Alcohol is a central nervous system depressant. When consumed, it is quickly absorbed into the bloodstream and travels to the brain, where its effects are not uniform across all regions. Brain functions are progressively impaired as the concentration of alcohol in the blood, known as the Blood Alcohol Content (BAC), rises. The sequence of effects begins with regions responsible for higher-order thinking and moves toward areas that control basic survival functions.
The Initial Target: Prefrontal Cortex
The first area of the brain significantly impacted by alcohol is the prefrontal cortex, which is part of the cerebral cortex. This region is responsible for executive functions, including complex planning, personality expression, regulating social behavior, and making decisions. Since it governs advanced cognitive abilities, interference here results in the earliest noticeable changes in behavior.
Impairment of the prefrontal cortex leads to a reduction in inhibitory control, often resulting in increased talkativeness or a false sense of confidence. Decision-making becomes slower and less rational because the ability to weigh consequences is diminished. This explains why a person might engage in riskier behavior or have reduced self-control before motor skills are obviously affected.
Deepening Intoxication: The Limbic System and Cerebellum
The Limbic System
As the BAC continues to climb, alcohol affects deeper structures, including the limbic system, which regulates memory and emotion. The hippocampus, essential for forming new memories, is impaired within this system. This interference can lead to exaggerated mood swings and emotional responses. Disruption of the hippocampus also causes memory impairment, including the temporary inability to recall events that occurred while drinking (a blackout).
The Cerebellum
Simultaneously, the cerebellum, located at the back and base of the brain, begins to malfunction. This structure is responsible for coordinating voluntary movements, balance, and posture. Its impairment results in the characteristic physical signs of intoxication. These signs include slurred speech, an unsteady gait, and a loss of fine motor control.
The Mechanism of Action: Neurochemical Changes
Alcohol acts by altering the balance between the brain’s primary inhibitory and excitatory systems using chemical messengers, or neurotransmitters. The main inhibitory neurotransmitter, Gamma-aminobutyric acid (GABA), is enhanced by alcohol. When alcohol binds to GABA-A receptors, it intensifies GABA’s natural calming effect, essentially putting a brake on neural activity. This increased inhibition contributes to feelings of relaxation, sedation, and the overall slowing of brain function.
At the same time, alcohol suppresses the activity of glutamate, the brain’s primary excitatory neurotransmitter. Glutamate is responsible for increasing brain activity, contributing to alertness and quick reaction times. The combined effect of enhancing the inhibitory system and suppressing the excitatory system causes the cognitive and motor impairment observed during intoxication.
Severe Intoxication: Impact on the Brainstem
The final and most dangerous stage of alcohol intoxication involves the brainstem, which connects the cerebrum and cerebellum to the spinal cord. The brainstem is responsible for regulating involuntary, life-sustaining functions, such as breathing, heart rate, and body temperature. As the BAC reaches dangerously high levels, the depressant effect of alcohol overwhelms the brainstem, causing these vital functions to slow down or fail. This severe depression can lead to stupor, coma, respiratory failure, and death, signaling a life-threatening emergency.