Acta Psychiatr Scand 2020: 141: 374–384
All rights reserved
DOI: 10.1111/acps.13148
© 2020 The Authors. Acta Psychiatrica Scandinavica published by John Wiley & Sons Ltd
ACTA PSYCHIATRICA SCANDINAVICA
Actigraphic patterns, impulsivity and mood
instability in bipolar disorder, borderline
personality disorder and healthy controls
McGowan NM, Goodwin GM, Bilderbeck AC, Saunders KEA.
Actigraphic patterns, impulsivity and mood instability in bipolar
disorder, borderline personality disorder and healthy controls.
Objectives: To differentiate the relation between the structure and
timing of rest-activity patterns and symptoms of impulsivity and mood
instability in bipolar disorder (BD), borderline personality disorder
(BPD) and healthy controls (HC).
Methods: Eighty-seven participants (31 BD, 21 BPD and 35 HC)
underwent actigraph monitoring for 28 days as part of the Automated
Monitoring of Symptom Severity (AMoSS) study. Impulsivity was
assessed at study entry using the BIS-11. Mood instability was
subsequently longitudinally monitored using the digital Mood Zoom
questionnaire.
Results: BPD participants show several robust and significant
correlations between non-parametric circadian rest-activity variables
and worsened symptoms. Impulsivity was associated with low interdaily
stability (r = 0.663) and weak amplitude (r = 0.616). Mood
instability was associated with low interdaily stability (r = 0.773),
greater rhythm fragmentation (r = 0.662), weak amplitude (r = 0.694)
and later onset of daily activity (r = 0.553). These associations were not
present for BD or HCs. Classification analysis using actigraphic
measures determined that later L5 onset reliably distinguished BPD
from BD and HC but did not sufficiently discriminate between BD and
HC.
Conclusions: Rest-activity pattern disturbance indicative of perturbed
sleep and circadian function is an important predictor of symptom
severity in BPD. This appears to validate the greater subjective
complaints of BPD individuals that are sometimes regarded as
exaggerated by clinicians. We suggest that treatment strategies directed
towards improving sleep and circadian entrainment may in the future
be investigated in BPD.
N.M. McGowan1 ,
G.M. Goodwin1,2,
A.C. Bilderbeck1,
K.E.A. Saunders1,2,3
1
Department of Psychiatry, University of Oxford, 2Oxford
Health NHS Foundation Trust, Warneford Hospital, and
3
NIHR Oxford Health Biomedical Research Centre,
Oxford, UK
This is an open access article under the terms of the
Creative Commons Attribution License, which permits
use, distribution and reproduction in any medium,
provided the original work is properly cited.
Key words: borderline personality disorder; bipolar
disorder; actigraphy; impulsivity; mood instability
Niall M. McGowan, PhD, Department of Psychiatry,
University of Oxford, Warneford Hospital, Oxford, OX3
7JX, UK.
Email: niall.mcgowan@psych.ox.ac.uk
Accepted for publication January 5, 2020
Significant Outcomes
• Objectively
•
•
determined rest-activity patterns are strongly correlated with worsened symptoms of
impulsivity and longitudinally monitored mood instability in BPD.
Sleep and circadian features may impact on the chronicity of symptoms in BPD above BD and HCs.
Future studies targeting rest-activity pattern modification in BPD are indicated.
Limitations
• Sample heterogeneity present for gender and number of unemployed individuals.
• Relative small sample size restricts stratification for medication and comorbid diagnoses.
374
Actigraphic patterns, impulsivity and mood
Introduction
Bipolar disorder (BD) and borderline personality
disorder (BPD) are psychiatric disorders that share
overlapping core symptoms of impulsivity and
mood instability. Impulsivity, broadly defined,
comprises a behavioural pattern of disinhibition,
reward-seeking and action without forethought
(1). In both conditions, impulsivity is associated
with deleterious outcomes such as increased
aggression, substance abuse, self-harm and acts of
suicide (2–5). Mood instability is characterised by
bursts of intense affect and marked difficulties in
regulating mood and behaviour (6). In BD and
BPD, poorly managed mood instability predicts
poorer prognosis, greater number of hospital
admissions and suicidal behaviour (7–9). Thus,
explicit treatment of impulsivity (10) and stabilisation of mood (11) should both be considered
targets for improvement.
