Event-related slow potential (ERSP) correlates of thyroid gland function level

This study shows an association between thyroid gland function level and event-related slow brain potential (ERSP) parameters (peak amplitude and area under the curve), obtained during "classical" and "operant" reaction-time paradigms. A significant positive correlation between ERSP parameters and 24-hr I131 uptake and a negative nonsignificant one between them and ankle jerk reflex were found. Organismic factors related to thyroid function had greater influence upon ERSP amplitude and area than situational ones, for no significant effect of task was evidenced and no interaction between them was found under the conditions employed. Hyper- and hypothyroids showed also a tendency to present longer reaction times than euthyroids. These results are discussed within the framework of the arousal-distraction coupling hypothesis as proposed by Tecce and Cole (1976) and compared to those previously obtained in high-neuroticism anxiety-prone indivuduals. Although these and hyperthyroids do show indications of similar behavioral manifestations (excessive reactive arousal), both groups are considered to differ regarding empirical referennts of anticipatory arousal (ERSP parameters). A major difference seems to be the absence of a "ceiling effect" in hyperthyroids. This hypothetical phenomenon can be expected on the basis of the inverted U-shaped relation between ERSP amplitude and arousal level. A stronger "distraction" effect associated with increased arousal in anxiety neurotics is postulated and tentatively attributed to covert verbalizations of worry and feelings added to increased awareness of autonomic input. The contention is advanced that similar behavioral manifestations could be distinguishable at the physiological level employed and this might add further insights to diagnostic typologies (e.g., "psychosomatic" vs. "psychoneurotic" patients).