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A new study reveals pleasant stimuli brings less joy to people with schizophrenia or those who have a risk of psychosis.
People with schizophrenia or those at a risk for psychosis have deviations in the emotional experience—and view pleasant stimuli less positively than someone who does not have schizophrenia nor is prone to psychosis.1
A meta-analysis, which included data from 111 emotion-induced studies and 6913 participants,
looked at several emotional induction studies to explore the emotional experience of people with schizophrenia and prone to psychosis. The analysis was run by Marcel Riehle, PhD, and Tania Lincoln, PhD, both in the department of clinical psychology and psychotherapy at Universität Hamburg, in Germany, as well as Alexandra Straková, of the department of psychology at Comenius University in Bratislava, Slovakia.
The new analysis had 2 goals: to expand on previous meta-analyses and to not just include people with schizophrenia but also those at risk of psychosis.
To accomplish their first goal, Riehle, Straková, and Lincoln studied Cohen and Minor’s seminal meta-analyses which synthesized 26 emotion-induction studies from up to 2008 and compared the emotional experience of those with schizophrenia and not.2 The team explained that emotional induction studies provide the opportunity to compare experimental and control groups for “the same standardized stimuli.”
The study explored negative and positive symptoms. The negative symptoms were associated with a reduced experience of pleasure and increased experience of emotion when presented with a pleasant stimulus.
“The recently posed hypothesis of a schizophrenia spectrum anhedonia paradox points out the peculiarity that people at risk for psychosis appear to show a stronger reduction of their pleasure experience than people with schizophrenia,” the team wrote.
The results showed “no noteworthy emotion in response to pleasant stimuli but moderate elevations of negative emotion in response to pleasant stimuli but moderate elevations of negative emotion in response to pleasant and neutral stimuli in schizophrenia.”
“People with schizophrenia and those at risk for psychosis experienced pleasant stimuli as less positive (small effect) and more negative (moderate effect) than healthy controls,” the investigators continued. “Results were less conclusive for unpleasant stimuli.”
The team carried out the research by searching databases like MEDLINE and PsychINFO on August 16, 2022 for entries dating back from January 1989. They also used Google Scholar to research Cohen and Minor’s studies and pulled relevant studies off the reference lists.
The investigators followed specific criteria when finding studies for their research.
The first criteria: studies must compare people not diagnosed with mental health disorders or not identified with a risk for psychosis with ≥1 experimental population, which could be adults with schizophrenia or at risk for psychosis.
The second criteria: the studies needed “standardized emotionally evocative stimuli to include emotions in a laboratory setting.”
Sensory systems included semantic and behavior, as well as visual and odor.
The team additionally excluded studies in which evocative stimuli could not be categorized into either pleasant, neutral or unpleasant traits, as well as those that were “intensely ambitious or were paired with incongruent or emotion-regulating stimuli or instructions.”
The third criteria said studies must “access the emotional response as a continuous measure (at least 4-point scaling) on at least 1 of 3 types of response scales: unipolar positive emotion, unipolar negative emotion, and bipolar valence.”
Investigators conducted separate meta-analyses for each of the 9 combinations of stimulus categories. They also did moderator analyses, which were performed using meta-regressions with random effect.
The primary outcome analysis found that, with neutral stimuli, individuals with schizophrenia and at a risk for psychosis had significantly higher negative emotions than the healthy controls (people without schizophrenia and a risk for psychosis).
With the unpleasant stimuli, individuals with schizophrenia and those at a risk of psychosis had significantly higher positive and negative emotions.
“In schizophrenia, a larger deficit in positive emotion positive emotion(unipolar) was predicted by higher levels of negative symptoms (z score = −2.98; P = .003) A smaller excess in negative,” investigators wrote.
The investigators ended the report by discussing 4 noteworthy results.
The team first pointed out that that the moderator analyses did not show significant differences between individuals with schizophrenia and those at risk for psychosis. After that, they explained that the inability to experience joy in schizophrenia is unrelated to a lack of the pleasant experience. The team also noted that the studies researched focused mostly on visual stimuli, pushing the other stimulus to the side. Two of 3 of the studies were conducted with visual stimuli.
The meta-analyses exposed a pattern of the abnormal emotional experience of people with schizophrenia, showing how it is already present before the disorder starts.
“In people with schizophrenia with negative symptoms and in at-risk populations, this excess was combined with a deficit in experiencing positive emotion,” investigators concluded. “This depletion of the reward value of normatively pleasant stimuli, therefore, needs to be reconsidered as a potential contributor to motivational impairments, which would make it an important target for prevention and intervention.”