Sleep disturbance is a widely reported sequela of
several psychiatric disorders and a suggested transdiagnostic contributor to symptom severity and
functional disability (12). In both BD and BPD,
sleep disturbance is associated with symptomatic
relapse (13, 14). Moreover, dysfunctional sleep has
been implicated in several maladaptive neurocognitive processes which underwrite mood and
impulsive behaviour (15, 16) highlighting sleep as a
potential mediating factor and therapeutic target.
A key contributor to healthy sleep is functional
operation of the circadian clock, which orchestrates the appropriate timing of rest and activity
patterns. The clock operates within and between
days, to synchronize (‘entrain’) endogenous circadian rhythms with environmental time signals (i.e.
‘zeitgebers’, particularly light). (17) Monitoring of
night-time sleep and the twenty-four hour rest-activity pattern, using technologies such as wristworn actigraphy, has become increasingly prominent in psychiatry. Several studies monitoring restactivity patterns and circadian biomarkers have
suggested that abnormal circadian rhythm function may be a driver of disordered sleep in BD (13,
18–20). Circadian dysfunction has been postulated
for BPD, but has not hitherto been extensively
investigated (21).
Recently, we identified desynchronised patterns
of heart rate, activity and sleep, in participants
with BD and BPD (14) and correspondingly,
reported an association between desynchrony
and differential mood patterns (22). We also
demonstrated that individuals with BPD exhibit
rest-activity patterns that are suggestive of phase
delayed circadian clock function compared with
stable BD and healthy controls (23). Thus, sleep
and circadian rhythm disruption may be longitudinally specific to BPD, because symptom severity is
chronic, rather than intermittent, as in BD. However, it is not presently clear to what degree these
disturbances are related to symptom severity in
BD and BPD, or whether this relationship differs
between conditions. Our previous work examined
only group-wise actigraphy differences in this sample, and a limited assessment of heart-rate/chestmounted acceleration signals with mood outcomes
over a short-term sampling period (4 days). To
our knowledge, there have been no studies specifically examining how objectively assessed sleep/circadian actigraphy parameters valid over several
weeks are related to impulsive symptoms or longitudinal mood instability in BPD.
Aims of the Study
The current study aimed to investigate the relationship between core symptoms of both BD and BPD
with the circadian structure and timing of the
actigraphy assessed rest-activity rhythm. We
compared individuals with BD, BPD and healthy
volunteers recruited from the general population
in order to differentiate symptom-actigraphy
measured associations in those with psychiatric
disorder to those without. As impulsivity and
mood instability are transdiagnostic features
that are core symptoms in both conditions, the
principal unelucidated question that we aim to
clarify is whether BD and BPD differ in terms of
symptom severity relating to sleep/circadian
rhythm function.
Material and methods
Study design
This study used data from three groups: participants diagnosed with BD, BPD and healthy volunteers, all of who were enrolled in the Automated
Monitoring of Symptom Severity (AMoSS) study
(24) conducted between March 2014 and February
2016. BD and BPD participants were recruited
from out-patient services around Oxfordshire, UK
or from registration lists for other ongoing studies.
Healthy volunteers were recruited from the community. Written informed consent was obtained
from all participants. All procedures contributing
to this work comply with the ethical standards of
the relevant national and institutional committees
on human experimentation and with the Helsinki
Declaration of 1975, as revised in 2008. All procedures were approved by the NRES Committee
East of England—Norfolk (13/EE/0288).
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Mcgowan et al.
Participants
The data presented here consist of measurements
from 87 participants with valid actigraphy recordings: 31 BD (mean age [SD] = 39.2 [12.2] years, 21
females), 21 BPD (34.1 [10.5] years, 19 females)
and 35 healthy controls (HC) matched for age
(39.5 [12.5] years, 24 females). Extensive demographic details of this sample and data quality control procedures for actigraph data processing have
been described previously (23). Demographic and
clinical features of the sample are presented in
Table S1. Participant diagnoses were confirmed
prior to study admission by an experienced psychiatrist (KEAS) using the Structured Clinical Interview for DSM-IV and the International
Personality Disorders Examination (IPDE). Exclusion criteria for HCs were as follows: history of
neurological disorder or head injury, history of
major psychiatric illness and having a first degree
relative with a history of BPD or BD. Exclusion
criteria for BD and BPD were comorbidity of each
diagnosis. Participants with psychiatric disorder
were stable throughout the actigraph recording
period with Altman Self-Rated Mania (ASRM)
scale completed weekly indicating no manic episode in BD. Depressive symptoms were assessed
weekly during the actigraph recording period using
the Quick Inventory of Depressive Symptomatology (QIDS) and were significantly greater in BD
relative to HC, and significantly greater in BPD
relative to HC and BD. Groups were age matched
at study entry but differed in terms of gender composition and employment status (see Table S1).
