Disgust evoked by strong wormwood bitterness influences the processing of visual food cues in women: An ERP study.

The perception of intense bitterness is associated with disgust and food rejection. The present cross-modal event-related potential (ERP) study investigated whether a bitter aftertaste is able to influence affective ratings and the neuronal processing of visual food cues. We presented 39 healthy normal-weight women (mean age: 22.5 years) with images depicting high-caloric meat dishes, high-caloric sweets, and low-caloric vegetables after they had either rinsed their mouth with wormwood tea (bitter group; n = 20) or water (control group; n = 19) for 30s. The bitter aftertaste of wormwood enhanced fronto-central early potentials (N100, N200) and reduced P300 amplitudes for all food types (meat, sweets, vegetables). Moreover, meat and sweets elicited higher fronto-central LPPs than vegetables in the water group. This differentiation was absent in the bitter group, which gave lower arousal ratings for the high-caloric food. We found that a minor intervention ('bitter rinse') was sufficient to induce changes in the neuronal processing of food images reflecting increased early attention (N100, N200) as well as reduced affective value (P300, LPP). Future studies should investigate whether this intervention is able to influence eating behavior.

The role of left inferior frontal cortex during audiovisual speech perception in infants.

In the first year of life, infants' speech perception attunes to their native language. While the behavioral changes associated with native language attunement are fairly well mapped, the underlying mechanisms and neural processes are still only poorly understood. Using fNIRS and eye tracking, the current study investigated 6-month-old infants' processing of audiovisual speech that contained matching or mismatching auditory and visual speech cues. Our results revealed that infants' speech-sensitive brain responses in inferior frontal brain regions were lateralized to the left hemisphere. Critically, our results further revealed that speech-sensitive left inferior frontal regions showed enhanced responses to matching when compared to mismatching audiovisual speech, and that infants with a preference to look at the speaker's mouth showed an enhanced left inferior frontal response to speech compared to infants with a preference to look at the speaker's eyes. These results suggest that left inferior frontal regions play a crucial role in associating information from different modalities during native language attunement, fostering the formation of multimodal phonological categories.

Cortisol awakening response and cognitive performance in hypertensive and normotensive older people.

Healthy older people with a cortisol awakening response (CAR) of decreased magnitude show worse frontal cortex-related cognitive performance. Systemic hypertension has been related to a CAR of decreased magnitude. Additionally, worse executive function and processing speed have been observed in older people with systemic hypertension. This is the first study to examine the relationship between the CAR (measured with six saliva samples at home on two consecutive weekdays) and cognitive performance, in both hypertensive (n=26) and normotensive (n=28) older people (from 56 to 78years old). Hypertensive participants showed lower morning cortisol secretion, and they also woke up earlier. No differences in CAR were observed. A CAR of decreased magnitude was related to worse executive function in both hypertensive and normotensive participants, but to slower processing speed only in normotensive participants. Being treated with antihypertensive for a longer period of time was related to a CAR of increased magnitude and better performance on executive function. Our findings suggest that earlier awakening time in hypertensive older people might underlie the lower overall morning cortisol secretion observed in previous studies. Additionally, this study confirms that a dysregulation of the CAR is related to worse executive function, and it extends this association to hypertensive older people. Finally, it is worth noting that hypertension may moderate the relationship between CAR and processing speed.

The representation of oral fat texture in the human somatosensory cortex.

