Endogenous hyperthermia in normal human subjects: I. Experimental study of evoked potentials and reaction time

Abstract

Previous work on awake guinea pigs and rats in the authors' laboratory revealed that microwaveinduced elevations of brain temperature (.:lTs from 1 0 to 3 0 C over resting baselines) are associated with reliable reductions in latencies of flash-evoked brain potentials' (EPs). To assess the generality of this finding in the normal human being, and to avoid the ethical problem of whole-body human exposure to an intense microwave field, .:lTs were induced endogenously by vigorous exercise and by insulative and vapor-barrier clothing. Twenty male athletes, 18 to 22 years of age, were randomly but equally divided into counterbalanced experimental and control groups for a single 3-h morning or afternoon session of measurements. During baseline measures, EPs of three types were observed: flash-evoked N1, pattern-reversal P100, and event-related P300. In addition, simple reaction times (RTs) to photic stimulation were recorded. All measures were repeated after sham warming of the 10 control subjects and after tympanically indexed brain temperatures of the 10 experimental subjects were elevated by an average of 1.2 0 C above control values. EP and RT latencies were reliably reduced in association with the .:lTs, the mean reductions ranging from 3% to 9%. The data on the human flash-evoked N1 component compare favorably with data recorded from rats and guinea pigs that have undergone exogenous elevations of temperature by microwave irradiation. The data on RTs and other EP components are consistent with the thesis that human CNS activity in general is accelerated during a modest bout of whole-body hyperthermia.More than half a century has passed since Hoagland hypothesized that elevation of brain temperature is associated with acceleration of catalytic events that may represent the rate-limiting step in biochemical reactions (Hoagland, 1933). The predicted result is an increase in propagation velocity of nerve impulses. Earlier and sub-

Brain activity and fatigue during prolonged exercise in the heat

“…The present results from exercising humans are consistent with earlier reports of animals and human patients indicating that hyperthermia alters brain activity as reflected by EEG recordings and sensory-evoked potentials [10,11,22,27]. In a study of heat stroke patients, Mustafa et al [22] showed that brain stem auditoryevoked potentials displayed characteristic changes in their mid-latency response at critical high temperatures.…”

Anxiolytic- and Antidepressant-Like Profile of ATC0065 and ATC0175: Nonpeptidic and Orally Active Melanin-Concentrating Hormone Receptor 1 Antagonists

“…Therefore, it is conceivable that ATC0065 and ATC0175 may exert their anxiolytic and antistress effects by attenuating stress-induced increases in HPA function. It is of note that hyperthermia induced by anticipatory anxiety is a well described phenomenon in humans (Reeves et al, 1985) and that autonomic hyperactivity is one of the items in the diagnosis of generalized anxiety disorders mentioned in Diagnostic and Statistical Manual of Mental Disorders,4th Edition. Therefore, MCHR1 antagonists may ameliorate not only emotional aspects but also somatic symptoms observed in patients with anxiety disorders.…”

Exploring exercise as an avenue for the treatment of anxiety disorders

“…This hypothesis has been largely unsupported in empirical work [90]. For example, several studies have found a positive rather than an inverse relationship between body temperature and anxiety ratings when experimentally manipulating body temperature changes during exercise [90–92]. Petruzzello et al found that self-reported anxiety immediately following exercise was higher among those randomized to a warm running condition that induced higher body temperatures than those who exercised in neutral or cool conditions [91].…”