The indirect pathway is a circuit in the basal ganglia best-known for its hypothesized role in the inhibition of movement. In this video, I discuss how the structures of the indirect pathway are thought to work together to suppress unwanted movements.
For an article (on my website) that explains basal ganglia function, click this link: [ Ссылка ]
TRANSCRIPT:
The indirect pathway is a circuit in the basal ganglia hypothesized to play a role in the inhibition of movement. If you’re not already familiar with the direct pathway of the basal ganglia, you might want to watch my video on the direct pathway before you watch this video.
The indirect pathway model involves GABA neurons that project from the external segment of the globus pallidus to a region called the subthalamic nucleus. These globus pallidus neurons typically exert an inhibitory effect on glutamate neurons in the subthalamic nucleus, but when the indirect pathway is activated by signals from the cerebral cortex, this causes the activation of GABA neurons in the striatum, which project to the globus pallidus external and inhibit the activity of neurons there. This keeps the globus pallidus external neurons from being able to inhibit neurons in the subthalamic nucleus. The subthalamic nucleus neurons are activated by projections from the cortex, and they stimulate GABA neurons in the globus pallidus internal segment and substantia nigra pars reticulata. These GABA neurons in turn project to the thalamus, inhibiting thalamic neurons that travel to motor regions of the cerebral cortex to stimulate movement. The inhibition of these thalamic neurons thus inhibits movement. This activity in the indirect pathway is thought to antagonize the activity of the direct pathway and act to keep unwanted movements from occurring.
Neurons from the substantia nigra pars compacta travel to the striatum via the nigrostriatal pathway, and they can modulate the activity of the indirect pathway through dopamine release in the striatum. One effect of this seems to be the inhibition of activity in the indirect pathway, which leads to the facilitation of movement. This is thought to be one reason why dopamine depletion in disorders like Parkinson’s disease may lead to difficulties initiating movement.
References:
Mink JW. The basal ganglia: focused selection and inhibition of competing motor programs. Prog Neurobiol. 1996 Nov;50(4):381-425.
Purves D, Augustine GJ, Fitzpatrick D, Hall WC, Lamantia AS, Mooney RD, Platt ML, White LE, eds. Neuroscience. 6th ed. New York. Sinauer Associates; 2018.
Special thanks to Nicole Lookfong for help with fact-checking the script for this video.