Actigraphy
Monitoring of rest-activity patterns commenced
on the first day participants were enrolled in the
study. Participants wore GENEActiv Original actigraphs (ActivInsights Ltd., UK) which were worn
continuously on the non-dominant wrist for 28
consecutive days. The actigraphs contained triaxial
accelerometers, which recorded and logged movement throughout the monitoring period at a sampling frequency of 25 Hz. Groups did not differ in
terms of actigraph compliance, season when
recording took place or the proportion of weekdays or weekend days in each record (23).
Exported data were analysed using the validated
GGIR dedicated package (25) for R version 3.4.2
(R Core Team, Vienna). GGIR processes multi-day
raw accelerometer signals and generates standard
parameters used to quantify the circadian rhythmicity of rest-activity patterns previously described
by Van Someren et al (non-parametric circadian
376
rhythm analysis) (26). The following rhythm
parameters were derived: interdaily stability, intradaily variability, relative amplitude, L5 and M10
activity levels and onsets and are described below.
Interdaily stability (IS) indicates how stable restactivity patterns are between days and therefore
reflects the day-to-day consistency of behavioural
routines. It is adversely affected by behaviours and
schedules which result in recurring circadian
misalignment.
Intradaily variability (IV) indicates how fragmented states of rest and activity are within the
24 h day and thus may be considered a measure of
the consolidation of continuous sleep and wake
states. Lower IV values for example emerge from
frequent awakenings during night-time sleep episodes or taking several naps during the day when
one would normally be awake.
Relative amplitude (RA) indicates the amplitude
or robustness of daily rest-activity rhythms. It
measures the difference in mean activity levels over
the most active consecutive 10 h period (M10)
compared with the least active consecutive 5 h period (L5) of the 24 h pattern and is expressed in relative terms for each individual. Lower RA reflects
little differentiation between periods of rest
and activity and therefore a weaker circadian
rhythm of the rest-activity pattern. It is associated
with poor circadian entrainment to oscillating zeitgebers.
M10 and L5 provide additional information
about arousal patterns during the day and night.
For example, lower M10 values correspond with
inactivity during the day while higher L5 values
suggest disturbed sleep. M10 onset and L5 onset
times indicate phase markers of circadian function
corresponding with the onset of activity during the
day and the offset of activity in during the night.
Activity assessed in this manner is a validated measure of circadian phase predicting the circadian
rhythm of melatonin secretion (27). The standard
deviation of daily M10 and L5 activity patterns
and onset times, and RA were also calculated to
provide additional information on variability of
activity, phase, and amplitude during the recording
period.
Assessments
Barratt Impulsiveness Scale. The Barratt Impulsiveness Scale (BIS-11) (28) was used to assess
impulsivity. Self-reported ratings on 30 questions
measuring three domains of impulsivity
(‘attentional impulsiveness’, ‘motor impulsiveness’
and ‘non-planning impulsiveness’) were used to
determine a total BIS-11 score which can range
Actigraphic patterns, impulsivity and mood
from 30 to 120. Higher scores indicate greater
levels of trait impulsivity.
Mood Zoom. The Mood Zoom (MZ) questionnaire was conceived as part of the AMoSS study to
provide a compact daily assessment of mood variability delivered via a smartphone application. The
MZ comprises six mood items: ‘anxious’, ‘elated’,
‘sad’, ‘angry’, ‘irritable’ and ‘energetic’. Participants were asked each day to rate to what extent
the aforementioned words described their current
mood on a 7-point Likert scale ranging from ‘Not
at all’ to ‘Very much’. Participants were recruited
to use the MZ for an initial 3 month period with
the option to remain in the study for 12 months or
longer. The mean length of the monitoring period
for the total sample was 429 days (SD = 239) and
did not differ significantly between groups
(Table S2). Median adherence after the full
12 month observation period was> 79% irrespective of diagnosis or HC status, displaying a robust
acceptability of the instrument (24).
