Action Potential

I find the article by Williams and Eskandar both interesting and intriguing ina number of ways. Both the function and the dysfunctions of the basal ganglia are matters of significant interest. A couple of questions and thoughts came to my mind while reading the article:

Based on traditional views of basal ganglia function, one would suspect that the putamen should have a prominent role in acquisition of basic sensory-motor associations. The cortico-striatal loops through the basal ganglia are considered to be segregated to a large extent, respecting the topological layout of the origins cortical projections, frontal regions projecting to caudate and posterior association areas to the putamen (of course, I should check the anatomical references cited in the paper). In this study, caudate activity was primarily was strongly associated with feedback, while activity of putamen neurons closely tracked the learning curve, suggesting that putamen is a candidate for the locus of the memory for the stimulus-response associations. In the context of what is known about the wiring of basal ganglia circuits, through which pathway(s) is feedback-related activity caudate likely to have a guiding influence on the putamen?

While a number of computational models have addressed the nature of the neural computations subserved by striatal networks, so far as I am aware, existing models do not predict directly that stimulation of the caudate nucleus should facilitate l visuo-motor association learning. It will be interesting to see how models of basal ganglia function will accommodate the current findings

I am aware of Graybiel and her colleague’s work involving tonically active neurons in striatal matrisomes, and their role in mediating reward-based learning in striosomes containing the phasically active medium spiny neurons. The current report focuses on the spiny neurons, but could it be the case that the critical effect of microstimulation is on the activity of tonically active neurons?

As a closing remark, human neuropsychological studies have revealed that learning of stimulus-response associations is impaired in Parkinson’s and Huntington’s patients (one could cite Knowlton and her colleague’s work). To my knowledge, surgical interventions and implantation of neural stimulators to alleviate the symptoms of PD target primarily the globus pallidus and the subthalamic nucleus. Perhaps the findings of this study will have implications for treatment of Parkinson ’s disease.