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- Serotonin (5-hydroxytryptamine) is a monoamine neurotransmitter that plays a role in mood, eating, sleeping, arousal and potentially visual orientation processing. To investigate its function in visual orientation, researchers have utilised MDMA, or as it is commonly referred to, Ecstasy (3,4-methylenedioxymethamphetamine). MDMA is known to affect serotonin neurons in the brain and cause neurotoxicity. Serotonin has been hypothesised to be involved in visual orientation because individuals who use MDMA exhibit an increase in the magnitude of the tilt aftereffect (TAE). The TAE is a visual illusion where viewing lines in one direction, for an extended period of time, produces the perception of a tilt in the opposite direction to vertical lines subsequently viewed. This effect is proposed to occur due to lateral inhibition to orientation sensitive neurons in the occipital lobe. Lateral inhibition is where neurons that become activated to a particular orientation send inhibitory signals to their neighbouring neurons. The degree of orientation that each neuron becomes maximally excited to is referred to as the tuning bandwidth. Lateral inhibition consequently plays a pivotal role in each neuron's tuning bandwidth, such that if lateral inhibition no longer occurs, a greater number of neurons will become stimulated to the same orientation. This results in the activated neurons becoming adapted to the same orientation stimulus, if the stimulus is viewed for a period of time. As a consequence, if those neurons are subsequently 'shown' another stimulus that differs slightly in its orientation, those neurons are no longer able to achieve the same level of response as compared to other non-adapted neurons. Studies have consequently utilised the TAE to assess the degree of lateral inhibition that occurs from MDMA use. The results of these studies have found evidence to support the role that serotonin plays in visual orientation. This was evidenced through individuals who solely used MDMA reporting a greater magnitude of the TAE compared to drug naive controls. This increased magnitude showed that serotonin plays a role in lateral inhibition by potentially having a honing effect, meaning that orientation neurons become maximally excited to their preferred orientation, and less so to others. This additionally provides further evidence of the neurotoxicity of MDMA. This area of research, overall, has provided insights into the mechanisms of visual orientation processing and the effect that MDMA neurotoxicity has on this system. This furthers the understanding of both the role that serotonin has on the visual system and to what degree MDMA neurotoxicity affects the brain. (en)
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- Serotonin (5-hydroxytryptamine) is a monoamine neurotransmitter that plays a role in mood, eating, sleeping, arousal and potentially visual orientation processing. To investigate its function in visual orientation, researchers have utilised MDMA, or as it is commonly referred to, Ecstasy (3,4-methylenedioxymethamphetamine). MDMA is known to affect serotonin neurons in the brain and cause neurotoxicity. Serotonin has been hypothesised to be involved in visual orientation because individuals who use MDMA exhibit an increase in the magnitude of the tilt aftereffect (TAE). The TAE is a visual illusion where viewing lines in one direction, for an extended period of time, produces the perception of a tilt in the opposite direction to vertical lines subsequently viewed. This effect is proposed to (en)
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- Role of serotonin in visual orientation processing (en)
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