Pending enough primary studies, we invite reviews on this topic to be conducted. Alternatively we will endeavour to conduct our own review to fill this gap in the Library.

October 2020

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Functional laterality refers to a natural asymmetry in left or right-side dominance, for example in terms of handedness, or brain function. Handedness refers to the preference for using one hand over the other for certain tasks. Right-handed people show increased dexterity in their right hand, left-handed people show increased ability the left hand. People may also be ‘mixed’ handed and show different hand preference for different tasks. Listening tasks can be used to assess language lateralisation. People with schizophrenia may show differences in handedness or footedness, as well as altered visual and auditory dominance that may reflect abnormalities in brain laterality and dominance.

What is the evidence for altered functional laterality?

High quality evidence shows that people with schizophrenia are more likely to be left or mixed-handed than people without schizophrenia, including people with other psychiatric disorders. Moderate to high quality evidence suggests this finding is similar for males and females. Moderate to high quality evidence suggests people with schizophrenia have less right-ear dominance, which may be most apparent in people who experience auditory hallucinations. Moderate to low quality evidence suggest people with schizophrenia show an absence of normal leftward asymmetry in the planum temporale and Sylvian fissure brain regions, and an excess rightward asymmetry in the superior temporal gyrus (particularly posterior). There is also a higher frequency of abnormal (reversed) asymmetry in the frontal and occipital lobes.

February 2022

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Catatonia was originally categorised as a subtype of schizophrenia, but it is found in people with other medical, neurological, and psychiatric disorders. Catatonia is characterised by repetitive non-goal-directed movements or goal-directed movements that are executed in an idiosyncratic way. Other forms of catatonia include immobility, mutism, staring, and rigidity. Tardive dyskinesia is a ‘hyper-kinetic’ (excessive movement) disorder, characterised by jerky, involuntary movements, usually of the face and/or limbs. Parkinsonism is another common movement disorder associated with schizophrenia and is a ‘hypo-kinetic’ (reduced movement) disorder, characterised by slowness of movement and rigidity. These movement disorders are associated with antipsychotic medications but can arise independent of medication status.

What is the evidence for movement disorders in schizophrenia?

Moderate quality evidence finds the overall prevalence of extrapyramidal symptoms in people with schizophrenia taking antipsychotics is around 37%. Parkinsonism prevalence is 20%, akathisia prevalence is 11%, catatonia prevalence is 10%, and tardive dyskinesia prevalence is 7%. Non-white ethnicity and the presence of early extrapyramidal symptoms is associated with a small to medium-sized increase in the risk of tardive dyskinesia in patients treated with antipsychotics. There were no moderating effects of age, sex, or medication dose.

Moderate to high quality evidence finds around 17% of people with schizophrenia who are antipsychotic-naïve show symptoms of parkinsonism, and 9% show symptoms of dyskinesia. This corresponds to a large increase in the risk of dyskinesia and parkinsonism when compared to controls. There was also a small increase in these symptoms in first-degree relatives of people with schizophrenia.

February 2022

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Neurological soft signs (NSS) are neurological abnormalities that can be identified by clinical examination using valid and reliable testing measures. They are referred to as ‘soft’ because they not related to a specific brain area, or part of a defined syndrome. Categories of NSS are commonly grouped into three categories; integrative sensory functioning, motor coordination, and complex motor sequencing. Integrative sensory functioning includes impairments in sensory perception such as audio-visual integration or tactile recognition. Motor coordination involves general coordination, balance and gait. Complex motor sequencing involves complex motor tasks, such as repetitive alternating hand positions.

What is the evidence for NSS?

Moderate to high quality evidence suggests medium to large effects of increased NSS in people with schizophrenia or first-episode psychosis compared to people without a psychiatric disorder (controls). There is a small and less widespread effect when comparing people with a first-degree relative with schizophrenia to controls. Compared to people with bipolar disorder and no psychotic symptoms, moderate to high quality evidence shows a small to medium-sized effect of more NSS in people with schizophrenia on motor coordination tasks only.

There are medium-sized associations between increased NSS scores and increased symptom severity and poorer cognitive performance in people with schizophrenia. Both people with remitting or chronic schizophrenia showed improvements in NSS over time, although remitting symptoms were associated with greatest NSS improvements. Increased severity of NSS in people with schizophrenia was associated with; reduced activation of the basal ganglia and inferior frontal cortex, increased activation of the superior temporal gyrus, reduced grey matter volume in the precentral and inferior frontal gyri and thalamus, and reduced white matter volume in the middle temporal and cerebellum regions.

