger signals from other stimuli. While such attention-dependent selective stimulus processing is well documented, the underlying neuronal mechanisms are not well understood and discussed controversially.Previous results from our lab and others suggest, that this remarkable capability can be explained by attention-dependent gating mechanisms. They allow the appropriate subset of a neuron's input signals that encode the attended stimulus to pass. In contrast, all other input signals are suppressed. This gating can be explained by two major types of mechanisms. The so called asynchronous mechanisms assume, that specific circuitry interferes in an attention-dependent manner with signal delivery, e.g. by modulating synaptic transmission or canceling excitatory signals with matched inhibitory input. On the other hand, synchronous mechanisms imply specific spatio-temporal activity patterns modulating the transmission of signals, between the signal receiving neurons and the afferent input. The behaviorally relevant inputs oscillate synchronously with the signal receiving neurons in the gamma-band (30 - 100 Hz) and with a specific phase difference, allowing for optimal signal transmission. The activity patterns of all other inputs avoid this specific phase relation and are therefore rather suppressed. We have previously demonstrated corresponding patterns of attention dependent synchronization, but it is not known whether they are responsible for signal gating or rather epiphenomenal.Major goal of the project is to investigate, whether attention-dependent gating results from an asynchronous or a synchronous mechanism. Using a method we developed previously, we will tag the neuronal signals of individual stimuli. This will allow to follow the flow of information between visual cortical areas and to observe whether occasional deviations from the optimal phase are associated with reduction of transmission of signals from the attended stimulus. The results will strongly support the synchronous gating mechanism if signal transmission depends indeed strictly on phase relations. If fluctuations of signal transmission turn out to be phase-independent, the hypothesis of a synchronous mechanism has to be rejected in favor of an asynchronous mechanism.

• DFG Programme: Research Grants