Difference between revisions of "Transcranial Magnetic Stimulation and Brain Plasticity in Post-Stroke Recovery"

'''Multiple Motor Cortical Maps:''' Different body parts, such as the arm, leg, or face, have predominant representation in specific brain areas, but the representations of muscles of the same body part may overlap. In this respect, the motor cortex differs from the sensory cortex, which is organized in a simpler topography. For example, the cortical motor activity maps for the muscles that move different fingers are essentially the same, while in the sensory cortex, different fingers are represented separately, like the keys of a piano. Recent studies conducted at our center using TMS, stimulating the motor cortex and recording the motor response evoked from 12 muscles of the upper limb, have demonstrated that the neuron pools that govern various muscle groups have different excitability, accompanied by different scalp representation. Some muscles, in fact, showed a tendency to organize into “clusters,” aggregating into maps that widely overlapped each other, along with well-defined and separate hot-spot zones (point from which a motor response of minimum latency and maximum amplitude can be elicited) (Rossini and Pauri 2000, Fig.2).

The pioneering studies by Merzenich and collaborators, conducted on monkeys, demonstrated that the organization of the sensory cortex changes after the transient or permanent loss of sensory information from a part of the body (e.g., a limb). Similar observations have been made by Donoghue and collaborators on the motor cortex. These studies showed that the cortex, no longer connected to the periphery, does not remain inactive but is “invaded” by the representation of body parts adjacent to the deafferented area, which had, in other words, been deprived of sensory information. Following reversible deafferentation, there is a temporary rearrangement of the somatotopic organization of the fingers in the primary somatosensory cortex, consisting of the expansion or displacement of cortical areas activated by the stimulation of unanesthetized fingers at the expense of cortical neurons deprived of sensory feedback.