Hallucinogens.

Hallucinogens (psychedelics) powerfully alter perception, mood, and cognition, are physiologically safe, and do not cause dependence. Their use predates written history in ritual contexts. Early research linked LSD to serotonin (5-HT), and it is now known that hallucinogens stimulate 5-HT(2A) receptors on neocortical pyramidal cells, increasing cortical glutamate. These effects are compared to acute psychosis, with thalamocortical interactions key to altered states of consciousness. Brain imaging shows increased prefrontal cortical metabolism. The 5-HT(2A) receptor is essential for cognitive processing, and its ligands may aid cognitive neuroscience. Hallucinogens may also have therapeutic utility for alcoholism, substance abuse, and psychiatric disorders.

Study at a glance

Abstract

Hallucinogens (psychedelics) are psychoactive substances that powerfully alter perception, mood, and a host of cognitive processes. They are considered physiologically safe and do not produce dependence or addiction. Their origin predates written history, and they were employed by early cultures in a variety of sociocultural and ritual contexts. In the 1950s, after the virtually contemporaneous discovery of both serotonin (5-HT) and lysergic acid diethylamide (LSD-25), early brain research focused intensely on the possibility that LSD or other hallucinogens had a serotonergic basis of action and reinforced the idea that 5-HT was an important neurotransmitter in brain. These ideas were eventually proven, and today it is believed that hallucinogens stimulate 5-HT(2A) receptors, especially those expressed on neocortical pyramidal cells. Activation of 5-HT(2A) receptors also leads to increased cortical glutamate levels presumably by a presynaptic receptor-mediated release from thalamic afferents. These findings have led to comparisons of the effects of classical hallucinogens with certain aspects of acute psychosis and to a focus on thalamocortical interactions as key to understanding both the action of these substances and the neuroanatomical sites involved in altered states of consciousness (ASC). In vivo brain imaging in humans using [(18)F]fluorodeoxyglucose has shown that hallucinogens increase prefrontal cortical metabolism, and correlations have been developed between activity in specific brain areas and psychological elements of the ASC produced by hallucinogens. The 5-HT(2A) receptor clearly plays an essential role in cognitive processing, including working memory, and ligands for this receptor may be extremely useful tools for future cognitive neuroscience research. In addition, it appears entirely possible that utility may still emerge for the use of hallucinogens in treating alcoholism, substance abuse, and certain psychiatric disorders.