Veeha Verma
Remedial Blog Post for Quiz 6
Schizophrenia
has perhaps one of the biggest impacts on cognition, leading to severe
cognitive impairment. No case is exempt, the two going hand in hand. However,
the factors within the illness that lead to this impairment are not well known
or discussed. Due to the sleep disorganization and disruption, the role of the
circadian rhythm comes into question. A prolonged disturbance in the exposure
to light and dark cycles is known to have extreme effects on cognitive
representation, memory and learning. We will now look at whether and what the
extent of the influence of the circadian rhythm on cognitive impairment is.
To
begin lets first look at what the circadian clock and the circadian rhythm are.
The circadian clock may be thought of as an endogenous clock which runs on a
24-hour cycle, the central mechanism of which is situated in the
suprachiasmatic nucleus (SCN) of the hypothalamus in mammals. This rhythm of
physiological and cellular processes is modulated and susceptible to external
cues in the form of light, which coordinates internal time with environmental
changes. The circadian rhythm is any biological process that shows “endogenous,
entrainable oscillation of about 24 hours”. Sleep disturbances are a
characterizing feature of schizophrenia, some believing it is more important to
treat before the actual illness. On the other hand, cognitive functioning
itself is closely related to the day-night cycle. The periods of sleep and
wakefulness thus play a crucial role in the synchronization with the external
world and temporal alignment. So how does this express itself in schizophrenia?
The first signs of cognitive impairment begin to show at the very outset of
psychosis. The effects of this are not localized, affecting the generalized
mental faculties useful in effective negotiation of external activities. These
activities could include learning, remembering, planning and strategy formation, as an effect of
the specific higher mental processes being disrupted by schizophrenia - working
memory, inhibition, memory consolidation and information-processing speed. Most
importantly this impairment is a very strong predictor for later social and
occupational dysfunction, making intervention in this field of primary
importance.
So
let’s break down the exact role of the circadian clock in this. To study its
affects and possible remediation, Bromundt and colleagues worked with a
sample of “well-characterized” patients with schizophrenia (n=14) by having them
wear actigraphs (“Actigraphy is a non-invasive method of monitoring human
rest/activity cycles”) for a three-week period, while also monitoring melatonin
secretion before and after sleep on several occasions throughout. Patients were
entrained to the regular sleep cycle, asleep at night and awake during the day,
removing the confound of gross disruptions of circadian activity frequently
noted in mental health patients. Hence, circadian disturbances showed in
smaller ways, with increased night activity and irregular melatonin secretion
in certain patients. In cognitive tests before and after the actigraphy study,
results remained mostly stable. The group with a normal circadian rhythm
performed within the normal range of published data. In comparison, the group
with disrupted circadian cycles performed worse on all but one of the cognitive
tests (the tests used were verbal fluency, the Stroop test and the Trail Making
test). Interestingly, the study showed that in all patients’ large associations
between day and night activity ratio and the cognitive measures. Effect sizes were
ranging from 0.66 to 0.83, however, no association between the severity of the
symptoms or the duration of the illness was seen. Thus, a specific causation
link is observed between abnormalities in the circadian rhythm and impairment
of cognitive abilities in schizophrenia.
The
study however, has certain limitations. For instance, it doesn’t specify what
it means by “well-characterized” patients. It doesn’t standardize duration of
illness or the kind of schizophrenia being exhibited. Further, the sample size
is quite small within itself, if then broken into sub-groups it is hard to draw
conclusions on such few specimens. However, the basis of these findings appear
sound and this data could have great value in the future. Follow-up studies
should be conducted so that intervention on this basis can be developed.
Bibliography:
Circadian rhythms and cognition in
schizophrenia. Available from:
https://www.researchgate.net/publication/51692459_Circadian_rhythms_and_cognition_in_schizophrenia
[accessed May 03 2018].
Comments
Post a Comment