A three-component structure of the MZ questionnaire has previously been described summarising ‘positive’, ‘negative’ and ‘irritability’ factors
which correlate well with standardised measures of
depression (QIDS), anxiety (GAD-7) and mental
health status (EQ-5D) (24). To assess mood instability, we extracted cross-sectional statistics from
each participant’s longitudinal data set of daily
MZ ratings. We used the root mean square of successive differences (RMSSD) to measure mood
instability, which is a measure of variability reflecting both the temporal order and amplitude of the
data (29). Marked differences in mood variability
between these groups using the RMSSD operator
have previously been described (24). In the supplementary material, we report comparisons with
actigraphic variables using differential assessments
of variability: standard deviation (SD), Teager–
Kaiser Energy Operator (TKEO) and Shannon
entropy. The mean of the z-score transformed
RMSSD of each component was used to measure
overall mood instability for each individual during
the study observational period.
Statistical analysis
Partial Pearson product moment correlation coefficients between actigraph parameters and symptom
outcomes, controlling for gender and employment
status, were analysed for each diagnostic group
(i.e. HC, BD or BPD). Covariates inserted were
planned in advance given our previous work indicating differences in these characteristics between
these groups (23). Distribution of data was
inspected using Kolmogorov–Smirnov tests for
normality. Observations deviating from normal
distribution were first log transformed but nonnormality persisted so partial Spearman’s rankorder correlation was used. Group-wise analysis
using Fisher’s r to z transformation was used to
confirm differences in correlation strength between
diagnostic groups and healthy controls. Additionally, we present an exploratory re-analysis of our
previous findings (23) examining whether a classification analysis could discriminate between diagnoses using actigraph measures. The area under
the receiver operating characteristic (ROC) curve
(AUC) was used to visually inspect the relation
between sensitivity and specificity. The Youden
Index (i.e. highest value obtained when calculating
sensitivity + specificity – 1) was used to determine
optimal cut-off values from which the positive prediction value (PPV) and negative prediction value
(NPV) were determined. All analyses were performed in SPSS (IBM) and R version 3.4.2 (R
Core Team, Vienna). A significance threshold of
P < 0.05 was used for all comparisons, and correction for multiple comparisons was applied using
the Benjamini–Hochberg false discovery rate
(FDR).
Results
A summary of correlation results are depicted in
Figure 1. All analyses described here are partial
correlations controlling for gender and employment status (bivariate correlations without covariates are reported in Table S3; partial correlations
including covariates are reported in Table S4).
Correlation strengths did not appreciably differ
between bivariate and partial approaches. Inspection of partial correlation coefficients with covariates inserted revealed strong associations between
sleep/circadian rhythm parameters and symptoms
of impulsivity and mood instability in BPD. These
associations were not found in either the BD participants or HCs. Specifically, in BPD but not HC
or BD, rhythm stability (IS) and rhythm amplitude
(RA) were negatively correlated with both impulsivity (IS: r = 0.663, P = 0.012, RA: r = 0.616,
P = 0.020) and mood instability (IS: r = 0.773,
P = 0.001, RA: r = 0.694, P = 0.006). Thus, less
stable and lower amplitude rest-activity patterns
were associated with greater symptom severity.
Furthermore, mood instability in BPD but not HC
or BD was associated with greater rhythm fragmentation (IV: r = 0.662, P = 0.006), later onset of
daily activity (M10 onset: r = 0.553, P = 0.028)
and greater nocturnal arousal (L5 activity:
r = 0.560, P = 0.028). Representative scatter plots
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Mcgowan et al.
showing associations for IS, IV, RA and M10
onset are presented in Figure 2. Impulsivity and
mood instability were respectively associated with
more variable L5 activity and activity offsets in
BPD indicated by the standard deviation of L5
activity and L5 onset between days (Table S4).
In order to confirm these associations, we performed group-wise assessment of partial correlation coefficients which indicated that the strength
of the relation between symptoms and rest-activity
parameters was significantly greater for BPD than
HC and BD (Table S5). There were no significant
differences in the strength of these associations
between HC and BD. The associations between
rest-activity pattern structure and timing and
mood instability were replicated using SD and
TKEO operators of variability (Figure S1; Tables
S6 and S7) but were not present for entropy (Figure S1; Table S8).
