FoundationalConceptsNeuroscience

partial paralysis. For example, a lesion from a stroke that produced
significant damage to the right posterior frontal lobe would result in
paralysis of the left side of the body.
Anterior to M1 in the frontal lobes are several other areas also
intimately involved in the control of body movement. These areas are
collectively called the supplementary motor areas, or premotor areas.
Neurons in these areas are active before the generation of signals in
M1 and are involved in planning and sequencing muscle movements.
Lesions in the premotor areas do not result in paralysis but give rise to
disorganizations of movement. Suppose we consider a complex motor
action such as picking up a key, inserting it into a lock, and turning the
key to open the lock. A person with a frontal premotor lesion might
still be able to execute all the individual movements associated with
the particular action but would not be able to organize and sequence
them appropriately. Such disorders in the organization of movement
are called apraxias. These are to movement as agnosias are to sensory
perception—disorders of organization.
Functional and structural studies of the brain have revealed a vast
interconnectivity between diverse regions of the cerebral cortex. For
example, large numbers of axons interconnect (in both directions) the
posterior sensory areas serving vision, audition, and touch with an-
terior motor regions. It is believed that, when efferent motor signals
are sent from M1 to the peripheral muscles to trigger movement, an
“efference copy” is also conveyed to sensory cortex, so that the brain
immediately “knows” what the body is doing and can plan accord-
ingly. Constant communication between sensation and movement
makes eminent sense, because to execute smooth movement through
the environment, movement must be continuously integrated with
knowledge about one’s surroundings obtained via sensory perception.
A manifestation of this sensory-motor interconnectivity are neu-