SENSORY INATTENTION PRODUCED BY 6-HYDROXYDOPAMINE-INDUCED DEGENERATION OF ASCENDING DOPAMINE NEURONS IN BRAIN

Unilateral 6-hydroxydopamine-induced degeneration of ascending dopamine neurons caused a pronounced deficiency in the ability of rats to orient toward sensory stimuli presented on the contralateral side of the body. The behavior of the animals went through 3 phases. The first 2 days after the operation the animals showed great individual variations with hypo- as well as hyperreactivity on the contralateral side. This phase coincided with the degeneration of the dopamine neurons. The 2nd phase lasted from the 3rd to the 5th day and was characterized by contralateral inattention to olfactory, tactile, auditory and visual stimuli. The 3rd phase started on day 6 and was characterized by gradual recovery in the reaction to sensory stimuli. The fact that an animal was able to respond to olfactory, auditory and visual stimuli at a time when it was not able to orient toward a tactile stimulus shows that the deficiency was not due to a motor impairment. The animals never regained their ability to orient toward tactile stimuli. The findings provide strong evidence that the syndrome of sensory inattention was due to a degeneration of ascending dopamine neurons, most probably the nigrostriatal pathway. The syndrome may be a disruption of sensory motor integration.