APA Dictionary of Psychology

a rapidly progressive adult-onset disease involving degeneration of both lower motor neurons, responsible for muscle contraction, and upper motor neurons, responsible for muscle spindle sensitivity, and leading to death within 5 years of diagnosis. Symptoms include muscular atrophy and weakness, partial and complete paralysis, speech impairment, and difficulties swallowing or breathing. Amyotrophic lateral sclerosis is often used interchangeably with motor neuron disease, especially in the United States. Also called Lou Gehrig’s disease.