Fractal geometry has recently been proposed as a useful tool for characterizing the complexity of the brain cortex, which is likely to derive from the recurrence of sulci–gyri convolution patterns. The index used to describe the cortical complexity is called fractal dimensional (FD) and was employed by different research exploring the neurobiological correlates of distinct pathological and nonpathological conditions. This review aims to describe the literature on the application of this index, summarize the heterogeneities between studies and inform future research on this topic. Sixty‐two studies were included in the systematic review. The main research lines concern neurodevelopment, aging and the neurobiology of specific psychiatric and neurological disorders. Overall, the included papers indicate that cortical complexity is likely to reduce during aging and in various pathological processes affecting the brain. Nevertheless, the high heterogeneity between studies strongly prevents the possibility of drawing conclusions. Further research considering this index besides other morphological values is needed to better clarify the role of FD in characterizing the cortical structure.

Objective: Suicide is a leading cause of death worldwide. Identifying factors associated with suicidality (suicidal ideation [SI]/suicidal behavior) could increase our understanding of the pathophysiological underpinnings of suicide and improve its prevention.Methods: We conducted a systematic review (PubMed/PsycInfo/Cochrane databases, up to September 2020) and random‐effect meta‐analysis including observational studies comparing peripheral C‐reactive protein (CRP) levels in suicidal versus non‐suicidal patients affected by any psychiatric disorder and healthy controls (HC). Primary outcome was the CRP standardized mean difference (SMD) between patients with high suicidality versus those with absent or low suicidality. Secondary outcomes were SMD of CRP levels between those with suicide attempt versus no suicide attempt, as well as between those with (high) versus low or absent SI. Quality of included studies was measured with Newcastle‐Ottawa scale.Results: Out of initial 550 references, 21 observational studies involving 7682 subjects (7445 with mood disorders or first‐episode psychosis, 237 HC) were included. A significant association of CRP levels with suicidality (SMD 0.688, 95% CI 0.476–0.9, p < 0.001) emerged. CRP levels were higher in individuals with high SI (SMD 1.145, 95% CI 0.273–2.018, p = 0.010) and in those with suicide attempt (SMD 0.549, 95%CI 0.363–0.735, p < 0.001) than non‐suicidal individuals (either patients or HC). Main analyses were confirmed in sensitivity analysis (removing HC), and after adjusting for publication bias. The cross‐sectional design of included studies, and the high heterogeneity of diagnosis and treatment limit the generalizability of these results. Median quality of included studies was high.Conclusion: CRP is associated with higher suicidality in patients with mental disorders. Large cohort studies longitudinally monitoring CRP levels are needed to explore its longitudinal association with suicidality.

Background: Every year, more than 800,000 people die by suicide, three‐quarters of which are males. Economic factors influence suicide rates, but a worldwide perspective of their impact according to age and sex is lacking.Method: We queried publicly available datasets on economic factors and on suicide rates stratified according to sex and age, from 1991 to 2017, for 175 countries. Thus, we analyzed approximately 21 million deaths by suicide using a multivariable regression model approach.Results: Every 1% increase in global unemployment rates is associated with a 1% upsurge in male deaths by suicide (Relative risk (RR) = 1.01 [CI 95% 1.00–1.01] with respect to females) or 5000 excess male deaths. A 1% higher unemployment rate also exerts age‐specific effects on suicide rates, since, among adults aged 30–59, the suicide rate is increased by 2–3%. Lastly, for every 1000 US dollar increase in the GDP per capita, suicide rates are reduced by 2% (RR = 0.98 [0.98–0.98]), corresponding to a reduction of 14,000–15,000 suicide deaths per year globally.Conclusions: Males who have lost their jobs in adulthood are those at higher risk of suicide and to whom financial support measures should be delivered in a timely manner.