Post by Kayla Simanek
What's the science?
While society may view suicide attempts as strategic, from a clinical standpoint, suicidal behavior is often attributed to impaired decision-making in moments of crisis. One possibility may be that suicidal individuals do not optimally incorporate transient experience with long-term values, goals, and prior knowledge. However, this hypothesis may oversimplify the complexity of decision-making during crises. Two more specific factors related to learning that may contribute to a suicide attempt are: 1) poor integration of recent experience with prior experience and learned values (i.e. disrupted learning of expected values) and 2) an impaired ability to compare the worth or value of two options and (i.e. compare learned values when faced with choice). This week in Biological Psychiatry, Dombrovski and colleagues tested these two hypotheses to distinguish between the roles of value learning and value comparison in people with histories of suicide attempts.
How did they do it?
The authors conducted a three-choice decision making task. Across 300 trials in the task, participants picked from three pictures on a screen (each of which had a different probability of being the ‘correct’ picture over a series of trials) and were rewarded a small amount of money for picking the correct picture. 260 adults participated in the study and were separated into four groups: major depression with suicide attempts, major depression with suicidal thoughts, non-suicidal depression or healthy (non-depressed). Groups were further stratified by lethality of previous suicide attempts to assess the correlation between attempt severity and task performance. Learning during the task was analyzed by a participant’s responsiveness to reinforcement (monetary compensation). The time taken to decide between three choices was measured as a reflection of the participant’s ability to learn from feedback. Participants’ ability to differentiate between values was also measured by response time: choices close in value would theoretically increase the time taken to decide. Finally, analysis of decision trends within groups was conducted. The authors looked at whether each group chose the best or second-best option (exploitative choices) or a third, obscure option (exploratory choice) most regularly to determine difference in choice preference between groups.
What did they find?
The authors found that those who had attempted suicide were less responsive to reinforcement compared to other groups. Additionally, rewarding feedback slowed the decision time of suicide attempters more than non-attempters or those with suicidal thoughts. Participants with attempts considered to be highly lethal were even less responsive to reinforcement and made slower decisions compared to those participants with less lethal suicide attempts. This data suggests that participants with suicide attempts have difficulty learning worth based on outcomes (supports hypothesis #1). Suicide attempters’ decision time was also slowed by choices with subtle differences in value (probability of being the correct choice), suggesting that these participants have trouble distinguishing between closely ranked values. This conclusion supports hypothesis 2 and could explain the over-estimation of the value of suicide in times of crisis. Finally, analysis of answer choice frequency within groups revealed that suicide attempters more often chose exploitative options whereas non-attempters more often chose the exploratory option. This suggests that the suicidal individual’s ability to search for and consider alternative options is impaired.
What's the impact?
This is the first study to compare the contribution of learning expected value and comparison of learned value in depressed suicide attempters. This study found that both learning via reinforcement and value comparison are more impaired in individuals with major depression and a history of suicidal behavior than those without. This understanding may help shape treatment of suicidal individuals and prevent lethal outcomes in times of crisis.
Dombrovski et al. Value-based choice, contingency learning and suicidal behavior in mid-life and late-life depression. Biological Psychiatry (2018). Access the original scientific publication here.