Rh Vandenhoofdakker

Endogenous and exogenous components in the circadian variation of core body temperature in humans

Core body temperature is predominantly modulated by endogenous and exogenous components. In the present study we tested whether these two components can be reliably assessed in a protocol which lasts for only 120 h. In this so‐called forced desynchrony protocol, 12 healthy male subjects (age 23.7 ± 1.4 y) were subjected one by one to an artificial light/dark cycle of 20 h (10 lux vs. darkness). Core body temperature was measured continuously. The temperature data were analysed by an iterative method based on the assumption that the endogenous and exogenous components contribute to body temperature in an additive way. The results show that the average temperature curve is an almost perfect addition of the two components. The endogenous component differs from a sinusoid, and the relative contributions of the endogenous and exogenous components to the raw temperature curves differ substantially between the subjects. The average amount of unexplained variance in the individual data was 17%. Averaging of the body temperature curves over subjects reduced the unexplained variance to only 2%. This reduction in unexplained variance upon averaging over subjects must be due to the fact that most of the variance is either differently dependent on circadian phase for the various subjects or not dependent on circadian phase at all. The circadian pacemaker component revealed an average value of tau of 24.30 ± 0.36 h, which is consistent with recent findings in the literature. We conclude that a short forced desynchrony protocol is sufficient for the distinction between the masking and pacemaker components of core body temperature. The same protocol can be used to study the influence of these components on all kinds of other physiological and psychological signals.

Stress-induced changes in circadian rhythms of body temperature and activity in rats are not caused by pacemaker changes

Previous work has shown that social stress in rats (i.e., defeat by an aggressive male conspecific) causes a variety of behavioral and physiological changes including alterations in the daily rhythms of body temperature and activity. To study the role of the circadian pacemaker in these stress-induced changes, three experiments were performed, successively addressing pacemaker period, phase, and sensitivity to light. In all experiments, rats were subjected to social stress by placing them in the home cage of a dominant conspecific for 1 h. This was done on 2 consecutive days, between the second and fifth hours of the activity phase. Experimental animals were attacked by the resident and lost the fight as indicated by submissive behavior. Control animals were placed in an unfamiliar but clean and empty cage for 1 h. In Experiment 1, the effects of social stress on the period of the free-running activity rhythm were studied. Rats were individually housed under constant dim red light. Activity was measured with infrared detectors. Social defeat caused a reduction of activity for a number of days, but the period of the free-running rhythm was not affected. In Experiment 2, the authors studied whether social defeat induced acute phase shifts. Body temperature and activity were measured by means of radiotelemetry with in traperitoneally implanted transmitters. After the social interactions, experimen tal animals were kept under constant dim red light. Social stress caused a profound reduction in the amplitude of the body temperature and activity rhythm, but no significant phase shifts occurred. In Experiment 3, the authors studied whether social defeat affected the circadian pacemakers sensitivity to light given that the size of light-induced phase shifts is thought to reflect pacemaker amplitude. Again, body temperature and activity were measured by means of telemetry. After double social defeat, animals were kept under continu ous dim red light. One day after the second conflict, animals were subjected to a single 1-h light pulse (300 lux) at circadian time 14. The light pulse induced a phase delay of the body temperature rhythm, but there were no significant differences between the stress and control groups. The data indicate that stress- induced changes in activity and temperature rhythm, as well as behavioral and physiological changes found in earlier experiments, are not caused by changes in the circadian pacemaker. More generally, the data support the notion that overt rhythms are not always a reliable indication of pacemaker function.

ON THE CONTRIBUTION OF SLEEP WAKE PHYSIOLOGY TO THE EXPLANATION AND THE TREATMENT OF DEPRESSION

Physiological exploration has disclosed profound disturbances in the regulation of sleep in depression. The finding that depression can be relieved or intensified by manipulation of sleep has inspired the investigation of the possible pathogenetic significance of these dysregulations. Three hypotheses play a leading role in this context: the “phase‐advance”, the “S‐deficiency” and the “acetylcholine‐monoamine imbalance” hypothesis. They explain the therapeutic effects of a variety of sleep wake manipulations as consequenses of the normalization of depressogenic sleep regulation disturbances.

Early light treatment can prevent an emerging winter depression from developing into a full-blown depression

The administration of light at the development of the first signs of a winter depression appears to prevent it from developing into a full-blown depression. Not a single patient from a group of 16 treated this way became severely depressed during the remaining part of the winter season, whereas 5 out of 11 from the non-treated control group did.

