Damage and Disease
---Damage, disease or maldevelopment interfering with a specific region of the brain may impair the function that that part controls or helps to co-ordinate. Here, we show some examples of local damage and its effects on senses, bodily control, personality and intellect.
---Damage to specific association areas - areas making most of the cerebral cortex - produces strange phenomena collectively called agnosias, aphasias and apraxias.
---People with agnosia fail to notice or recognise certain kinds of familiar things around them. If damage involved the dominant hemisphere’s area number 40 (as plotted by brain cartographer Korbinian Brodmann) there will be astereognosis - inability to recognise by touch familiar objects like a coin or ball. Damage to area 22 on the same side of the brain produces auditory agnosia - failure to recognise familiar sounds including spoken words. If area 39 on the same side of the brain malfunctions, a person cannot recognise familiar objects that he sees.
---Aphasias are language disorders produced by damage to certain other regions of the dominant hemisphere. Injury to areas 22 and 39 produces sensory aphasia - inability to understand spoken or written words, through these are recognised. If some cannot use part f the back of the temperoparietal region he suffers motor aphasia - and cannot meaningfully express his thoughts in speech or writing.
---Individuals with apraxias have intact nerve pathways between brain and muscles, yet cannot purposefully carry out skilled, complicated movements. Apraxias include agraphia, inability to write or draw; oral dysphasia, inability to speak articulately; and transmissive apraxia, inability to wash face, brush teeth, comb hair, or perform similar sequence of tasks to order, while remaining able to complete these acts unthinkingly. Brain regions involved include areas 44 and 45 (oral aphasia), area 40 alias the supramarginal gyrus (transmissive aphasia), other cortex regions, and connecting fibres.
---Hippocampus damage may interfere with memory. Prefrontal lobe damage can cause personality disorders.
---Deep inside the brain, lesions cause other problems. Thus damage at different points along the visual pathways produces various visual field defects. Failure of the hypothalamus to form the anti-diuretic vasopressin (ADH) can cause diabetes insipidus. Certain forms of damage to the thalamus make someone supersensitive to heat, cold, pain and pressure.
---Because nerve tracts from brain to spinal cord cross over in the brainstem, damage to one cerebral hemisphere may paralyse the other side of the body. However, damage to one side of the cerebellum affects body movements on that side. Cerebellar lesions may cause the puppetlike jerky movements of asynergia and dysmetria ("past-pointing" - pointing to one side of the object and overshooting); intention tremor; ataxia (walking with a broad-based, "drunken" gait); and dysarthria (speaking in a slurred, staccato fashion). Damage to both cerebellar hemispheres most affects the hands; damage to the middle of the cerebellum so afflicts the trunk that walking and even sitting upright may be impossible. Brainstem damage has different effects depending on which section (midbrain, pons or medulla) is affected, and which segment at that level in involved. For example, one-sided damage to part of the midbrain roof may produce so-called intention tremor and unsteady, broad based gait. Damage to the basal and medial region of the pons produced double vision and partial paralysis of both sides of the body. Damage to one side of the medulla may make swallowing difficult, banish gag reflex on the same side, and remove pain and temperature sensation from the same side of the face, the opposite side of the body, and the back of the head. In each case, of course, damage done depends on the nerve pathways involved. In mentally retarded individuals, brain damage often seems widespread. Examining a brain after death may show that the whole organ has shrunk or never fully grown. Sometimes the glial ("glue") cells of the white matted may have spread at the expense of the neurons in the grey matter. Sometimes the white matter itself seems wasted. But there can be local trouble, too, as in the maldevelopment of the cerebellum or the frontal lobes, or local haemorrhage, injury, or infection.
---So far, researchers have failed to find lesions in the brain to explain such lesser mental problems as dyslexia, or reading difficulty, a disability also affecting spelling. Dyscalculia, calculating difficulty, is another well-known learning problem. About 15 per cent of American school-age children reportedly suffer some learning difficulty or another. Many find that special tuition techniques prove helpful. The following sites explore the specific types of injury and ailment that afflicts the brain and what medicine does to minimise their ill-effects.