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.
When you recognize that all interaction with the outside is accomplished by
movement, 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.”
[i] Michael Cohen, Jan-Christoph
Schoene-Bake, Christian E Elger & Bernd Weber. Connectivity-based segregation of
the human striatum predict. personality characteristics. Nature Neuroscience 12,
32 - 34 (2008) Published online: November 2008 | doi:10.1038/nn.2228
