A Neural Basis for the Acquired Capability for Suicide

Abstract

The high rate of fatal suicidal behavior (SB) in men is an urgent issue as highlighted in the public eye via news sources and media outlets. In this study, we have attempted to address this issue and understand the neural substrates underlying the gender differences in the rate of fatal SB. The Interpersonal-Psychological Theory of Suicide has proposed an explanation for the seemingly paradoxical relationship between gender and SB, i.e., greater non-fatal suicide attempts by women but higher number of deaths by suicide in men. This theory states that possessing suicidal desire (due to conditions such as depression) alone is not sufficient for a lethal suicide attempt. It is imperative for an individual to have the acquired capability for suicide (ACS) along with suicidal desire in order to die by suicide. Therefore, higher levels of ACS in men may explain why men are more likely to die by suicide than women, despite being less likely to experience suicidal ideation or depression. In this study, we used activation likelihood estimation meta-analysis to investigate a potential ACS network that involves neural substrates underlying emotional stoicism, sensation-seeking, pain tolerance, and fearlessness of death, along with a potential depression network that involves neural substrates that underlie clinical depression. Brain regions commonly found in ACS and depression networks for males and females were further used as seeds to obtain regions functionally and structurally connected to them. We found that the male-specific networks were more widespread and diverse than the female-specific ones. Also, while the former involved motor regions, such as the premotor cortex and cerebellum, the latter was dominated by limbic regions. This may support the fact that suicidal desire generally leads to fatal/decisive action in males, while, in females, it manifests as depression, ideation, and generally non-fatal actions. The proposed model is a first attempt to characterize the neural networks underlying gender differences in SB. Future studies should examine the proposed network to better characterize and refine this network using tasks specifically targeted toward constructs underlying ACS.

Keywords: depression; diffusion tensor imaging; functional magnetic resonance imaging; gender difference; meta-analysis; meta-analytic functional connectivity; structural connectivity; suicide.

Figure 1

A schematic illustration of the entire procedure involving ALE meta-analysis, meta-analytic functional connectivity modeling, and structural connectivity analysis.

Figure 2

The ACS network for males (A) and females (B). The color bar illustrates the color scheme used for depicting the regions that were commonly activated by just one, two, three, or four of the following conditions – emotion, pain processing, sensation-seeking, and fear. Voxels activated by any one of the above mentioned four conditions are shown in blue, by any two of the above conditions are shown in aquamarine, and by any three of the four conditions in yellow, respectively. Regions represented by aquamarine and yellow colors together form the ACS network.

Figure 3

The depression network for males (A) and females (B).

Figure 4

(A) ACS and depression networks identified in males, both overlaid on same anatomical image. (B) ACS and depression networks identified in females, both overlaid on same anatomical image. (C) Voxels commonly found in the ACS and depression networks identified in males and females, overlaid on a single anatomical image. These form the ACS–depression network seeds.

Figure 5

ACS–depression network in males (A) and females (B) obtained by finding voxels coactivated by the ACS–depression network seeds found in Figure 4.

Figure 5

ACS–depression network in males (A) and females (B) obtained by finding voxels coactivated by the ACS–depression network seeds found in Figure 4.

Figure 6

ACS–depression network, which was obtained separately in males and females, is overlaid on a single anatomical image. Green represents the ACS–depression network in females, red in males, and yellow represents their overlap. Only regions of overlap are labeled in the figure while Table 5 provides labels of regions, which were exclusively coactivated with ACS–depression network seeds only in males and females.

Figure 7

The axonal trajectories derived from the ACS–depression network seeds defined by coactivated voxels from ACS and Depression networks in males (A) as well as females (B). The four panels in (A,B) are the different views of the same figure. (A) Yellow – fibers from right thalamus, green – fibers from left precentral gyrus, dark blue – fibers from right caudate, purple – fibers from right cingulate gyrus, light blue – fibers from right insula, pink – fibers from right mid frontal gyrus, red – fibers from right putamen, orange – fibers from left putamen, claustrum, caudate. (B) Red – fibers from right putamen, green – fibers from left insula, blue – fibers from left putamen (hidden inside the green fibers from left insula, so not seen in the figures), purple – fibers from left globus pallidus.

Figure 8

Fibers from seeds in left and right putamen in males and females both overlaid on a single anatomical. Red – fibers in males, green – fibers in females. Both panels represent different views of the same figure.