Regions of the Frontal Lobes
1. Primary Motor Cortex (M1, Brodmann area 4):
The primary motor cortex is located on the
precentral gyrus just rostral to the central sulcus. It is
the source of cortical neurons that will project to the
brainstem and spinal cord to activate neurons
involved in the control of voluntary movements. It
receives input from the neighboring primary
somatosensory area (S1, on the postcentral gyrus)
and premotor cortex, as well as from the ventral
lateral nucleus of the thalamus (a relay nucleus with
projections from the cerebellum). These inputs
modulate the output of M1 by providing information about the positioning, timing, and
coordination of voluntary movements. The output of M1 goes by way of the internal
capsule to synapse in the brainstem (the projection referred to as the corticobulbar tract)
or the spinal cord (the corticospinal tract). Damage to M1 will cause contralatereral
motor deficits, initially a flaccid hemiplegia/hemiparesis and later a spastic
hemiplegia/hemiparesis. Depending on the extent of cortical damage, these deficits
may be localized to a specific region of the body or can be more widespread.
2. Premotor Cortex (BA6): The premotor cortex is located immediately rostral to M1.
Its primary function is to assist in integration of sensory and motor information for the
performance of an action (praxis). Thus it receives input from secondary
somatosensory area (immediately caudal to S1 in the parietal cortex) and the ventral
anterior thalamic nucleus (a relay nucleus with projections from the basal ganglia,
which themselves are a group of subcortical nuclei that modulate motor activity). The
output of premotor cortex is to M1 and contralateral premotor area (by way of the
corpus callosum). Damage to premotor cortex may result in (1) apraxia, an acuired
inability to carry out skilled actions that could previously be performed (but without
paralysis); (2) deficits in contralateral fine motor control, such as the performance of
complex serial movements; and (3) difficulty in using sensory feedback for the control
and performance of movements.
3. Frontal eye fields (BA8): The frontal eye fields are located rostral to premotor cortex.
Their primary function is associated with control of voluntary eye movements in the
contralateral visual field for processes such as active visual search. Their connections
