Suicide is a major public health problem, with over 700,000 people dying by suicide every year globally.
Identifying factors that may indicate risk for suicidal thoughts and behaviors is an important area of research, as this could aid prevention and intervention efforts.
Some studies have investigated whether asymmetric brain activity, as measured by electroencephalography (EEG), might serve as a biomarker for suicide risk.
However, research findings have been mixed.
A new comprehensive review and meta-analysis aimed to provide clarity on what the overall body of research shows regarding associations between EEG asymmetry and suicidality.
Key Facts:
- The meta-analysis included 13 studies with a total of 1,307 participants. The studies were conducted worldwide, including the U.S., South Korea, Europe, and elsewhere.
- The studies measured EEG asymmetry, referring to differences in electrical brain activity between the left versus right hemispheres.
- Suicidality was assessed using measures of suicidal ideation, past suicide attempts, or clinician interviews. Around half of the studies focused on participants with major depressive disorder.
- Overall, the meta-analysis found no significant link between EEG asymmetry and suicidality. Findings were inconsistent across studies.
Source: Clin Psychopharmacol Neurosci.
EEG Asymmetry & Suicidality: A Complex Topic Requiring More Research
The idea for investigating EEG asymmetry as a suicide biomarker comes from research showing asymmetric brain activity is linked to mental health problems like depression and anxiety.
Specifically, greater activity in the right versus left hemisphere has been associated with negative emotionality and withdrawal behaviors characteristic of internalizing disorders.
Given the withdrawal and pessimism associated with right EEG asymmetry, researchers have hypothesized this pattern may also relate to suicidal ideation and behavior.
However, the comprehensive meta-analysis indicates EEG asymmetry does not appear to be systematically connected to suicidality based on research so far.
The authors conclude that EEG asymmetry may not be a reliable biomarker for suicide risk, but more research is still needed.
They note a number of limitations in the existing literature that preclude definitive conclusions:
- Small sample sizes in many studies
- Differences in how EEG data was collected (e.g. eyes open vs. closed)
- No standard suicide assessment tool used across studies
- Excluding participants with conditions like bipolar disorder that impact EEG
- Not accounting for comorbid mental health symptoms
While findings were null overall, the review also highlights new research directions that show promise, like analyzing EEG during cognitive tasks and examining brain activity patterns unique to suicide attempters versus those with only suicidal thoughts.
The Complex Link Between Brain Activity and Suicide
The human brain contains billions of interconnected neurons that communicate through electrical and chemical signals.
EEG can measure asymmetric patterns in the brain’s electrical activity.
But why would asymmetric brain activity relate to something as complex as suicidal thoughts and behaviors in the first place?
Research suggests the left and right brain hemispheres take on some different roles.
The left hemisphere is more involved with logical thinking and positive emotions, while the right hemisphere specializes more in negative emotions, withdrawal, and analytical thinking.
However, psychology experts emphasize suicide has a wide range of causes.
Both environmental influences and genetic factors play a role.
Therefore, it is unlikely that any single brain measurement could serve as a clear-cut biomarker for suicide risk.
That said, EEG asymmetry and other brain imaging techniques may still provide insight on biological factors that interact with life experiences to confer suicide risk.
The brain does not operate in isolation when it comes to mental health.
For example, stressful events like trauma could potentially cause changes in brain activity over time that increase suicide risk.
Or certain asymmetric brain patterns measured by EEG could reflect underlying vulnerabilities that get activated in the presence of major stressors.
The interplay between environmental and biological factors highlights why more research on EEG, genetics, neurotransmitters, and other potential biological contributors is warranted.
A Focus on Resting State Brain Activity
Most of the 13 studies included in the meta-analysis looked at resting state EEG asymmetry.
This means participants’ brain activity was measured when they were calm and still, not engaged in a specific task.
Recording resting state EEG can provide insight on intrinsic patterns of brain activation.
This method has been used in past studies linking EEG asymmetry to mental health issues like anxiety and depression.
Participants sat quietly for around 2 to 7 minutes while EEG data was collected, sometimes with their eyes open and sometimes with eyes closed.
