MIDLATENCY AUDITORY EVOKED-RESPONSES - P1 ABNORMALITIES IN ADULT AUTISTIC SUBJECTS

MLR recordings from a group of 11 high-functioning adult autistic subj ects were compared with those from a control group of 11 normal subjec ts. Components selected for analysis were "Pa," the maximum positivity in the 25-40 msec latency range following stimulus onset, "P1," the m aximum positivity within the 50-65 msec latency range, and "Nb," the m aximum negative deflection in the 40-50 msec latency range. Statistica l analyses of amplitude and latency data were conducted using repeated measures analysis of variance and t test group comparisons. The Pa co mponent showed no significant difference between autistic and control groups. However, 2 types of abnormality were noted in the P1 component : (1) the P1 component was significantly smaller in the autistic subje cts at slow rates of stimulation, and (2) the autistic P1 did not chan ge as rates of click stimulation increased from 0.5 to 10/sec, in cont rast to the normally produced P1 decrement. Data from the P1 model in the cat, and complementary data from the human, closely link the gener ator substrate of the P1 potential to cholinergic components of the as cending reticular activating system (RAS) and their thalamic target ce lls. This is the first report of abnormal P1 responses in autism and s trongly suggests that the RAS and/or its post-synaptic thalamic target s may be dysfunctional in this syndrome.