Final answer:
The activity of the cerebral cortex determines the excitation or inhibition of thalamic motor nuclei for action selection. The basal nuclei, processing cortical inputs, modulate this thalamic activity, influencing motor commands. The basal nuclei's indirect pathway decreases cortical motor activity as it affects the thalamus.
Step-by-step explanation:
The excitation or inhibition of thalamic motor nuclei, which leads to action selection, is primarily determined by the activity of the cortex. The cerebral cortex sends information to the thalamus, influencing the effects of the basal nuclei. These basal nuclei receive input from the cortical areas and compare it with the individual's general state through the activity of a dopamine-releasing nucleus. The output from the basal nuclei affects the thalamic activity that increases or decreases cortical activity, thereby resulting in changes to motor commands. Subcortical nuclei, including the basal forebrain and the limbic system, also play roles in this modulation, affecting attention, memory, emotion, and coordination.
The basal nuclei have two pathways that process information within the cerebrum. The indirect pathway results in decreased cortical activity and less motor activity due to the disinhibition of the subthalamic nucleus, with a consequential effect on the thalamus and movement initiated by the cerebral cortex.
Components of the forebrain like the thalamus, hippocampus, and amygdala are involved in various functions. For instance, the thalamus also assists in coordinating head and eye movements during tasks such as catching a ball, highlighting its role in motor control beyond action selection.