RESUMO
BACKGROUND: So far findings on emotional face processing among depressed individuals reveal an inconsistent image, with only some studies supporting a mood-congruent bias in salience processing. Thereby, many results are based on the processing of sad emotions and mostly focused on resting-state connectivity analysis. The present study aimed to target this misbalance by implementing a social oddball paradigm, with a special focus on the amygdala, the ACC, the insula and subdivisions of insula and ACC. METHODS: Twenty-seven depressed patients and twenty-seven non-depressed controls took part in a fMRI event-related social oddball paradigm based on smiling facial expressions as target stimuli embedded in a stream of neutral facial expressions. FMRI activation and functional connectivity analysis were calculated for the pre-defined ROIs of the salience network (SN), with a special focus on twelve insular subdivisions and six ACC subdivisions. RESULTS: For both groups the social oddball paradigm triggered similar BOLD responses within the pre-defined ROIs, while the quality of functional connectivity showed pronounced alterations from the salience network to the ventral attention- and default mode network (DMN). CONCLUSION: On a first level of target detection, smiling faces are equally processed and trigger similar bold responses in structures of the salience network. On a second level of inter-network communication the brain of depressed participants tends to be pre-formed for self-referential processing and rumination instead of fast goal directed behavior and socio-emotional cognitive processing.
Assuntos
Transtorno Depressivo Maior , Reconhecimento Facial , Córtex Cerebral , Transtorno Depressivo Maior/diagnóstico por imagem , Expressão Facial , Humanos , Imageamento por Ressonância MagnéticaRESUMO
INTRO: The human sense of smell is highly individual and characterized by a strong variability in the perception and evaluation of olfactory stimuli, depending on cultural imprint and current physiological conditions. Since this individual perspective has often been neglected in fMRI studies on olfactory hedonic coding, this study focuses on the neuronal activity and connectivity patterns resulting from subject-specific olfactory stimulation. METHODS: Thirty-one normosmic participants took part in a fMRI block designed paradigm consisting of three olfactory stimulation sessions. The most pleasant and unpleasant odors were individually specified during a pre-test for each participant and validated in the main experiment. Mean activation and functional connectivity analysis focusing on the right and left piriform cortex were performed for the predefined olfactory regions-of-interest (ROIs) and compared between the three olfactory conditions. RESULTS: Individual unpleasant olfactory stimulation as compared to pleasant or neutral did not alter mean BOLD activation in the predefined olfactory ROIs but led to a change in connectivity pattern in the right piriform cortex. CONCLUSION: Our data suggests that the individual pleasantness of odors is not detectable by average BOLD magnitude changes in primary or secondary olfactory brain areas, but reflected in temporal patterns of joint activation that create a network between the right piriform cortex, the left insular cortex, the orbitofrontal cortex, and the precentral gyrus. This network may serve the evolutionary defense mechanism of olfaction by preparing goal-directed action.
Assuntos
Encéfalo/fisiologia , Individualidade , Imageamento por Ressonância Magnética/métodos , Rede Nervosa/fisiologia , Odorantes , Percepção Olfatória/fisiologia , Adolescente , Adulto , Encéfalo/diagnóstico por imagem , Feminino , Humanos , Masculino , Rede Nervosa/diagnóstico por imagem , Consumo de Oxigênio/fisiologia , Adulto JovemRESUMO
The insular cortex plays a key role in the integration of multimodal information and in interoceptive and exteroceptive processing. For instance, neurons in the central dorsal insula that are active during interoceptive tasks, also show an adaptation to gustatory stimulation. We tested the link between interoception and exteroception for the olfactory system (i.e., the second domain of chemosensation). In a sample of 31 participants, olfactory function was assessed in a two dimensional approach while the Heartbeat Perception Task served as a measurement for cardiac interoceptive accuracy. Subsequent fMRI sessions were performed on a 3-Tesla MR scanner containing 12-15 olfactory stimulation trials with a mildly pleasant food-related odor (coffee). Persons scoring high in the cardiac interoceptive accuracy task presented stronger smelling abilities as well as enhanced BOLD responses following olfactory stimulation. The olfactory stimulation triggered enhanced insular activation patterns in the central dorsal insular cortex. Consistent with prior findings on the coherence of gustatory and interoceptive processing in the central dorsal insula, these results base the insula as a common region for the integration of interoception and exteroception. We propose an explanatory model of how exteroception triggers the integration of intero- and exteroceptive sensations in the central dorsal insular cortex.