Premotor cortex
Introduction
The premotor cortex is a region of the frontal lobe of the brain, situated anterior to the primary motor cortex. It plays a crucial role in the planning and execution of movements. This area is involved in the coordination of complex movements and is essential for motor control. The premotor cortex integrates sensory information and uses it to guide motor actions. It is divided into several subregions, each with distinct functions and connections.
Anatomy and Structure
The premotor cortex is located in the frontal lobe, just anterior to the primary motor cortex (Brodmann area 4). It is part of Brodmann area 6, which also includes the supplementary motor area (SMA). The premotor cortex can be further subdivided into the dorsal premotor cortex (PMd) and the ventral premotor cortex (PMv).
Dorsal Premotor Cortex (PMd)
The PMd is situated in the superior part of the premotor cortex. It is involved in the planning of movements, particularly those that require spatial and sensory guidance. The PMd receives input from the parietal cortex, which provides information about the spatial location of objects and the body's position in space.
Ventral Premotor Cortex (PMv)
The PMv is located in the inferior part of the premotor cortex. It plays a role in the control of hand and mouth movements, as well as in the recognition of actions performed by others. The PMv is connected to the inferior parietal lobule and the inferior frontal gyrus, which are involved in the processing of sensory information and language, respectively.
Functions
The premotor cortex is involved in various aspects of motor control, including the planning, selection, and initiation of movements. It integrates sensory information to guide motor actions and is essential for the coordination of complex movements.
Motor Planning
One of the primary functions of the premotor cortex is motor planning. This involves the selection and sequencing of movements based on sensory input and internal goals. The premotor cortex works closely with the primary motor cortex to execute these planned movements.
Sensory-Motor Integration
The premotor cortex integrates sensory information from various sources, including the parietal cortex and the thalamus. This sensory information is used to guide motor actions, ensuring that movements are accurate and appropriate for the current context.
Action Recognition
The ventral premotor cortex (PMv) is involved in the recognition of actions performed by others. This function is thought to be related to the mirror neuron system, which allows individuals to understand and imitate the actions of others.
Connectivity
The premotor cortex has extensive connections with other regions of the brain, including the primary motor cortex, the parietal cortex, the thalamus, and the basal ganglia. These connections are essential for the integration of sensory information and the coordination of motor actions.
Cortical Connections
The premotor cortex is connected to various cortical regions, including the primary motor cortex, the parietal cortex, and the prefrontal cortex. These connections allow the premotor cortex to integrate sensory information and plan movements based on internal goals and external stimuli.
Subcortical Connections
The premotor cortex also has connections with subcortical structures, including the thalamus and the basal ganglia. These connections are important for the modulation of motor activity and the coordination of complex movements.
Clinical Significance
Damage to the premotor cortex can result in various motor deficits, including apraxia, which is characterized by the inability to perform purposeful movements despite having the physical ability to do so. Lesions in the premotor cortex can also affect the ability to plan and execute movements, leading to difficulties in performing everyday tasks.
Apraxia
Apraxia is a motor disorder that results from damage to the premotor cortex or its connections. Individuals with apraxia have difficulty performing purposeful movements, even though they have the physical ability to do so. This condition can affect various types of movements, including those involving the hands, mouth, and limbs.
Motor Planning Deficits
Damage to the premotor cortex can also result in deficits in motor planning. This can lead to difficulties in initiating and sequencing movements, making it challenging to perform complex tasks that require precise coordination.
Research and Future Directions
Ongoing research is focused on understanding the specific functions of the different subregions of the premotor cortex and their roles in motor control. Advances in neuroimaging techniques, such as functional MRI and diffusion tensor imaging, are providing new insights into the connectivity and function of the premotor cortex. Future research may lead to new treatments for motor disorders resulting from damage to this region.