The ventral premotor cortex, or vPMC, is an area of the brain’s frontal lobe that has a multifaceted role in action. It is involved in the planning and sensory guidance of movement, as well as in understanding the actions of others. The vPMC is not a single, uniform structure; rather, it has different subregions with distinct properties and functions. This brain region contributes to behavior by sending signals to the spinal cord, with a particular emphasis on the trunk muscles of the body.
Anatomical Overview of the Ventral Premotor Cortex
The premotor cortex is situated in the frontal lobe of the brain, directly in front of the primary motor cortex. It is part of Brodmann area 6, a region of the cerebral cortex defined by its cellular structure. The vPMC is intricately connected to other parts of the brain, acting as a “project manager” that coordinates movement. It receives significant input from sensory areas, such as the parietal lobe, which processes information about touch and the spatial orientation of the body.
This connectivity allows the vPMC to integrate sensory information, which is important for guiding movements. For example, the vPMC has strong connections with the second somatosensory area and the anterior insular cortex, which are important for visuomotor coordination. The vPMC also sends signals to the primary motor cortex, which is responsible for the final execution of voluntary movements.
Guiding Action Through Sensory-Motor Integration
The process known as sensory-motor integration allows us to interact with our environment in a purposeful way. When you reach for a coffee mug, for instance, your brain takes in visual information about the mug’s size, shape, and location. This sensory data is then relayed to the vPMC.
The vPMC then selects the appropriate motor program to grasp the mug. This involves shaping the hand to fit the handle, determining the right amount of force to apply, and planning the trajectory of the arm. The vPMC is particularly important for guiding movements in response to nearby objects and maintaining a “safety margin” around the body.
Electrical stimulation of the vPMC in monkeys has been shown to elicit defensive movements, as if protecting the body from a perceived threat. This suggests that the vPMC is not only involved in planning actions but also in reacting to the immediate environment. The vPMC’s role in sensory-motor integration is therefore not limited to simple grasping movements but extends to more complex behaviors that require constant adjustment based on sensory feedback.
The Mirror Neuron System and Understanding Actions
One of the discoveries related to the vPMC is the mirror neuron system. These specialized neurons were first identified in the F5 area of the macaque monkey brain by a team of researchers led by Giacomo Rizzolatti. Mirror neurons have the unique property of firing both when an individual performs a specific action and when they observe another individual performing the same action. For example, a mirror neuron might fire when a monkey grasps a peanut, and also when it sees a person grasp a peanut.
This discovery has implications for our understanding of social cognition. The mirror neuron system is thought to be the basis for our ability to understand the actions and intentions of others. By internally simulating the actions of others, we can infer their goals. For instance, observing someone pick up a cup can trigger the same neurons that would fire if we were picking up the cup ourselves, allowing us to understand whether the person intends to drink from it or simply move it.
The mirror neuron system is not limited to visual observation. Some mirror neurons also respond to the sound of an action, such as the crack of a peanut shell. In humans, functional magnetic resonance imaging (fMRI) studies have shown that observing actions performed with different parts of the body, such as the hand, mouth, or foot, activates different sectors of the vPMC in a somatotopic pattern. This suggests that the mirror neuron system is highly organized and plays a role in a wide range of social interactions, including empathy and learning through imitation.
Connections to Speech and Language
The ventral premotor cortex also has a role in communication, particularly in the production of speech. It is located near Broca’s area, a region in the frontal lobe that is well-known for its role in language. The motor-related part of Broca’s area is primarily located in Brodmann area 44, which is considered to be the human homolog of the monkey area F5 where mirror neurons were first discovered.
The vPMC is involved in the fine motor control of the orofacial muscles, which include the lips, tongue, and larynx. This control is necessary for the physical production of speech sounds. The vPMC is part of a dorsal stream of speech processing that maps sensory speech representations to articulatory motor cortices. This stream is thought to involve a sensorimotor interface that translates auditory speech signals into motor representations.
The connection between the vPMC and speech has led to the theory that human language may have evolved from a system of hand and mouth gestures. Some researchers have proposed that the vPMC contains a “mental syllabary,” which is a repository of gestural scores for the most frequently used syllables in a language.