How fat is sensed in the mouth and represented in the brain is important in relation to the pleasantness of food, appetite control, and the design of foods that reproduce the mouthfeel of fat yet have low energy content. We show that the human somatosensory cortex (SSC) is involved in oral fat processing via functional coupling to the orbitofrontal cortex (OFC), where the pleasantness of fat texture is represented. Using functional MRI, we found that activity in SSC was more strongly correlated with the OFC during the consumption of a high fat food with a pleasant (vanilla) flavor compared to a low fat food with the same flavor. This effect was not found in control analyses using high fat foods with a less pleasant flavor or pleasant-flavored low fat foods. SSC activity correlated with subjective ratings of fattiness, but not of texture pleasantness or flavor pleasantness, indicating a representation that is not involved in hedonic processing per se. Across subjects, the magnitude of OFC-SSC coupling explained inter-individual variation in texture pleasantness evaluations. These findings extend known SSC functions to a specific role in the processing of pleasant-flavored oral fat, and identify a neural mechanism potentially important in appetite, overeating, and obesity.

Inversion effects in face-selective cortex with combinations of face parts.

The face inversion effect has been used as a basis for claims about the specialization of face-related perceptual and neural processes. One of these claims is that the fusiform face area (FFA) is the site of face-specific feature-based and/or configural/holistic processes that are responsible for producing the face inversion effect. However, the studies on which these claims were based almost exclusively used stimulus manipulations of whole faces. Here, we tested inversion effects using single, discrete features and combinations of multiple discrete features, in addition to whole faces, using both behavioral and fMRI measurements. In agreement with previous studies, we found behavioral inversion effects with whole faces and no inversion effects with a single eye stimulus or the two eyes in combination. However, we also found behavioral inversion effects with feature combination stimuli that included features in the top and bottom halves (eyes-mouth and eyes-nose-mouth). Activation in the FFA showed an inversion effect for the whole-face stimulus only, which did not match the behavioral pattern. Instead, a pattern of activation consistent with the behavior was found in the bilateral inferior frontal gyrus, which is a component of the extended face-preferring network. The results appear inconsistent with claims that the FFA is the site of face-specific feature-based and/or configural/holistic processes that are responsible for producing the face inversion effect. They are more consistent with claims that the FFA shows a stimulus preference for whole upright faces.

Effects of category learning on neural sensitivity to non-native phonetic categories.

Categorical perception, an increased sensitivity to between- compared with within-category contrasts, is a stable property of native speech perception that emerges as language matures. Although recent research suggests that categorical responses to speech sounds can be found in left prefrontal as well as temporo-parietal areas, it is unclear how the neural system develops heightened sensitivity to between-category contrasts. In the current study, two groups of adult participants were trained to categorize speech sounds taken from a dental/retroflex/velar continuum according to two different boundary locations. Behavioral results suggest that for successful learners, categorization training led to increased discrimination accuracy for between-category contrasts with no concomitant increase for within-category contrasts. Neural responses to the learned category schemes were measured using a short-interval habituation design during fMRI scanning. Whereas both inferior frontal and temporal regions showed sensitivity to phonetic contrasts sampled from the continuum, only the bilateral middle frontal gyri exhibited a pattern consistent with encoding of the learned category scheme. Taken together, these results support a view in which top-down information about category membership may reshape perceptual sensitivities via attention or executive mechanisms in the frontal lobes.

What is right-hemisphere contribution to phonological, lexico-semantic, and sentence processing? Insights from a meta-analysis.

To evaluate the relative role of left and right hemispheres (RH) and describe the functional anatomy of RH during ortholinguistic tasks, we re-analyzed the 128 papers of a former left-hemisphere (LH) meta-analysis (Vigneau et al., 2006). Of these, 59 articles reported RH participation, providing 105 RH language contrasts including 218 peaks compared to 728 on the left, a proportion reflecting the LH language dominance. To describe inter-hemispheric interactions, in each of the language contrasts involving both hemispheres, we distinguished between unilateral and bilateral peaks, i.e. having homotopic activation in the LH in the same contrast. We also calculated the proportion of bilateral peaks in the LH. While the majority of LH peaks were unilateral (79%), a reversed pattern was observed in the RH; this demonstrates that, in contrast to the LH, the RH works in an inter-hemispheric manner. To analyze the regional pattern of RH participation, these unilateral and bilateral peaks were spatially clustered for each language component. Most RH phonological clusters corresponded to bilateral recruitment of auditory and motor cortices. Notably, the motor representation of the mouth and phonological working memory areas were exclusively left-lateralized, supporting the idea that the RH does not host phonological representations. Right frontal participation was not specific for the language component involved and appeared related to the recruitment of attentional and working memory areas. The fact that RH participation during lexico-semantic tasks was limited to these executive activations is compatible with the hypothesis that active inhibition is exerted from the LH during the processing of meaning. Only during sentence/text processing tasks a specific unilateral RH-temporal involvement was noted, likely related to context processing. These results are consistent with split-brain studies that found that the RH has a limited lexicon, with no phonological abilities but active involvement in the processing of context.

