Blinking and schizotypal thinking.
Spontaneous eye blink rate (SBR) is thought to be a biological marker for cerebral dopamine (DA) activity. Accordingly, positive psychotic symptoms have been found to be associated with an increased SBR and negative psychotic symptoms with a decreased SBR. However, modulations of the DA system in patient populations also result from prior neuroleptic treatment. Here, we tested the possible relationship between SBR and positive and negative schizotypal thought. To test the direct influence of DA on SBR in general and as a function of schizotypy, half of a sample of 40 healthy men received levodopa and the other half placebo in a double-blind procedure. SBR did not differ between substance groups suggesting that a pharmacologically induced DA increase in healthy individuals does not generally increase SBR. However, in the levodopa group, increasing SBR correlated with increasing negative schizotypy scores, while no relationship was found between SBR and (1) negative schizotypy in the placebo group, or (2) positive schizotypy in either substance group. We conjecture that a pre-existing hypodopaminergic state in high negative schizotypy scorers, made these individuals susceptible to an increased DA concentration, as it has been observed in Parkinson's disease. Furthermore, the absence of any relationship in the placebo group might suggest that variations in DA concentration as a function of schizotypy are too subtle to influence SBR. Finally, the lack of any association of SBR with positive schizotypy might indicate that SBR and positive schizotypy are mediated by functionally distinct neural circuits.