Next, we performed an exploratory classification
analysis to determine whether a bottom-up
approach to actigraphic measures could correctly
distinguish BD and BPD from HC and BPD from
BD. We examined the classification accuracy of
the following actigraph summary variables: IS, IV,
RA, L5 onset, M10 onset, L5 activity and M10
activity. ROC curve parameters (sensitivity and
specificity) and optimal cut-off values are summarised in Table S9. The L5 onset of activity
showed the best classification performance
(AUC = 0.83, good accuracy) between BPD and
HC with the highest sensitivity and specificity. An
L5 onset cut-off of 01:35 h had a PPV of 0.75 (i.e.
probability that participant scoring later had BPD)
and a NPV of 0.83 (i.e. probability that participant
scoring earlier was HC). The performance of BPD
versus BD was fair (AUC = 0.79); an L5 onset cutoff of 01:37 h had a PPV of 0.71 (i.e. probability
that participant scoring later had BPD) and a NPV
of 0.81 (i.e. probability that participant scoring
earlier had BD). Classification accuracy of L5
onset between HC and BD did not perform sufficiently better than chance (AUC = 0.52). The performance of the remaining aforementioned
actigraph summary variables ranged from <0.5 to
0.68 indicating poor classification accuracy.
Discussion
Unstable interdaily patterns (low IS) and weakened rhythm amplitudes (low RA) are associated
with both impulsivity and mood instability in
BPD. Furthermore, mood instability in BPD is
associated with greater fragmentation of rest-activity states (IV), greater nocturnal activity levels (L5)
and phase delayed daytime activity patterns (M10
onset). We believe these are the first reported
results demonstrating an association between
objective measures of sleep and circadian function
and longitudinal symptom severity in BPD. These
associations were not detectable in BD and HC.
Furthermore, group-wise comparison of correlation strengths further confirms these associations
in BPD.
There is little or no previous relevant research in
BPD. The most recent meta-analytic review of the
literature examining sleep disturbance primarily
identified acute polysomnography (PSG) recordings which are limited to single nights (30). These
findings describe greater sleep onset latency, poor
sleep efficiency and shorter sleep duration in BPD
compared with controls (31–33). Each of these
Fig. 1. Correlation between sleep/circadian rhythm parameters and symptoms. Radar plots indicate partial correlation coefficient
strength between rest-activity pattern variables and symptoms of impulsivity and mood instability for healthy controls and diagnostic groups. BPD consistently show stronger association between symptoms and parameters indicating perturbed and delayed rest-activity profile. Negative correlations (e.g. for interdaily stability, relative amplitude and M10 activity) were reversed and renamed for
visual consistency such that higher values uniformly indicate stronger association. Labels enclosed in boxes indicate a negative relation. [Colour figure can be viewed at wileyonlinelibrary.com]
378
Actigraphic patterns, impulsivity and mood
Impulsivity
R = 0.175
Mood instability
R = –0.108
R = 0.013
R = 0.113
R = –0.773**
R = –0.663*
Interdaily stability
Interdaily stability
R = –0.096
R = 0.156
R = 0.031
R = –0.157
R = 0.662**
R = 0.331
Intradaily variability
Intradaily variability
R = 0.369
R = -0.162
R = –0.192
R = –0.344
R = –0.616*
R = –0.694**
Relative amplitude
R = –0.113
Relative amplitude
R = –0.142
R = 0.004
R = 0.539
M10 onset (local time, hh:mm)
R = –0.066
R = –0.553*
M10 onset (local time, hh:mm)
Fig. 2. Scatter plots indicating the relationship between sleep/circadian rhythm parameters and symptoms. Scatter plots representing
the partial correlation analysis conducted between rest-activity variables (IS, IV, RA and M10 onset) and impulsivity and mood
instability are depicted for each group (HC, BD and BPD). * indicates P < 0.05; ** indicates P < 0.01. All P-values are adjusted for
FDR as per Table S4. [Colour figure can be viewed at wileyonlinelibrary.com]
parameters have previously been associated with
mood disturbance (34). However, the longitudinal
picture of sleep is not adequately captured by PSG
and few studies have assessed core symptoms in
parallel with sleep. Actigraphy studies in BPD
are sparse, conducted over short intervals and
similarly limited regarding additional symptom
monitoring (35, 36). Subjective assessments of
chronic sleep disturbance have suggested an
association with worsened BPD symptoms among
community and out-patient groups (37–39). The
present findings indicate that core symptoms are
associated with objectively measured sleep/restactivity patterns. Thus, we propose that disturbances in initiating/maintaining sleep may be an
important exacerbating factor for borderline
psychopathology.
The correlations between worsened symptoms of
impulsivity and mood instability with unstructured
rest-activity patterns, characterised by lower relative amplitude, lower interdaily stability and
greater phase variability within days, suggest that
circadian rhythm disturbance may be an important
impairing factor for BPD symptom management.
