femme Neuroscience Notes

Some Topics

Basal Ganglia

The cerebral hemispheres sit over clusters of neurons that are essential to animal life. The central clusters are referred to as thalami and the lateral clusters are referred to as basal ganglia. The names are old and obsolete but, because they are imbedded in all neuroscience descriptions, perservation overrides innovation. The striatum includes the caudate nucleus and the putamen. The name describes the striated appearance created by myelinated axons passing among clusters of neurons. The neocortex sends converging inputs to the striatum. Motor neurons project to the spines of the spiny neurons using glutamate as the neurotransmitter. Nigrostriatal neurons synapse on the spine shafts. Other inputs come from the thalamus, the subthalamic nucleus and the globus pallidus.

There abundant examples of movement disorders that emerge when components of the basal ganglia are damaged. Involuntary movements include tremors (rhythmic, oscillatory movements), athetosis (slow, writhing movements), chorea (abrupt movements of the limbs and facial muscles), ballism (violent movements), and dystonia (persistent postures, grotesque movements and postures).

Huntington's disease is a genetic disorder that caused by loss of striatal neurons with decreased output of the basal ganglia to the thalamus The result is hyperkineticity, involuntary movements associated with a form of dementia that features reduced ability to plan and execute routine tasks, slowed thought, and impaired judgment.

The intriguing feature of these old modules is that they do not control movement directly by sending signals through the brain stem and spinal cord. They are recursively wired to neurons in the thalamus and cerebral cortex. When you recognize that all interaction with the outside is accomplished by movement, and the cognition is a collection of abilities that link the outside to the inside, you might appreciate that that the basal ganglion and thalamus play a central role in cognition.

You can argue that innate features of all animals that persist in humans are produced by the inborn structure and fixed functions of the basal ganglia, thalamus and limbic system working together to link inside and outside. The cerebral cortex adds sophisticated sensing and learning capabilities that can direct but not supersede innate behaviors.

For example, Cohen et al stated: “We found that personality characteristics are linked to dissociable connectivity streams in the human brain. Activity between a subcortical network, including the hippocampus and amygdala, and the ventral striatum predicted individual differences in novelty seeking; tracts between prefrontal cortex and the striatum predicted individual differences in reward dependence. These findings suggest that the strength of limbic-striatal connectivity may, in part, underlie human personality traits.”

See Reptilian Brain