A link between stress and depression: shifts in the balance between the kynurenine and serotonin pathways of tryptophan metabolism and the etiology and pathophysiology of depression

Alteration of tryptophan (TRP) metabolism elicited by proinflammatory cytokines has gained attention as a new concept to explain the etiological and pathophysiological mechanisms of major depression. The kynurenine (KYN) pathway, which is initiated by indoleamine 2,3-dioxygenase (IDO), is the main TRP metabolic pathway. It shares TRP with the serotonin (5-HT) pathway. Proinflammatory cytokines induce IDO under stress, promote the KYN pathway, deprive the 5-HT pathway of TRP, and reduce 5-HT synthesis. The resultant decrease in 5-HT production may relate to the monoamine hypothesis of major depression. Furthermore, metabolites of the KYN pathway have neurotoxic/neuroprotective activities; 3-hydroxykynurenine and quinolinic acid are neurotoxic, whereas kynurenic acid is neuroprotective. The hippocampal atrophy that appears in chronic depression may be associated with imbalances in neurotoxic/neuroprotective activities. Because proinflammatory cytokines also activate the hypothalamo-pituitary-adrenal (HPA) axis, these imbalances may inhibit the hippocampal negative feedback system. Thus, changes in the TRP metabolism may also relate to the HPA axis-hyperactivity hypothesis of major depression. In this article, we review the changes in TRP metabolism by proinflammatory cytokines under stress, which is assumed to be a risk factor for major depression, and the relationship between physiological risk factors for major depression and proinflammatory cytokines.     

Neuromagnetic signals associated with reading a kanji character formed by combining two kanji radicals

To find out which brain regions are responsible for the mental construction and recognition of a kanji character initiated by visually presented kanji radicals, rather than by information retained in the memory, a left hen radical and the corresponding right tsukuri radical were simultaneously presented randomly to either the left or right visual field of seven subjects. Thirty left hen radicals and the corresponding right tsukuri radicals were prepared as stimuli; this combination formed over 500 real or pseudo kanji characters. Instead of their usual left and right positions, the left hen radical was always presented above the right tsukuri radical. As quickly and correctly as possible, the subjects released a key when two kanji radicals constituted a single real kanji character and released another key otherwise. We recorded neuromagnetic responses as well as accuracy and reaction time. Left visual field superiority was observed as regards accuracy. This is in good agreement with previous neuropsychological results. Equivalent current dipoles were localized mainly in the left and/or right occipitotemporal regions (ventral visual pathways), the bilateral occipitoparietal regions (dorsal visual pathways) including the supramarginal region, and the areas surrounding the left superior temporal cortex. We suggest that these regions are related to reading and the mental construction of a kanji character from its radicals.     

Does medial prefrontal cortex activity during self‐knowledge reference reflect the uniqueness of self‐knowledge?1

Abstract: For this study, functional magnetic resonance imaging was used to examine whether medial prefrontal cortex (MPFC) activity during self‐knowledge reference reflects the uniqueness of self‐knowledge. Experiment 1 investigated neural activity during self‐knowledge reference (“Does the word describe you?”) and self‐monitoring (“Does the word make you feel pleasant?”). The results showed that self‐knowledge reference and self‐monitoring activate common neural substrates within the MPFC. Experiment 2 compared neural activity produced by self‐knowledge reference, other‐knowledge (acquaintance‐knowledge) reference (“Does this word describe the person?”), and evaluation (“Is this word socially desirable?”). Results showed no increase in MPFC activity during self‐knowledge reference relative to other‐knowledge reference. Furthermore, self‐knowledge reference and other‐knowledge reference share common neural substrates within the MPFC. The results described indicate that it is unlikely that MPFC activity during self‐knowledge reference reflects the uniqueness of self‐knowledge. The feature, as reflected in MPFC activity, is discussed.     

Illusory temporal order for stimuli at different depth positions

We used four experiments to examine how the perceived temporal order of two visual stimuli depends on the depth position of the stimuli specified by a binocular disparity cue. When two stimuli were presented simultaneously at different depth positions in front of or around a fixation point, the observer perceived the more distant stimulus before the nearer stimulus (Experiments 1 and 2). This illusory temporal order was found only for sudden stimulus presentation (Experiment 3). These results suggest that a common processing, which is triggered by sudden luminance change, underlies this illusion. The strength of the illusion increased with the disparity gradient and the disparity size (Experiment 4). We propose that this illusion has a basis in the processing of motion in depth, which would alert the observer to a potential collision with an object that suddenly emerges in front of the observer.     