The studies then compared EEG asymmetry values between suicidal versus non-suicidal groups.
Overall, no clear differences emerged, suggesting resting EEG asymmetry is likely not a useful biomarker for suicidality on its own.
However, one study that assessed EEG during cognitive tasks found differences between suicide attempters and non-attempters.
More research on brain activation patterns during cognitive or emotional tasks could reveal suicide risk markers not apparent at resting state.
Heterogeneity in Research Methods
A major limitation highlighted by the review authors is inconsistency in measurement methods across the studies investigating links between EEG asymmetry and suicide risk.
For example, there was variability in:
- Duration of EEG recording (from 2 to 7 minutes)
- EEG acquisition conditions – eyes open vs. closed
- Electrodes used to calculate asymmetry
- Methods used to quantify asymmetry
- Measures used to assess suicidal thoughts and behaviors
This heterogeneity likely contributed to the lack of clear conclusions that could be drawn from the research so far.
Moving forward, the field would benefit from greater standardization in how EEG and suicidality are measured across studies.
This could allow for more robust comparisons and conclusions regarding whether EEG asymmetry relates to suicide risk.
Possible Publication Bias
The authors speculate the lack of clear findings may also stem in part from publication bias.
Specifically, studies finding no link between EEG asymmetry and suicide may be less likely to get published than studies showing an association.
Indeed, visual inspection of a funnel plot indicated some potential publication bias, with an absence of smaller studies showing null results.
Unpublished studies finding no differences in EEG asymmetry between suicidal and non-suicidal groups could change the overall conclusions.
This highlights the need for researchers to report both significant and null findings to provide a complete picture of what the evidence does or does not show.
As is, potential publication bias limits the strength of conclusions that can be drawn from the available published research.
The Need for Bigger Samples
Another limitation noted involves the small sample sizes included in most of the reviewed studies.
The largest study provided 40% of the total participants, while the remaining studies had relatively few participants.
Small samples increase the likelihood that any significant effects are due to chance.
Larger scale studies are needed to reliably detect subtle EEG asymmetry differences that may exist between suicidal and non-suicidal groups.
Pooling data across multiple research groups could help overcome the challenges of recruiting enough suicidal participants for adequately powered EEG studies.
Multi-site collaborations and data sharing efforts will advance knowledge in this area.
Accounting for Comorbid Mental Health Conditions
Up to 90% of people who die by suicide experience mental health issues like depression, anxiety, and substance abuse.
Therefore, suicidality often co-occurs with other psychiatric symptoms that may also relate to asymmetric brain activity in their own right.
This makes it hard to isolate the specific effects of suicidal thoughts versus other symptoms.
Some studies excluded participants with certain diagnoses like bipolar disorder that impact EEG.
But this precludes generalizing findings to a key segment of the suicidal population.
Ideally, future studies will measure and control for comorbid symptoms rather than excluding participants.
Analyzing subgroups of participants with varying symptom profiles could also help clarify the unique impact of suicidality on brain activity.
A Starting Point for Further Research
In summary, the comprehensive literature review and meta-analysis provides an indispensable starting point for this emerging area of research.
The findings to date indicate EEG asymmetry is unlikely a clear-cut diagnostic biomarker for suicide risk.
However, the authors identify promising future directions such as analyzing brain activity during cognitive tasks, looking at specific event-related brain potential patterns, and studying differences between suicidal ideators versus attempters.
The lack of consistent standardization in measurement methods also underscores the need for consensus on optimal data collection procedures in future EEG and suicide research.
With improved methodology and measurement along with larger-scale studies, there is still much potential for better understanding the neurobiology underlying suicidal thoughts and behaviors.
Although the existing research does not show EEG asymmetry is a suicide risk biomarker, investigators are only just scratching the surface when it comes to the neuroscience of suicide.
Human behavior and mental health have complex neurobiological underpinnings that will require looking beyond any single brain measurement technique.
A holistic perspective accounting for both biological and environmental influences will be critical for advancing knowledge on the tragic and devastating public health issue of suicide.
References
- Study: The link between suicidality and EEG asymmetry
- Authors: Laine B. Butler & Kate B. Nooner (2023)
