Memory Loss & the Brain

In most kinds of dementia, autopsy reveals widespread degeneration in the cerebral cortex - such as the plaques and tangles which are the hallmark of Alzheimer's disease. Alzheimer's disease and frontotemporal dementia are therefore sometimes classed as "cortical dementias." In other kinds of dementia, there is targeted damage to regions lying under the cortex, giving rise to the category known as "subcortical dementias". This terminology is somewhat misleading, because both classes of dementia can cause damage to both cortical and subcortical areas. However, it is roughly true that the earliest symptoms in "cortical" dementia include difficulty with high-level behaviors such as memory, language, problem-solving and reasoning; these functions tend to be less impaired in "subcortical" dementia. Subcortical dementia is more likely to affect attention, motivation and emotionality. People with subcortical dementia often show early symptoms of depression, clumsiness, irritability or apathy. As the disease progresses, though, memory and judgment problems arise, and the end stages of subcortical dementia result in the same total breakdown of brain function as in the cortical dementias.

Parkinson's Disease is a disease that is usually classed as a motor disorder; its most obvious symptoms include tremor, muscular weakness and rigidity. Currently, it is believed that these symptoms reflect cell loss in a small brain region known as the substantia nigra which provides a vital neurochemical, dopamine, to other brain areas. About 30% of patients with Parkinson's disease also develop subcortical dementia. This mental deterioration appears to be part of the normal progress of the disease. In addition, some individuals with Parkinson's disease appear to develop a kind cortical dementia similar to Alzheimer's disease. This occurs at a higher rate than would be expected in the general population. Thus, it may be that individuals with Parkinson's disease are coincidentally at higher risk for Alzheimer's disease, for reason or reasons unknown.

Huntington's Disease is another "motor" disease, in which patients develop involuntary dance-like movements. It is an inherited disease, which means that if a parent passes the appropriate gene to a child, that child will eventually develop the disease. Huntington's disease results from degeneration of a brain area known as the basal ganglia, which is important in generating voluntary movements. Early in the course of the disease, patients may also show emotional problems, typically fits of depression or irritability. Later in the disease, subcortical dementia occurs. (In some cases, though, memory loss is among the earliest of symptoms.) There is no cure and no good treatment; tranquilizers may be used to control the involuntary movements and alleviate depression, but they cannot reverse the disease nor stop mental deterioration.

HIV Dementia is caused by the HIV virus, the virus that causes AIDS. The HIV virus attacks and progressively destroying the immune system. The HIV virus can directly infect the brain and can also weaken the immune system, allowing other infections to enter the brain and cause encephalitis. The resulting brain damage may be visible on MRI as generalized brain atrophy (shrinkage) and also visibly damaged subcortical areas. The behavioral symptoms parallel dementia - indeed, the condition is often called the AIDS-dementia complex. Early symptoms include memory loss, loss of concentration, and personality changes. In later stages, there can be confusion and sometimes psychosis.