Prediction of clinical change by ethological methods

The aim of this paper is to show that ethology may contribute to the search for early indicators of clinical changes in depression. Three studies are presented. One study deals with the prediction of treatment outcome over 10 weeks and the other two with the prediction of the acute clinical response to total sleep deprivation (TSD). In each study a number of behaviours were observed, as displayed during a baseline psychiatric interview by the patients as well as the psychiatrist. In this report, the predictive potency of directly observed behaviours is compared to the predictive value of global clinical measures of psychomotor activation. The behaviours of the patients were interpreted as “relational” and “nonrelational” behaviours. The relational behaviours (i.e., variation in looking, yes‐nodding, gesturing) occurred less, the nonrelational behaviours (i.e., intensive body touching, head movements) occurred more in responders than in nonresponders to 10 weeks of treatment. Also in the TSD studies body touching was positively related to improvement. Global clinical assessment of psychomotor activation could not be related to outcome. The advantages of the observational methods are discussed.

OBSERVED BEHAVIORS DURING CLINICAL INTERVIEWS PREDICT IMPROVEMENT IN DEPRESSION

A considerable percentage of depressed patients do not respond to antidepressive treatment. Early indicators of prognosis are needed. The aims of this study are to examine (a) whether the interpersonal behavior of patients and psychiatrist, as assessed by means of direct observation of behavior during a baseline clinical interview, might have predictive value with respect to therapeutic outcome and (b) which predictive potency measures of psychomotor activation, as assessed by less refined methods, such as global clinical judgment, might have. In the analysis used, speech-pause behavior was taken as the basic structure of the interaction. The relations of other behaviors such as looking and hand and head movement with this structure were determined. Evidence is presented that in a group of 31 depressives, improvement after a period of 10 weeks was related to observed behaviors during a baseline interview. The behaviors of the patients are interpreted as “relational” or “nonrelational.” The relational behaviors (i.e., looking yesnodding, gesturing) occur less in patients who will improve, whereas the nonrelational behaviors (i.e., intensive body touching, head movements) occur more in these patients. The nonrelational behaviors are presumed to be indicative of the state of arousal. The predictive potency of these variables could not be explained by their relationship with the baseline severity of depression, which in itself also predicted improvement. Moreover, global clinical assessment of psychomotor activation (i.e., retardation and agitation) could not be related to outcome.

SLEEP DISORDERS IN DEPRESSION

Recently some hypotheses explaining sleep disturbances in depression have been proposed. One hypothesis assumes an advanced phase position of the circadian pacemaker controlling a.o. REM sleep (REMS) production. In another a deficiency of process S is proposed. In this paper the sleep of depressed patients and healthy subjects is compared with respect to REMS production and EEG power density (a possible reflection of process S). Data were derived from the literature and from own experiments. The results provide support only for the S deficiency hypothesis.

SPECTRAL-ANALYSIS OF THE SLEEP EEG OF DEPRESSED-PATIENTS BEFORE AND AFTER TOTAL SLEEP-DEPRIVATION

Sleep electroencephalography in depressed patients reveals many signs of disrupted sleep, like long sleep latency, frequent awakenings, reduced amounts of time spent in the sleep stages 3 and 4, and early morning wakefulness. Upon total deprivation of sleep for one night, many patients experience an unexpected alleviation of their depression, which usually lasts until the subsequent sleep period. Attempts have been made to explain these changes of mood to result from induced changes in sleep physiological mechanisms. Such attempts can roughly be categorized in two classes. One class of hypotheses concerns proposed disturbances in circadian sleep control (i.e. the timing of sleep is inappropriately controlled), the other class concerns postulated disrupted homeostatic sleep control (i.e. the intensity of sleep is inappropriately controlled). For both types of theoretical approaches data have been published which are consistent with the hypotheses as well as data which are not.

ATTUNEMENT OF NONVERBAL BEHAVIOR BETWEEN DEPRESSED-PATIENTS AND A PSYCHIATRIST AT ADMISSION IS RELATED TO PERSISTENCE OF DEPRESSION

According to interpersonal theories on depression, the type of interaction between depression-prone subjects and their social environment plays a causal role in the development and course of depression (e.g. Coyne et al.). So far, interpersonal theories have been tackled mostly by psychometrical methods. However, non-verbal behaviour plays an important role in human social interactions. It is assumed that 60-65% of human communication is non-verbal. Ethological observations have shown that non-verbal interpersonal behaviour of depressed subjects, as assessed prior to treatment, is related to treatment-response or subsequent course of depression. These results are in line with an interpersonal approach of depression.