The basal ganglia system as an engine for exploration

One of the earliest attempts at building a theory of the basal ganglia (BG) is based on the clinical findings that lesions to the direct and indirect pathways of the BG produce quite opposite motor manifestations (Albin et al., in Trends Neurosci 12(10):366–375, 1989). While lesions of the direct pathway (DP), affecting particularly the projections from the striatum to GPi, are associated with hypokinetic disorders (distinguished by a paucity of movement), lesions of the indirect pathway (IP) produce hyperkinetic disorders, such as chorea and tremor. In this chapter, we argue that describing the two BG pathways as having mutually opponent actions has limitations. We argue that the BG indirect pathway also plays a role in exploration. We should evidence from various motor learning and decision-making tasks that exploration is a necessary process in various behavioral processes. Importantly, we use the exploration mechanism explained here to simulate various processes of the basal ganglia which we discuss in the following chapters.