Previous qualitative descriptions of sleep habits of
individuals with BPD have emphasised chaotic
patterns and poor adherence to socially normal
bedtimes (40). Recurring circadian misalignment
between habitual bedtimes and social timing
imperatives, also termed ‘social jetlag’ (41), may be
a feature experienced chronically in BPD. Social
jetlag has previously been indicated from actigraphy records in adolescents with BPD (36), and we
previously described delayed circadian phase in the
current BPD participants (23). Delayed phase is an
established risk factor for worsened social jetlag.
Such chronic circadian misalignment may lead to
non-optimal organisation of physiologic and
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Mcgowan et al.
cognitive rhythms relative to time-of-day demands,
so may in turn precipitate impulsive behaviour and
mood instability.
The association between impulsivity and
alteration of sleep/wake activity is unlikely to be
specific to BPD. Indeed, in a previous study of
non-clinical volunteers, higher impulsivity scores
were similarly correlated (42). This trait may also
be important in ADHD (43). Similarly, mood
instability has been associated with lower amplitude rest-activity patterns but thus far has been
measured retrospectively, not prospectively or longitudinally as in our present findings (44, 45). As a
core diagnostic feature of BPD, mood instability
is, by definition, chronically both extreme and clinically salient (46, 47). The subjective complaints of
BPD individuals are sometimes regarded as exaggerated by clinicians. There is regular disagreement
between patient reports and assessment by clinicians which are routinely attributed to distorted
self-perceptions and attributions by patients with
BPD themselves (48, 49). The stronger correlation
with objective measures of sleep/wake disturbance
can be seen as validating the reported experience
of the patients in an interesting way. Individuals
with BPD do endorse greater dysfunctional and
catastrophic beliefs relating to their sleep, but our
data suggest that the impact of sleep-wake disturbance on symptoms is real and substantial (50).
The association of sleep disturbance and abnormal activity rhythms with BD has been described
in multiple systematic reviews of studies employing
actigraphy. The most consistent findings in BD are
hypersomnia, delayed sleep onset latency and
lower sleep efficiency (51–53). However, differential actigraphy patterns have been described during
the manic phase of BD compared with depression,
euthymia and healthy controls. These findings
highlight that mania is correlated with advanced
circadian phase, greater motor arousal and higher
frequency variability of rest-activity patterns (54,
55). Depressed state conversely is associated with
delayed sleep phase indicative of delayed circadian
rhythm phase of entrainment (56). Our BD participant group recorded median values below 11 on
the QIDS and below 6 on AMSR indicating that
they were symptomatic but not syndromally
depressed or manic (23). Concordant with our classification analysis, we note that none of the actigraphic parameters could reliably distinguish
stable BD from HC. The absence of associations
between residual symptoms and actigraphy measures further contrasts with the findings for the
BPD group.
Mood instability is a transdiagnositc feature
common in both disorders. In BPD, it comprises a
380
core diagnostic feature of the disorder typified by
rapid alterations in mood over minutes to hours.
However in BD, the episodicity of mood symptoms is a principal criterion for diagnosis. Studies
involving digital self-monitoring of mood have
reflected these diagnostic differences in the magnitude and frequency of mood alteration. Mood
instability between discrete mood episodes in BD
is diminished (57) and of lower amplitude than
BPD (24). Our measures of mood instability capture short-term variability through successive
observations (RMSSD), general variability of ratings (SD) and instantaneous changes of amplitude
and frequency of the signal (TKEO). Thus, we
observe associations between clinical symptoms
and mood lability that is chronic, intense and
rapidly changing and typical for BPD. Therefore,
a closer association between disturbed rest-activity
patterns and mood instability in BPD may be
expected due to the ecological validity of these
measures of variability reflecting interdaily mood
vacillation in BPD above BD. Other core symptoms of BPD but not BD, such as severe interpersonal dysfunction and unstable self-image may
also enrich this instability of mood. Our entropy
measure was not in the same way associated with
actigraphy parameters in either group. Increased
entropy, which measures unpredictability, has previously been observed over a shorter window in
BD to precede clinically confirmed mood episode
(58). Thus, its utility as a measure of instability
may be limited to proximal switches in mood state.
