Final answer:
Alcohol's most significant effect in the brain is enhancing the inhibitory effects of the neurotransmitter gamma-Aminobutyric acid (GABA) by acting as a GABA agonist, which leads to hyperpolarization of neurons and a general calming of brain activity.
Step-by-step explanation:
The most important effect of alcohol in the brain is believed to be enhancing gamma-Aminobutyric acid's (GABA's) inhibitory effects. GABA is the main inhibitory neurotransmitter in the central nervous system (CNS), which means it plays a critical role in calming neural activity. Ethanol (alcohol), along with other psychoactive drugs like barbiturates and benzodiazepines, are GABA agonists and work by promoting the activity of GABA receptors in the brain.
When alcohol binds to these receptors, it facilitates the opening of the GABA-gated chloride channels, allowing negatively-charged chloride ions into the neuron. This influx of chloride ions hyperpolarizes the neuron, pushing it further away from firing. Thus, activating a GABA neuron has a quieting effect on the brain. This action of alcohol results in effects that can range from social disinhibition to severe impairment of motor control and decision-making, and in cases of excessive consumption, to sedation or even death.
Chronic alcohol exposure can lead to compensatory adaptations in the brain's reward circuitry, which may result in the development of tolerance, meaning that higher doses of alcohol are needed to achieve the same effects, and withdrawal symptoms when consumption is stopped.