occurs when the exposure to natural or artificial toxic substances, which are called neurotoxins
, alters the normal activity of the nervous system
in such a way as to cause damage to nervous tissue. This can eventually disrupt or even kill neurons
, key cells that transmit and process signals in the brain and other parts of the nervous system. Neurotoxicity can result from exposure to substances used in chemotherapy
, radiation treatment
, drug therapies
, certain drug abuse, and organ transplants
, as well as exposure to heavy metals
such as lead
, certain foods
and food additives
, industrial and/or cleaning solvents
, and some naturally occurring substances. Symptoms may appear immediately after exposure or be delayed. They may include limb weakness or numbness, loss of memory, vision, and/or intellect, headache, cognitive and behavioral problems and sexual dysfunction. Individuals with certain disorders may be especially vulnerable to neurotoxins.
The name implies the role of a neurotoxin although the term 'neurotoxic' may be used more loosely to describe states that are known to cause physical brain damage but where no obvious neurotoxin has been identified.
The term neurotoxic is used to describe a substance, condition or state that damages the nervous system and/or brain, usually by killing neurons. The term is generally used to describe a condition or substance that has been shown to result in observable physical damage. The presence of neurocognitive deficits alone is not usually considered sufficient evidence of neurotoxicity, as many substances exist which may impair neurocognitive performance without resulting in the death of neurons. This may be due to the direct action of the substance, with the impairment and neurocognitive deficits being temporary, and resolving when the substance is metabolised from the body. In some cases the level or exposure-time may be critical, with some substances only becoming neurotoxic in certain doses or time periods.
The prognosis depends upon the length and degree of exposure and the severity of neurological injury. In some instances, exposure to neurotoxins can be fatal. In others, patients may survive but not fully recover. In other situations, many individuals recover completely after treatment.