Life Sciences G13
Title: Theory of reinforcement learning and motivation in the basal ganglia
This talk will suggest a simple mathematical description of how subcortical circuits in the basal ganglia select actions on the basis of past experience and the current motivational state. According to the presented theory, the basal ganglia evaluate the utility of considered actions by combining the positive consequences (e.g. nutrition) scaled by the motivational state (e.g. hunger) with the negative consequences (e.g. effort). The theory proposes how the basal ganglia compute utility by combining the positive and negative consequences encoded in the synaptic weights of striatal Go and No-Go neurons, and the motivational state carried by neuromodulators including dopamine. Furthermore, the theory suggests how the striatal neurons learn separately about payoffs and costs of actions. The model accounts for the effects of dopaminergic modulation on behaviour, and patterns of synaptic plasticity in striatum.
May, 18th – Simon Thorpe ( CerCo UMR 5549, CNRS-UT3)
May, 25th – Katarina Kolaric (University of Bristol)
The function of mossy cells in the dentate gyrus of the hippocampus, and their role in pattern separation memory, is still largely unknown. In this talk, I will present my PhD work, which investigated the role of mossy cells in the local dentate gyrus circuit using immunohistochemistry, in vitro electrophysiology and computational modelling techniques. Moreover, I will discuss how mossy cells are implicated in pattern separation memory by presenting behavioural data from a transgenic mouse model that specifically lack mossy cells. Finally, I will give a brief overview of my current work at the Integrative Epidemiology Unit (IEU), where I use Mendelian Randomisation as a method to detect potential risk factors in the human population for cognitive decline and Alzheimer’s Disease.
One prominent feature of Parkinson’s disease is the emergence of correlated activity in basal ganglia output neurons. In contrast, in healthy animals, the activity in basal ganglia output regions is usually uncorrelated, potentially due to “active decorrelation”. We investigated the effect of correlations among basal ganglia output neurons on the transmission of motor signals via rebound spikes in a Hodgkin-Huxley model of a thalamocortical neuron. We found that correlations in the basal ganglia output decrease the signal-to-noise ratio in the transmission of motor signals to the thalamus, potentially related to the emergence of motor symptoms in Parkinson’s disease. In addition, our model indicates that thalamocortical neurons may be a key site for the integration of sensory and motor signals.
June, 8th – Adam Packer (University of Oxford)
Neural circuits display complex spatiotemporal patterns of activity on the millisecond timescale during behavior. Understanding how these activity patterns drive behavior is a fundamental problem in neuroscience, and remains a major challenge due to the complexity of their spatiotemporal dynamics. The ability to manipulate activity in genetically defined sets of neurons on the millisecond timescale using optogenetics has provided a powerful new tool for making causal links between neuronal activity and behavior. I will discuss novel approaches that combine simultaneous two-photon calcium imaging and two-photon targeted optogenetic photostimulation with the use of a spatial light modulator (SLM) to provide ‘all-optical’ readout and manipulation of the same neurons in vivo. This approach enables reading and writing of activity in neural circuits with single-cell resolution and single action potential precision during behavior. I will describe the power, limitations and future potential of this approach; and discuss how it can be used to address many important problems in neuroscience, including transforming our search for the neural code and the links between neural circuit activity and behavior.
June, 15th – Tamar Makin (University of Oxford)