FoundationalConceptsNeuroscience

Amnesia may be associated with various kinds of physical injury
to the brain: cellular damage from stroke or seizure, brain tumor,
infection (encephalitis), or traumatic injury sustained in an accident.
Surgical excision of brain tissue can result in amnesia. Electrocon-
vulsive shock therapy (ECT)—a psychiatric procedure in which
seizures are induced in a patient, with the goal of reducing symptoms
of depressed mood—generally produces retrograde amnesia. This is
believed to result from the disruptive action of ECT on memory con-
solidation, so that more recent, less consolidated, memories are lost.
(The mechanism by which ECT affects mood is unknown.)
Memory pathology is also a hallmark symptom of dementia, a
neurological condition characterized by global loss of cognitive
abilities—not only memory but other capacities, such as attention,
judgment, planning, problem solving, and motor coordination. Mem-
ory problems in dementia generally begin with anterograde effects—
the inability to retain new information. If the dementia is sufficiently
severe, retrograde memory loss may eventually also develop. Severe
dementia is a deteriorating condition that can result in seriously dis-
organized behavior, including even the apparent loss of sense of self,
the knowledge of who one is.
Two common forms of dementia are vascular and Alzheimer’s.
Vascular dementia is associated with the accumulation of cellular
damage in the brain related to impaired blood circulation—generally
due to atherosclerosis or repeated small strokes. Alzheimer’s dementia
is associated with the presence in the brain of what are called senile
plaques (extracellular deposits of aggregates of a polypeptide called
beta amyloid) and neurofibrillary tangles (aggregates of tau protein,
a protein involved in the assembly and stabilization of microtubules).
However, the ultimate causes of this condition and how to prevent its
onset are not presently understood.