Abstract
Major depression (MDD) has been associated with an altered EEG frontal asymmetry measured in resting state; nevertheless, this association has showed a weak consistency across studies. In the present study, which starts from an evolutionistic view of psychiatric disorders, we investigated frontal asymmetry in MDD, using language as a probe to test the integrity of large inter- and intra-hemispheric networks and processes. Thirty MDD patients (22 women) and 32 matched controls (HC) were recruited for an EEG recording in resting state and during two linguistic tasks, phonological and semantic. Normalized alpha and beta EEG spectral bands were measured across all three conditions in the two groups. EEG alpha amplitude showed no hemispheric asymmetry, regardless of group, both at rest and during linguistic tasks. During resting state, analysis of EEG beta revealed a lack of hemispheric asymmetry in both groups, but during linguistic tasks, HC exhibited the typical greater left frontal beta activation, whereas MDD patients showed a lack of frontal asymmetry and a significantly lower activation of left frontal sites. In depressed patients, positive affect was negatively correlated with depression levels and positively correlated with left frontal EEG beta amplitude. Language represents the human process that requires the largest level of integration between and within the hemispheres; thus, language asymmetry was a valid probe to test the left frontal alteration encompassing highly impairing psychiatric disorders, such as schizophrenia and MDD. Indeed, these severe diseases are marked by delusions, ruminations, thought disorders, and hallucinations, all of which have a clear linguistic or metalinguistic basis.
Highlights
Major depression (MDD) has been associated with an altered EEG frontal asymmetry measured in resting state; this association has showed a weak consistency across studies
As expected for chronic patients, the severity of depressive symptoms measured with clinical scales was, on average, below the cut-off scores of Hamilton Rating Scale for Depression (HAM-D) and BDI-2 inventories (Table 1), confirming a state of remission from acute major depression episodes and a good compliance with pharmacological treatment
Concerning behavioral data, major depressive disorder (MDD) patients showed, during task execution, response times (RTs) similar to those collected from healthy controls, suggesting that drug treatment did not alter patients’ motor skills or response readiness
Summary
Major depression (MDD) has been associated with an altered EEG frontal asymmetry measured in resting state; this association has showed a weak consistency across studies. Language represents the human process that requires the largest level of integration between and within the hemispheres; language asymmetry was a valid probe to test the left frontal alteration encompassing highly impairing psychiatric disorders, such as schizophrenia and MDD These severe diseases are marked by delusions, ruminations, thought disorders, and hallucinations, all of which have a clear linguistic or metalinguistic basis. With respect to the association between cognitive deficit and depression progress, Majer and collaborators[28] found pathological performance in attention and executive tasks at admission, with marginal improvements at discharge; a meta-analysis focused on first-episode MDD patients revealed that cognitive impairments in attention, memory and executive functions are consistently observed since the disease onset[29] Overall, these findings outline that cognitive deficits represent a core feature of depressive disorders[30], related to distinctive patterns of abnormal activity in the frontal regions of the brain[31]. In line with Crow’s hypothesis on the common origin of psychoses, we expected that alteration of language frontal asymmetry may be found in other diseases of the psychiatric triad, such as MDD
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