The common subjective experience after consuming cannabis is that sounds seem noticeably louder, sharper, or more distracting than usual. This phenomenon, often described as “heightened hearing,” suggests a temporary change in how the brain processes acoustic information. Sounds typically ignored, such as the distant hum of a refrigerator or the subtle texture of a familiar song, become acutely salient and demanding of attention. Neuroscientists seek to understand why the psychoactive compound delta-9-tetrahydrocannabinol (THC) causes this shift in auditory awareness.
Sensory Input Versus Auditory Perception
The feeling of “heightened hearing” is not due to a physical change in the ear itself; the mechanical function of the eardrum or the cochlea is not enhanced. Auditory input—the physical sound wave energy that enters the ear—remains essentially the same after cannabis consumption. The perceived intensity change occurs much further along the pathway, in the central nervous system.
The distinction lies between sensory input and auditory perception, which is the brain’s interpretation of that input. The actual physical acuity, or the ability to detect fainter sounds, is generally not improved by THC. Instead, the compound alters the neural processing of existing sound signals, making them feel more salient or intense as they travel toward conscious awareness. This modification of how the brain weights acoustic information leads to the subjective experience of sounds being louder or sharper.
The Endocannabinoid System and Auditory Pathways
The mechanism behind this altered perception begins with the endocannabinoid system (ECS), the body’s network of receptors and signaling molecules that regulate numerous functions, including sensory processing. THC, the primary psychoactive component of cannabis, acts by binding to and activating Cannabinoid Receptor Type 1 (CB1R). These receptors are densely distributed in brain regions responsible for relaying and interpreting sound.
CB1 receptors are found throughout the auditory pathway, including the inferior colliculus (IC), the auditory thalamus, and the primary auditory cortex (AC). The inferior colliculus, located in the midbrain, is a major relay center where sound information converges before moving to the thalamus. The binding of THC to CB1 receptors in these regions modulates the release of neurotransmitters, fundamentally changing the fidelity and strength of the sound signals passed along the circuit.
In the primary auditory cortex, where sound is consciously interpreted, CB1R activation can disrupt the normal balance of excitatory and inhibitory signals. THC often inhibits the release of various neurotransmitters, affecting the precise timing and amplitude of the neural response to sound. This modulation alters how sound waves are encoded into electrical signals, changing the perceived characteristics of the sound. This disruption sets the stage for the functional change in how the brain manages acoustic attention.
Altered Sound Filtering and Attention Gating
The functional outcome of THC’s action in the auditory pathway is the impairment of sensory gating, or auditory filtering. Sensory gating is the brain’s ability to automatically suppress repetitive, irrelevant background stimuli, allowing cognitive resources to focus on important or novel information. For example, the brain normally gates out the constant noise of a fan or the distant sound of traffic.
Scientific studies, often using a measure called P50 suppression, show that acute THC consumption disrupts this filtering mechanism. The P50 component is an early electrical response in the brain to an auditory stimulus. Healthy brains typically show a reduced P50 response to a second, identical sound presented milliseconds after the first, indicating successful gating. THC use impairs this suppression, meaning the brain registers the second, repetitive sound with nearly the same intensity as the first.
When this auditory filter fails, all acoustic stimuli, regardless of their importance or novelty, flood conscious perception equally. The background hum of the refrigerator or the subtle details of a song become acutely salient and distracting because the brain is unable to categorize them as “irrelevant.” This failure to filter is the primary reason sounds feel overwhelming, louder, or sharper when under the influence of cannabis.