Page 23 - Handbook of Electronic Assistive Technology

10 HANDBOOK OF ELECTRONIC ASSISTIVE TECHNOLOGY

Hemisphere dominance and handedness are not always the same. The left hemisphere
is used for comprehension and control of speech in 98% of adults, whereas only 90% of us
are right handed.
There are specific areas of the brain that are vital for the processing and expression of
language. Broca’s area is involved in creating speech and is situated at the side of the tem-
poral lobe just in front of the motor cortex. Problems with this area, especially in the domi-
nant left hemisphere, can lead to transient or even permanent loss of speech together with
a right hemiplegia. Wernicke’s area at the back of the temporal lobe is not so near to the
motor cortex. Damage to this leads to a problem with language content. Individuals with
a problem in this area can speak with normal grammar, syntax, rate, intonation and stress,
but they may use the wrong words, insert nonexistent words, or string normal words
together randomly. They do retain the ability to sing or to recite something memorised.
Toward the centre of each cerebral hemisphere are fluid-filled spaces called ventricles –
third, fourth and lateral. As we’ve discussed, many of the long tracts that transmit neu-
ronal messages from the cortex to the brain stem and beyond are situated close to these
lateral ventricles in the white matter periventricular area.
As stated, each hemisphere interacts primarily with the opposite side of the body, with
motor messages crossing at the brain stem level. Each side also interacts with the other
hemisphere by a large bundle of nerve fibres called the corpus callosum, which connects
the mirror image points.
The brain stem is a hugely complicated network of both groups of cells, such as neu-
ronal grey matter basal ganglia (e.g., putamen, globus pallidus and thalamus), and also
nerve fibre/white matter pathways, all massively interlinked like a complex internet sys-
tem. Most of our automatic feelings, emotions and movements rely on the integrity of
these areas.
The major sensory inputs from our skin, in terms of touch, pain, hot and cold, are also
relayed through the thalamus of the brain stem to the parietal lobe for processing.

Motor System
We all know by watching squirming babies that early patterns of movement are similar
in almost everybody. We sit before we crawl, then stand and then walk. These functional
abilities are synchronised by patterns created by the physical and physiological develop-
ment of the nervous system.
Even in the womb, our spinal cord level reflexes stimulate and co-ordinate uncon-
scious, simple rhythmic movements in muscle groups. When we are born, these primi-
tive reflexes are involved with important functions: rooting for the nipple, sucking and
swallowing. As we grow, our brains develop similar reflex motor unit patterns in our
limbs and trunk with ever-increasing complexity of balanced muscle stimulation and
relaxation.
These rhythmic motor patterns at the spinal level, called central pattern generators,
have to be started, directed, sped up and slowed down. We do this by using the CNS to