| The basal ganglia are a collection of nuclei which have important roles in motor control and cognitive processing, and are the target of several human neurodegenerative disorders. The experiments described here examine the normal functioning of the basal ganglia by examining neural activity in the striatum (also termed caudoputamen, the major input structure of the basal ganglia). The thesis begins with a review of literature related to our current understanding of striatal function, with a special emphasis on the anatomy of the basal ganglia and striatum, the behavioral correlates of striatal neurons, and the function of the striatum in learning and memory. Experiments are then presented which address current issues in striatal function, including the identification of projection neurons and interneurons in extracellular recordings from awake, behaving rats, the behavioral correlates of striatal neurons in navigation tasks, and the representation of task parameters by ensembles of striatal neurons. On the basis of extracellularly recorded spike trains, neurons in the rodent striatum could be differentiated into phasic and tonic subtypes, which are believed to correspond respectively to projection neurons and interneurons of the striatum. Tonic neurons could be further differentiated into 3 subtypes on the basis of firing properties and extracellular action potential parameters, and may each correspond to distinct striatal neural types. Phasic neurons which were responsive during navigation tasks were active either during navigation or during reward-receipt. Tonic neuron subtypes were also behaviorally modulated: two subtypes showed spatial oscillations as rats were running in a sequential navigation task, while the third subtype was only modulated following the presentation of a cue which signaled food delivery. Ensembles of striatal neurons provided high-quality representations of task parameters such as spatial location and reward-delivery. However, a strong representation of space was only obtained in a sequential navigation task, and not in a navigation task in which spatial location was ambiguously associated with reward-delivery. Also, in the sequential navigation the striatal spatial representation developed with a time-course the preceded the development of a stable route through the environment, suggesting that the striatum may participate in developing a stable stimulus-response strategy in navigation. |
