Williams' autopsy revealed that he had been suffering from an extreme case of Lewy body dementia, which had been misdiagnosed as Parkinson's disease.

Dementia with Lewy bodies (DLB) is a type of dementia that worsens over time. Additional symptoms may include fluctuations in alertness, visual hallucinations, slowness of movement, trouble walking, and rigidity. Excessive movement during sleep and mood changes such as depression are also common. The underlying mechanism involves the buildup of Lewy bodies, clumps of alpha-synuclein protein in neurons. DLB is the most common cause of dementia after Alzheimer's disease and vascular dementia.

Alpha-synuclein, encoded by the SNCA gene, is predominantly expressed in the neocortex, hippocampus, substantia nigra, thalamus, and cerebellum. Alpha-synuclein is specifically upregulated in a discrete population of presynaptic terminals of the brain during a period of acquisition-related synaptic rearrangement. Apparently, alpha-synuclein is essential for the normal development of cognitive functions. Knock-out mice with the targeted inactivation of the expression of alpha-synuclein show impaired spatial learning and working memory.

Studies suggest a role for alpha-synuclein in maintaining a supply of synaptic vesicles in presynaptic terminals by clustering synaptic vesicles. It may also help regulate the release of dopamine, a critical neurotransmitter for controlling the start and stop of voluntary and involuntary movements.

Note that the neurological Reward System utilizes the mesolimbic dopamine pathway as an important part of its function. The Reward System is responsible for incentive salience (i.e., motivation and "wanting", desire, craving), associative learning (primarily positive reinforcement and classical conditioning), and positive emotions, particularly pleasure (e.g., joy, euphoria and ecstasy). The amygdala is involved, which perform a primary role in the processing of memory, decision-making, and emotional reactions. The amygdalae are considered part of the limbic system.

In pathological conditions, alpha-synuclein aggregates to form insoluble fibrils characterized by Lewy bodies, such as in Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. These disorders are known as synucleinopathies. Alpha-synuclein is the primary structural component of Lewy body fibrils.

Robin Williams' wife, Susan, wrote the following description of what Williams' had experienced during the year before he died: "The terrorist inside my husband's brain".

Important → This essay may offer insights into the various cognitive areas of perception and response that are related to development, maintenance, and persistence of humor, amusement, and fun. The brain is extraordinarily complex, and within its physiology, structures, and chemistries lie the various Personality Filter subroutines that could be explored scientifically for Humor by those moved to do so. ← Important