Future work is indicated in BD to confirm the
potential of shorter time-course measures of mood
instability combined with rest-activity features as
predictors of subsequent mood episodes. A further
consideration is noted between mood instability
and affective instability. While the two terms are
often used interchangeably in the literature (6), different conceptualisations exist for each: affect typically refers to the experience of emotion and is
short-lived whereas mood may last longer and lack
a focused cause. Clearly, these constructs have
implications for symptom measurement, the differentiation of BD/BPD and the contribution of
sleep/circadian rhythm disturbance. Greater
assessment precision achieved through momentary
assessment methods, such as in this study, may in
future be bolstered by contemporaneous logging of
behaviour and environment in order to clarify such
subtleties (11).
Similar to mood, impulsive symptoms differentially expressed between diagnoses may account
for the closer relations to sleep/circadian disturbance in BPD. In BPD, impulsive behaviour such
as repeated engagement in risky (e.g. reckless
Actigraphic patterns, impulsivity and mood
decision-making) or harmful (e.g. self-injury, parasuicidal) activities is persistent. In BD, behaviours
such as risky engagement in pleasurable activities
and psychomotor impulsivity (e.g. restlessness/agitation) are diagnostic criteria for mania implying a
specific association with mood elevation. Thus, the
impulsive modality in BPD is typically chronic and
may reflect a stable trait, while in BD it may be
intermittent, driven by mood state. Furthermore,
differences have been demonstrated in laboratory
decision-making tasks probing impulsivity. Examination of BPD and BD compared with controls
show that greater risk-taking and failure to integrate reward information is a primary deficit in
BPD, not in euthymic BD (59). Studies also indicate that current mood status does not prime
impulsive neurocognitive responding in BPD (60,
61) as would be expected in BD. These differences
may have implications for differential sensitivity to
perturbed rest-activity patterns in BPD over BD.
The direction of effect is not apparent. Clearly, disturbed sleep may lead to greater impulsive action
(62). Alternatively or additionally maladaptive
goal-directed behaviour and intertemporal perspectives may lead to later bedtimes and irregular
circadian entrainment (63). Moreover, the manner
in which impulsivity was assessed may further
account for different relations between diagnoses.
The BIS-11 is the most widely used instrument for
the assessment of impulsivity in clinical populations but a very recent examination of its reliability
in euthymic BD suggests the original item structure
may not be optimal (64). Although BIS-11 scores
in BD and BPD were similar in the current study
(BPD marginally higher, but not significantly different) the instrument may show greater item proximity to the experiences of individuals with BPD
compared to BD which may also contribute to the
closer associations detected.
The current study goes beyond previously
reported group-wise findings in this sample (23) by
examining if symptom severity is associated with
sleep/circadian patterns and whether this appears
in a diagnostic dependant manner. Our previously
reported results raise several implications for the
interpretation of findings. Notably, despite a closer
association between symptoms and interdaily stability and intradaily variability in BPD, we previously show no differences in group mean score.
Relative amplitude was similarly not lower in BPD
but there was greater within-group variability on
this measure. As the association with symptoms is
at a within-group level, we suggest a greater reactivity to circadian misalignment and larger proportion of individuals with weak entrainment may
drive findings rather than overt between-group
differences. Our previous findings show a delayed
rest-activity pattern in BPD relative to BD and HC
through the later onset of L5 and M10 (23). Moreover, our classification analysis of actigraph
parameters confirmed that later L5 onset discriminated BPD from BD and HC indicating good sensitivity and specificity. However, L5 onset was not
significantly associated with symptoms in BPD
and M10 onset was only associated with mood
instability. Delayed circadian phase also predisposes lower stability and weak rhythm amplitude
in the context of poor zeitgeber entrainment. Thus,
we further propose that low circadian amplitude
and greater misalignment between days in individuals with greater liability to delayed phase (as in
BPD) may drive worsened symptoms even if IS
and RA differences are not apparent between
groups.
The associations described here indicate several
translational opportunities for BPD treatment.
Stabilisation and consolidation of rest-activity
rhythms might be considered a primary target for
adjunctive treatment if indeed symptoms are in
part driven by sleep and circadian rhythm disturbances. Preliminary work using bright light therapy in BPD has shown promise resulting in
activity phase advance and synchronisation of
sleep times (65), and augmentation of antidepressant response when treated with SSRIs (66). Interpersonal and social rhythm therapy (IPSRT) (67)
was originally conceived with the purpose of regularising daily patterns in BD so as to mitigate a
low threshold for rhythm disruption and subsequent mood decompensation. IPSRT-inspired
approaches may be additionally beneficial in supporting individuals with BPD where such social
rhythm instability is apparent. Furthermore, as
maladaptive sleep cognitions are common in BPD
(50) and this may further perpetuate the severity of
insomnia, cognitive behaviour therapy for insomnia (CBT-I) could be used to address dysfunctional
beliefs and behaviours about sleep which has been
shown to mediate improvement of depression and
psychological well-being (68, 69).
