Research

 

Basal ganglia function

Sketch of basal ganglia pathways that contribute to the execution and suppression of actions (from Schmidt et al., 2013). STR: striatum; SNr: substantia nigra (pars reticulata); STN: subthalamic nucleus.

The basal ganglia are a set of subcortical structures that make important contributions to motor control. We are interested in specifying these contributions and understanding the underlying neural mechanisms. For example, we studied neural activity in multiple basal ganglia structures in rats performing a stop-signal task (Schmidt et al., 2013). Subthalamic nucleus neurons showed low latency responses to Stop cues, irrespective of whether actions were successfully canceled or not. By contrast, neurons downstream in the substantia nigra (pars reticulata) responded to Stop cues only when actions were successfully suppressed. Remarkably, nigral neurons with fast Stop cue responses formed a functionally-defined ‘hotspot’ that corresponds to the anatomically-defined nigral “dorsolateral core” region. Recordings and computational modeling together indicate that sensorimotor gating of the stop cue arises in the hotspot from the relative timing of two distinct inputs to the substantia nigra: cue-related excitation from the subthalamic nucleus and movement-related inhibition from the striatum.

Dopamine

Dopamine is a neurotransmitter with complex, not well-understood effects. In the basal ganglia dopamine modulates cortical input to the striatum. We study the functional role of dopamine with computational models ranging from `low-level’ cellular models, over neural network models to `high-level’ reinforcement learning models. The goal is to understand how dopamine contributions to learn selecting good action (e.g. via synaptic plasticity) as well as the actual execution of actions (e.g. by changing motivational aspects of behavior). We apply our research result to clinical scenarios including Parkinson’s disease to study how pathological dopamine levels affect behavior.

Beta oscillations

While, beta oscillations are prominent in patients with Parkinson’s disease, they also occur in healthy animals. One circuit where beta oscillations are generated includes the globus pallidus and the subthalamic nucleus. We study the neural mechanisms that lead to beta oscillations and also potential functions that beta oscillations have in the processing of information. In previous work we have found that beta oscillations occur when sensory cues are utilized for behavior (Leventhal et al., 2012), suggesting a functional role of beta oscillations in sensorimotor processing. To further specify function and mechanisms of beta oscillations, we generate large-scale network simulations of basal ganglia circuits in healthy and pathological scenarios.

 

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