Physiological correlates of intelligence

An interim report is presented illustrating differences in physiological response to atropine among mental defectives of low and high-grade intelligence. Epileptics, and patients with evidence of organic brain lesions, were excluded from the series. Certain types of response common in schizophrenics occur more frequently among the low-grade defectives, and show increasing intensity over the period of adolescence, while the converse is true of high-grade groups. A concept of ‘inadequate improvement on pre-existing schizophrenic tendencies’ is postulated as a factor in determining the degree of intellectual deficiency in mental defectives of this series. A speculative attempt is made to reconcile this finding with our current knowledge of mental growth in childhood, and is advanced as a possible line of thought for further research.