Limitations
Although our analyses of between group differences
attempted to control for covariates, there was significant heterogeneity of sample demographics
between groups, with a preponderance of females
and unemployed individuals in the BPD, compared
with BD and healthy groups. It is also difficult to
control for comorbid diagnoses and divergent medication use in studies of this sample size. Our key
findings were at the level of diagnostic group
381
Mcgowan et al.
difference, and thus, our approach is limited in providing any within-subject conclusions. Future studies with greater experience sampling multiple times
each day will allow enhanced characterisation of the
intradaily dynamics of mood instability within individuals and its relation to adjacent sleep episodes.
Further work is also needed to advance the understanding of the relation between sleep and BPD
specific symptoms (e.g. interpersonal dysfunction,
identity disturbance and abandonment fears) which
also explicitly exclude sleep disorders or other
comorbid disorders affecting sleep. Although the
prospective nature of mood monitoring suggests
prima facie evidence for long-term effects of sleep
and circadian rhythm disturbance on symptoms, a
causal direction of effect has not been established
by this study.
To conclude, the current results show a very
close association between disrupted sleep and misaligned circadian rest-activity rhythms and symptoms of impulsivity and mood instability in BPD.
An initial 28 day actigraphy record correlated
robustly in BPD with impulsivity, and mood outcomes which were prospectively measured over
several months. This suggests that untreated restactivity rhythm disturbances may associate with
worsened clinical course for participants with
BPD. Perhaps surprisingly, given the historical
interest in BD and circadian function and the
symptom overlap with BPD, stable BD patients do
not show similar associations. However, small
sample sizes limit the generalisability of findings
and replication is necessary. In contrast to the evidence showing beneficial outcomes for chronotherapies in BD (70), future studies targeting sleep and
circadian rhythm stabilisation in BPD may also
produce significant benefits for its treatment.
Acknowledgements
This study was supported by the Wellcome Trust through a
Centre Grant no. 98,461/Z/12/Z. ‘The University of Oxford
Sleep and Circadian Neuroscience Institute (SCNi)’. This work
was also funded by a Wellcome Trust Strategic Award (CONBRIO: Collaborative Oxford Network for Bipolar Research to
Improve Outcomes, Reference number 102,616/Z). This
research was supported by the National Institute for Health
Research Oxford Health Biomedical Research Centre. The
views expressed are those of the authors and not necessarily
those of the NHS, the NIHR or the Department of Health.
Disclosures
Prof Goodwin is a NIHR Emeritus Senior Investigator holds
shares in P1vital and P1vital Products and has served as consultant, advisor or CME speaker in the last 3 years for Allergan, Angelini, Compass pathways, Johnson & Johnson,
Lundbeck (/Otsuka or/Takeda), Medscape, Minervra, P1Vital,
382
Pfizer, Sage, Servier, Shire, Sun Pharma. Dr. Bilderbeck
receives salaries from P1vital Ltd. Dr. McGowan and Dr
Saunders report no competing interests.
The views expressed are those of the author(s) and not necessarily those of the NHS, the NIHR or the Department of
Health.
Data availability statement
The data that support the findings of this study are available
from the corresponding author upon reasonable request.
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Supporting Information
Additional Supporting Information may be found in the online
version of this article:
Figure S1. Correlation between sleep/circadian rhythm parameters and MZ variability using SD, TKEO and Shannon
entropy.
Table S1. Summary of demographic and clinical features of
sample
Table S2. Summary of BIS-11 and MZ data.
Table S3. NPCRA parameter bivariate correlations with
impulsivity and mood instability.
Table S4. NPCRA parameter partial correlations with impulsivity and mood instability.
Table S5. Group-wise comparison of partial correlation coefficients.
Table S6. MZ variability (SD) and NPCRA variables.
Table S7. MZ variability (TKEO) and NPCRA variables.
Table S8. MZ variability (Entropy) and NPCRA variables.
Table S9. Discriminant properties of actigraph measure for
diagnosis using ROC curve classification analysis.