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 Neuroprostheses

 Projects

(A) Physiological correlates of learning in the auditory cortex

Our most traditional research topic is the study of physiological correlates of learning in the auditory cortex. We perform recordings of spike activity in multiple single units and of local field activity from the auditory cortex of Mongolian gerbils who perform in learning tasks, such as classical or discriminative conditioning, or cognitively more demanding tasks, such as category learning and concept formation.

Using classical receptive field analysis we have described several features of learning-induced receptive field plasticity that indicate a complex reshaping of receptive fields rather than a simple change of a unit's best frequency. The functional implication of this plasticity is therefore a redefinition of the unit's role in a complex network rather than a simple "retuning". One identified functional aspect of this new role is an increase of spectral contrast sensitivity which is expressed in learning-induced increases of local slope in a unit's isointensity response function (e.g. Ohl and Scheich, 1996, 1997b, 2005).

(B) Development of an interactive sensory cortical neuroprosthesis

From using electrical stimulation of the brain as a tool (complementing recording and lesioning) for studying relationships between brain activity and phenomena of behaviour and perception, we have recently moved to using intracortical microstimulation as a potential conveyor of information in form of a sensory neuroprosthesis, i.e. a brain machine interface that operates with the brain in the "writing mode" rather than in the "reading mode" as the recently so successful motor prostheses do. We so far have achieved a proof of principle of a sensory cortical neuroprosthesis for the auditory cortex. The feasibility of such a system (as opposed to the more simple motor cortical prostheses) relies on using an interactive approach (" communication approach " between device and brain) rather than a unidirectional operation (" coding approach " used in peripheral neuroprostheses like the cochlear implant). We continue this work in the next years and expect significant progress for both the construction of neuroprostheses and basic research on functional circuitry of mammalian sensory cortex.

(C) Feature interference during selective attention

We have recently set up (in collaboration with Peter Heil and Heinrich Neubauer ) a laboratory for scalp EEG measurements on human subjects. Here we collaborate with C. v. Leeuwen, BSI RIKEN, Japan , and T. Lachman, Universität Bamberg, on the interference of object features during a selective attention task in humans using EEG. Our focus is on the comparison of within-trial interference effects (e.g. Stroop interference) and between-trial interference effects (e.g. Garner interference) to test ideas about the nature of neuronal processes leading to perception of complex stimuli as a whole. We use this project also to bridge the unfortunate gap between animal and human research on neurodynamics. We believe that research on both systems in parallel will be necessary and fruitful for both disciplines.

(D) Interaction of bottom-up and top-down processes in auditory perception

This project is our contribution to the Sonderforschungsbereich Transregio 31 "Das aktive Gehör" supported by the Deutsche Forschungsgemeinschaft (DFG). On the basis of our previous work on phenomenological aspects of both bottom-up processing (classical work on "coding") and top-down-processing (our work on learning-induced changes on spectrotemporal receptive fields in auditory cortex) we aim at a biophysically rooted mechanistic understanding of the interaction of both types of processes. By "understanding" we mean the setting up of a (mathematically concrete) model of this interaction which is explicit with respect to both the neural systems and physiological interactions involved, as well as the neuronal operations (in the sense of computational neuroscience) carried by them.

(E) Mechanisms of reward evaluation and decision making

We are currently repeating a number of classic behavioral experiments (including those utilizing intracerebral electrostimulation) on reward evaluation and biasing of decision making in our animal model with the aim of combining those with electrophysiological recordings in various brain systems for testing certain hypotheses we have about the nature of these processes.

(F) Mechanisms of crossmodal plasticity

In this project planned for the near future we will investigate biophysical mechanisms underlying audio-visual integration and audio-visual learning plasticity. We perform multichannel recordings in auditory and visual cortex in awake behaving gerbils and use directed coherence and phase correlation (based on the Hilbert transform) analysis for the continuous data and pattern statistics for the spike data.

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