February 2022

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The olfactory system is the sensory system used to interpret and perceive smell, which may be dysfunctional in people with schizophrenia. Olfactory functioning is hierarchical and involves lower-order processing (detection of the stimulus) and higher-order processing (discrimination and identification of the stimulus). Odour detection occurs at the lowest chemical concentration needed to register an odourant. Odour discrimination involves comparing the differences between multiple stimuli, judging odours as pleasant or unpleasant, or comparing the relative concentration of odours. Odour identification draws on a person’s knowledge and memory to correctly label the smell.

What is the evidence for altered olfactory functioning in people with schizophrenia?

Moderate to high quality evidence suggests a medium to large effect of impaired odour detection, identification, and discrimination in people with schizophrenia compared to people without schizophrenia. A longer duration of illness, taking first generation rather than second generation antipsychotics, and older age were all associated with more impairment in patients. Being male or a smoker were related to less impairment in patients.

Moderate to high quality evidence suggests impaired olfactory identification, but not acuity, in people at high clinical or high familial risk of schizophrenia. Moderate quality evidence shows no differences in olfactory functioning between people at clinical high-risk of psychosis who made the transition to psychosis compared to people at clinical high-risk of psychosis who did not make the transition to psychosis.

March 2022

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Pain is defined by the International Association for the Study of Pain (IASP) as “an unpleasant sensory and emotional experience associated with actual or potential tissue damage” and pain is perceived as both a sensory and emotional experience. There is an important distinction between the body’s responses to pain (nociception) and the subjective experience of pain. Measured outcomes of pain perception include pain reactivity, sensory threshold, pain threshold, and pain tolerance, as well as self-reporting of the pain experience.

What is the evidence for pain sensitivity?

Moderate to high quality evidence suggests schizophrenia is associated with a significantly reduced pain response following nociceptive stimuli in several modalities that is unrelated to outcome measure, modality, medication status, or disease state. Physiological responses to nociceptive stimuli were also altered, however there were no differences in rates of clinically relevant pain. Moderate quality evidence finds the prevalence of clinically relevant pain in patients with schizophrenia is around 35% and clinically relevant headache is around 30%.

February 2022

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Typically, sleep follows a characteristic pattern of four stages, where stage 1 is a state of drowsiness and early sleep, stage 2 comprises the largest component of the sleep cycle and is the first complete loss of awareness of the external environment, stage 3 is a deep slow-wave sleep, and the fourth stage is rapid eye movement (REM) sleep where muscle paralysis and memorable dreaming occurs.

Sleep disturbances include changes in sleep time, sleep latency (the length of time it takes from full wakefulness to sleep) and sleep efficiency (the amount of time spent asleep while in bed). Parasomnias include sleep walking, night terrors, nightmares, sleep paralysis, and dream enactment behaviours. Chronotype describes sleep-wake and activity timing, involving a preference for either evening hours, intermediate (neither) hours, or morning hours. These preferences can change over time and differ in the peaks of circadian rhythms and the secretion of hormones.

What is the evidence for sleep disturbance in people with schizophrenia?

Moderate quality evidence found medium-sized effects of more total sleep time, more time in bed, more evening chronotype, and more motor activity in people with schizophrenia than in controls. There were also small effects of more sleep latency, less sleep efficacy, and more time awake after sleep onset in people with schizophrenia. There were medium-sized effects of increased stage 1 sleep, decreased stage 4 sleep, decreased slow wave sleep, and decreased REM latency. There were small effects of decreased stage 3 sleep and increased REM duration. Sleep disturbances were also found in people at-risk of psychosis compared to controls.

People recently withdrawn from antipsychotics had shorter total sleep time, longer sleep onset latency, decreased sleep efficacy, longer awake time, increased stage 1 sleep, decreased stage 2, 3, and 4 sleep, decreased slow wave sleep and shorter REM latency than controls. People on antipsychotics had significantly longer sleep onset latency, increased stage 2 sleep, and decreased total REM sleep than controls.

Moderate to low quality evidence finds frequent (weekly) nightmares were reported in 9% to 55% of people with schizophrenia. Around 15% reported sleep paralysis and 17% reported sleep-related eating disorders.

February 2022

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Changes in the homeostatic regulation of body temperature can involve increased or decreased body temperature in a neutral environment (baseline temperature), altered response to a temperature stimulus (heat or cold stress), changes to the normal differences between morning and night-time body temperatures (diurnal and circadian variation), variations in the range of typical body temperature changes during the day, and changes to typical differences between core and peripheral body temperatures.

What is the evidence for temperature regulation?

In antipsychotic-free patients, moderate to low quality evidence suggests baseline temperature is reduced, there is less daily variation in temperature, there are differences in variation between peripheral and core temperature, and an altered response to temperature stress when compared to people without schizophrenia.

In mixed groups of antipsychotic-free and medicated patients, moderate to low quality evidence suggests baseline temperature may be increased, circadian rhythms may be altered and there may be increased skin temperature following heat stress stimulus when compared to people without schizophrenia.

February 2022

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