认知任务对直立姿势的视觉控制的影响

为揭示认知任务对直立姿势的视觉控制的影响, 本研究采用双重任务的方法, 要求18名健康的成年被试在4种条件(2认知条件×2视觉条件)下尽力保持直立姿势的稳定。姿势动摇的测量采用头顶拍摄的方法并计算误差均方根、平均速度以及Romberg商数。研究结果显示认知任务和视觉条件之间的交互作用显著, 而且当有认知任务时姿势动摇的Romberg商数显著降低。这些结果说明认知任务抑制了直立姿势控制过程中的视觉加工。     

An ERP study on self-relevant object recognition

We performed an event-related potential study to investigate the self-relevance effect in object recognition. Three stimulus categories were prepared: SELF (participant's own objects), FAMILIAR (disposable and public objects, defined as objects with less-self-relevant familiarity), and UNFAMILIAR (others' objects). The participants' task was to watch the stimuli passively. Results showed that left-lateralized N250 activity differentiated SELF and FAMILIAR from UNFAMILIAR, but SELF and FAMILIAR were not differentiated. In the later time-course, SELF was dissociated from FAMILIAR, indicating the self-relevance effect in object recognition at this stage. This activity did not show consistent lateralization, in contrast to previous studies reporting right lateralization in self-relevant face and name recognition. We concluded that in object recognition, self-relevance was processed by higher-order cognitive functions later than 300ms after stimulus onset.     

Roots of smile: a preterm neonates' study

Twenty-two preterm neonates were observed 1 h per neonate in the NICU. Ninety-five spontaneous smiles were recorded. Younger and smaller neonates showed more and longer spontaneous smiles than older and larger. The youngest neonate was 200 days from conception on the observational day. She was 511 g. This infant showed spontaneous smiles. The roots of spontaneous smiles are discussed.     

The Effect of Pink/Blue Clothing on Implicit and Explicit Gender‐Related Self‐Cognition and Attitudes Among Men

In many cultures worldwide, one stereotype emerges: Pink is associated with girls and blue is associated with boys. Based on the enclothed cognition theory, the present study examined the effects of men's pink clothing on gender‐related self‐cognition and sex‐role attitudes. Male Japanese participants wore either a pink or blue coat and completed a gender stereotype Implicit Association Test, a self‐rating scale, and gender attitude scales (a measure of egalitarian sex‐role attitude and the Ambivalent Sexism Inventory). Results showed that among participants with low self‐esteem, the implicit self–feminine association was stronger in the pink condition than in the blue condition. On the other hand, participants with high self‐esteem explicitly associated themselves more with power‐oriented traits compared with interpersonal‐oriented traits when they wore a pink coat compared with those who wore a blue coat. Additionally, participants in the pink condition expressed stronger egalitarian sex‐role attitudes and weaker benevolent sexism than those in the blue condition. We propose that men's pink clothing is a means of diminishing gender stereotypes and traditional sex‐role attitudes.     

Fos expression in CRF-containing neurons in the rat paraventricular nucleus after central administration of neuromedin U

We examined the effects of centrally administered neuromedin U (NMU) on corticotrophin-releasing factor (CRF)-containing neurons in the hypothalamic paraventricular nucleus (PVN) of rats, using double immunohistochemistry for CRF and Fos. Almost all CRF-containing neurons in the parvocellular divisions of the PVN expressed Fos-like immunoreactivity 90 min after intracerebroventricular administration of NMU (3 nmol/rat). This results suggest the possibility that central NMU may be involved in stress-induced activation of CRF-containing neurons in the PVN.     

Affective integration speeds trait processing

We investigated whether affective integration increases the speed of processing of personality trait knowledge. The fan effect was compared between cases where trait knowledge is stored with the affective value and cases where it is not stored with the affective value. 18 college students first memorized a set of traits about fictitious individuals and then made recognition judgments. In the 2 x 2 factorial repeated-measures design, the number of traits learned about a fictitious individual and whether those traits were integrated by a shared affective value were manipulated. The significant interaction showed that knowledge of personality trait with affective integration was processed quickly even if the particular person's memory had rich connections with traits.