D-amphetamine depresses visual responses in the rat superior colliculus: a possible mechanism for amphetamine-induced decreases in distractibility.

Amphetamines can enhance sustained attention, and reduce distractibility, in normal subjects and patients with attentional-deficit/hyperactivity disorder (ADHD). Their mechanism of action in this regard is unknown, however one possibility is that the drugs affect the superior colliculus (SC), a structure with a clearly defined role in distractibility. The aim of the present studies was to explore the effect of systemically and locally administered d-amphetamine on visual responses in the superficial layers of the SC to wholefield light flashes in the rat, using local field potential and multi-unit recording. Systemic and intra-collicular d-amphetamine both produced a dose-related depression of visual activity, which sometimes progressed to inactivation of the multi-unit response at the highest dose. As a consequence, it is possible that amphetamines enhance sustained attention, and reduce distractibility, via an action on the colliculus. A corollary of this is that collicular dysfunction may underlie enhanced distractibility in ADHD.