InAuKa

InAuKa        

 

Priority Programme: Resolving and Manipulating Neuronal Networks in the Mammalian Brain - from Correlative to Causal Analysis

Interareal phase coherence as a mechanism for attention-dependent neuronal signal routing: A model-guided causal analysis using new, multi-contact floating silicon probes for intracortical chronic stimulation and recording in primates

Prof. Dr. Andreas Kreiter

Dr. Udo Ernst

Prof. Dr. Walter Lang

 

The brain consists of large neuronal networks that are densely inter-connected. Depending on context, task and selective attention, sub-networks become selected such that specific computations are performed, which ultimately lead to appropriate behavioural output. Thereby sensory signals become selectively channelled through the brain. The latter is particularly evident in the visual system during selective attention. In higher areas of visual cortex as V4, the responses of neurons with several stimuli in their receptive fields were shown to be similar as if only the attended stimulus would be present. Last not least, in a recent experiment we employed behaviourally irrelevant random modulations of stimulus contrast as a direct method to explore the properties of signal routing by attention through visual areas. In particular we found that attention suppresses the contribution of the non-attended stimuli to the responses in V4 while it opens a specific frequency limited channel for the attended location.

 

These findings together pose a challenge to our understanding of the gating mechanisms in the brain. While the above mentioned experimental results are consistent with the hypothesis, that coherent oscillations might underlie the selective routing of information through cortex, there is still no model available that captures and integrates all relevant experimental results. In particular, it is still not decided if synchronization is in fact causally involved in the gating mechanism or rather an epiphenomenon reflecting increased coupling.

 

In this project we join as neurobiologists, theorists and engineers to attack these questions. To improve experimental access to and control of the networks under investigation we will in parallel develop, test and use a fully implantable, virtually force-free floating multi-contact electrode needle array for chronic intracortical recording and stimulation in the primate cortex. This will allow high resolution electric and visual stimulation as causal instruments to directly manipulate mechanisms putatively underlying the attention dependent selective processing of behaviourally relevant input signals as well as the effective suppression of behaviourally irrelevant signals. The new tools and methods will be established to directly influence different aspects of the dynamics of the cortical networks during attentive processing of visual stimuli by electrical stimulation. Simultaneously the gated signal channels can be characterized continuously by task-irrelevant contrast modulations. This will allow us to critically test the hypothesis that gamma-band synchronization serves as gating mechanism for attention dependent routing of information. Furthermore, the results will serve to characterize the fundamental properties of the network’s dynamic properties and will be used to build realistic models for the proposed routing mechanisms.