The hyperdirect pathway through the basal ganglia

Hyperdirect switching pathway from the cortex through the basal ganglia towards the thalamus

Response inhibition

The "hyperdirect pathway" through the basal ganglia towards the thalamus starts from the cerebral cortex of the frontal lobes (especially the MC, SMC and PMC areas) and, after switching in the subthalamic nucleus (STN), runs directly into the GPi-SNr.

In short, it can be said that activity along the "Hyperdirect Pathway" involves an admittedly very short, but nevertheless, interruption in the ongoing motor signaling from the cerebral cortex to the brain stem and spinal cord.

The signals from the cerebral cortex along the hyperdirect pathway excite STNs, which in turn excite the inhibitory GPi-SNr. The effect is a very strong and short-term slowing of the thalamic nuclei that drive on the motor areas of the cerebral cortex. The running movement program is discontinued. The response inhibition allows a new movement program to be immediately selected and executed using activity along the "Direct Path".

The nerve impulse flows along the hyperdirect, direct and indirect pathways are intertwined and coordinated from SNc; Substantia Nigra, pars compacta.

Note that if STN ceases to function, all excitation of GPi-SNr lapses. GPi-SNr is then completely at the mercy of the "direct road" braking impact. The effect is that GPi-SNr's own brake and control of affected thalamus nuclei decreases. The nuclei are disinhibited and "flood" motor parts of the cerebral cortex with excitatory signals. As a result, non-coordinated movement programs begin to be continuously delivered to the motor neurons of the brainstem and spinal cord within the opposite half of the body.
Cf. HemiballismNambu A., Tokuno H., Takada M. (2002) Functional significance of the cortico-subthalamo-pallidal hyperdirect pathway. Neuroscience Research 43, 111-117
Jahfari S. et al. (2011) Effective Connectivity Reveals Important Roles for Both the Hyperdirect (Fronto- Subthalamic) and the Indirect (Fronto-Striatal-Pallidal) Fronto-Basal Ganglia Pathways during Response Inhibition. The Journal of Neuroscience 31, 6891–6899.