Motor and Sensory Maps
The brain organizes motor output and sensory input using spatial maps. These are present to increase efficiency and enforce togetherness of related inputs and outputs. Maps also help during development as neuronal connections are formed.
It is likely a single point of input will activate a large population of neurons, meaning maps are fuzzy. A given sensory input will tend to activate an even larger group of neurons as the signal is disseminated during encoding and processing, with signal intensity will vary according to location.
Sensory Maps
Almost all sensory receptors, be they somatic sensory or visual, are laid out in planar sheets. Freqency maps and chemical maps are also generated by sensory signals.
Each sensory signal can be mapped many times within the brain, forming different, unique maps.
Homunculus
The homunculus is arranged, laterally to medially, with face, hand, arm, head, trunk, legs, then genitals. Relative size is determined by sensory fibre density.
Motor Maps
The primary motor map is arranged similarly to the sensory map, and there are many interconnections between the primary motor and somatosensory areas.
In some areas, motor and sensory functions can overlap each other precisely, such as occurs in the superior colliculus. The SC receives direct information from the retina and the visual cortex and can then cause head and eye movements to being the image into the centre of the fovea. The superior colliculus also has auditory and somatosensory maps, and together these inputs help orient to prominent stimuli.
Map Plasticity
Maps can change over time, with substantial reorganization of sensory and motor areas during development, behaviour, training, or damage.