Research report
The quantitative assessment of motor activity in mania and schizophrenia

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Abstract

Background

Increased motor activity is a cardinal feature of the mania of Bipolar Disorder (BD), and is thought to reflect dopaminergic dysregulation. Motor activity in BD has been studied almost exclusively with self-report and observer-rated scales, limiting the ability to objectively quantify this behavior. We used an ambulatory monitoring device to quantify motor activity in BD and schizophrenia (SCZ) patients in a novel exploratory paradigm, the human Behavioral Pattern Monitor (BPM).

Method

28 patients in the manic phase of BD, 17 SCZ patients, and 21 nonpatient (NC) subjects were tested in the BPM, an unfamiliar room containing novel objects. Motor activity was measured with a wearable ambulatory monitoring device (LifeShirt).

Results

Manic BD patients exhibited higher levels of motor activity when exploring the novel environment than SCZ and NC groups. Motor activity showed some modest relationships with symptom ratings of mania and psychosis and was not related to smoking or body mass index.

Limitations

Although motor activity did not appear to be impacted significantly by antipsychotic or mood-stabilizing medications, this was a naturalistic study and medications were not controlled, thus limiting conclusions about potential medication effects on motor activity.

Conclusion

Manic BD patients exhibit a unique signature of motoric overactivity in a novel exploratory environment. The use of an objective method to quantify exploration and motor activity may help characterize the unique aspects of BD and, because it is amenable to translational research, may further the study of the biological and genetic bases of the disease.

Introduction

Increased motor activity is a cardinal feature of mania, characterized in the Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) as an “increase in goal-directed activity… or psychomotor agitation” (American Psychiatric Association, 1994). Manic patients often report that they have more energy than usual and are observed to be physically restless, fidgeting, and changing posture and position frequently. Excessive motor behavior is a key manifestation of inhibitory failure in Bipolar Disorder (BD); individuals with BD have difficulty inhibiting inappropriate or excessive sensory responses, thought, and behaviors. As is thought to be true of inhibitory deficits in general, markedly increased motor activity probably reflects dysregulation of dopamine in the brain, particularly increased extracellular dopamine in subcortical structures which receive direct projections from frontal areas (Weissenborn and Winn, 1992).

Studies of motor overactivity in BD have typically used self-report and observer-rated symptom scales. Symptom ratings may not be the most sensitive means of measuring motor activity, as clinician observations and self-reports of physical activity can be unreliable (Sims et al., 1999). The use of an accelerometer to objectively measure physical activity has been informative in studying the circadian rhythms and everyday activity level of medical populations (Bussmann et al., 1998, Schasfoort et al., 2003, Sims et al., 1999, Sisto et al., 1998) including psychiatric patients (Dubbert et al., 2006, Faulkner et al., 2006, Teicher, 1995, Teicher et al., 1986). Recent advances in ambulatory monitoring such as the LifeShirt System (VivoMetrics, 2002) have made it possible to collect physical activity data via a 2-axis centrally mounted accelerometer. This approach has advantages over the more commonly used methods of wrist or ankle-mounted accelerometers because it measures “whole body” movements (Godfrey et al., 2008) and not just isolated motion of an arm or leg. Accelerometers “have become the preferred choice for continuous, unobtrusive, and reliable method in human movement detection and monitoring” (Godfrey et al., 2008) (p. 1369). In particular, the LifeShirt accelerometer has been previously shown to sensitively classify the unique locomotor activity pattern (shuffling gait) of patients with Parkinson's Disease, supporting the utility of this technology in characterizing and distinguishing motor behaviors (Keenan and Wilhelm, 2005).

The aim of this investigation was to assess motor activity in BD patients who were hospitalized in the manic phase of their illness and compare them with acutely ill schizophrenia (SCZ) patients, as part of a larger investigation on exploratory behavior in human and animal models of psychiatric disease (Perry et al., 2009). Motor behavior was assessed using ambulatory monitoring, while subjects were exposed to a novel environment designed to stimulate exploration. This newly developed paradigm, the Human Behavioral Pattern Monitor (BPM) (Perry et al., 2009, Young et al., 2007), is a human analog of the classic animal “open field” test and is based upon the rodent BPM originally developed by our colleagues (Geyer et al., 1986). We hypothesized that manic BD patients would exhibit increased levels of motor activity compared to both SCZ patients and healthy volunteers. We also compared our physiologic measure of activity to scores from the Young Mania Rating Scale (YMRS) (Young et al., 1978), to assess the relationship between the objective activity measure and symptom ratings.

Section snippets

Participants

The University of California, San Diego (UCSD) School of Medicine institutional review board approved the study. 28 individuals (15 M) with BD, Current Episode Manic participated, along with 17 individuals (11 M) with SCZ and 21 healthy comparison subjects (NC) (10 M). BD and SCZ patients were tested within an average of 96 h of admission to the psychiatric service at the UCSD Medical Center while they were highly symptomatic. Diagnosis of the BD and SCZ patients was obtained using the

Motor activity across groups

The mixed ANOVA on motor activity with education as a covariate revealed a strong main effect of diagnostic group [F (2, 59) = 6.5, p = .003], no main effect of session epoch, no main effect of smoking status, and a trend towards a group-by-epoch interaction [F (4,118) = 2.2, p = .08]. No other two- or three-way interactions were statistically significant. Fig. 1 shows a slight decrease in motor activity across the session in the BD group relative to the other two groups. Planned comparisons indicated

Discussion

This study quantified motor activity in hospitalized manic BD patients and compared them to hospitalized SCZ patients, using ambulatory monitoring technology and a novel paradigm designed to measure human exploratory behavior, the BPM. BD patients showed markedly high motor activity throughout the majority of the exploratory session. Fig. 1 shows that, unlike the two other groups, BD patients' activity appeared to decrease in the final 5 min, perhaps suggesting habituation to the novel

Role of funding source

This work was supported by a grant from the National Institute of Mental Health (NIMH) (R01-MH071916) and a grant from the National Alliance of Research on Schizophrenia and Depression (NARSAD). The NIMH and NARSAD had no further role in the study design; in the collection, analysis, and interpretation of data; in the writing of the manuscript; and in the decision to submit the manuscript for publication.

Conflict of interest

AM reports a financial relationship with the manufacturer of the LifeShirt System, Vivometrics. BH, MP, MG, JY and WP report no biomedical financial interests or potential conflicts of interest.

Acknowledgments

The authors thank Rebecca Wershba and Eliza Ferguson for their contributions to this study.

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