The basal ganglia and cognition
The basal ganglia are a collection of subcortical structures that were traditionally viewed as only being involved in movement. The basal ganglia include the caudate, globus pallidus, putamen, and nucleus accumbens (the subthalamic nucleus and the substantia nigra are also often included as part of the basal ganglia). Scientists have known about the basal ganglia’s role in movement for a number of years but have only recently really started studying their role in cognition, executive function, and memory.
Dissections of the brain have shown that there are a number of white matter “loops” exiting and entering the basal ganglia. We know that the striatum, which consists of the putamen and the caudate and is so named because there are connections between the two structures that look like stripes (striations), receives excitatory input from all over the cortex (Seger & Cincotta, 2002). The prefrontal cortex (roughly the very front of the brain) connects to the anterior putamen and the head of the caudate but the tail of the caudate and the posterior parts of the putamen receive inputs from parts of the temporal and parietal lobes. The frontal lobes are involved in tasks such as planning, remembering, organizing, and many other of the “higher-order” cognitive abilities. The parietal lobes are involved in visuo-spatial tasks and the temporal lobes are involved in memory and object recognition (these are gross simplifications of lobular function – all lobes have more functions than I wrote about). So if parts of the basal ganglia receive inputs from the frontal lobes, what are the basal ganglia doing if not just moderating movement?
Seger and Cincotta (2002) demonstrated that the striatum is involved in a type of learning. Lamar, Price, Libon, Penney, Kaplan, Grossman, and Heilman (2007) demonstrated that dementia patients with higher levels of white matter disruption (which likely interferes with basal ganglia connectivity) have poorer working memory performance. One example of what working memory is is performing a multiplication task in your head without using any paper – having to remember the digits and manipulate them is a process of working memory. Benke, Delazer, Bartha, and Auer (2003) reported on two clinical cases of patients with hematoma disrupting the left basal ganglia. Both patients had “executive function” disruption, short- and long-term memory impairment, and attentional difficulties. Many other researchers have demonstrated the role the basal ganglia has in cognition but we are still in the early stages of this area of research.