Regulated and unregulated forms of cortisol reactivity: a dual vulnerability model.

OBJECTIVE: To test in a laboratory setting the hypothesis that the most problematic daily outcomes should be particular to individuals displaying higher cortisol reactivity and deficits in executive functioning as assessed in a task-switching paradigm. METHODS: Thirty-eight volunteers completed a comprehensive assessment protocol. Individual differences in cortisol reactivity were quantified in an initial laboratory session involving a social stress speech task. Subsequently, individual differences in task-switching costs in a cognitive paradigm were assessed in a second session. Participants then reported on four problematic outcomes-error reactivity; worry; core aspects of negative emotionality; and aggression behavior frequency-for 15 consecutive days. RESULTS: Levels of cortisol reactivity did not predict task-switching costs. Instead, and as hypothesized, individual differences in cortisol reactivity and task-switching costs interacted to predict the problematic daily outcomes. The highest levels of such problematic outcomes were particular to high cortisol reactors also exhibiting greater task-switching costs. CONCLUSIONS: The findings support the dual vulnerability model proposed and are discussed from temperamental, health risk, and daily outcome perspectives. These findings indicate that cortisol is a risk factor, particularly when combined with deficiencies in task-switching.

Neural mechanisms of the testosterone-aggression relation: the role of orbitofrontal cortex.

Testosterone plays a role in aggressive behavior, but the mechanisms remain unclear. The present study tested the hypothesis that testosterone influences aggression through the OFC, a region implicated in self-regulation and impulse control. In a decision-making paradigm in which people chose between aggression and monetary reward (the ultimatum game), testosterone was associated with increased aggression following social provocation (rejecting unfair offers). The effect of testosterone on aggression was explained by reduced activity in the medial OFC. The findings suggest that testosterone increases the propensity toward aggression because of reduced activation of the neural circuitry of impulse control and self-regulation.

Perceived mental effort correlates with changes in tonic arousal during attentional tasks.

BACKGROUND: It has been suggested that perceived mental effort reflects changes in arousal during tasks of attention. Such changes in arousal may be tonic or phasic, and may be mediated by the locus-coeruleus norepinephrine (LC-NE) system. We hypothesized that perceived mental effort during attentional tasks would correlate with tonic changes in cortical arousal, as assessed by relative electroencephalogram (EEG) band power and theta/beta ratio, and not with phasic changes in cortical arousal, assessed by P300 amplitude and latency. METHODS: Forty-six healthy individuals completed tasks that engage the anterior and posterior attention networks (continuous performance task, go/no-go task, and cued target detection task). During completion of the three attentional tasks a continuous record of tonic and phasic arousal was taken. Cortical measures of arousal included frequency band power, theta/beta ratios over frontal and parietal cortices, and P300 amplitude and latency over parietal cortices. Peripheral measures of arousal included skin conductance responses, heart rate and heart rate variance. Participants reported their perceived mental effort during each of the three attentional tasks. RESULTS: First, changes in arousal were seen from rest to completion of the three attentional tasks and between the attentional tasks. Changes seen between the attentional tasks being related to the task design and the attentional network activated. Second, perceived mental effort increased when demands of the task increased and correlated with left parietal beta band power during the three tasks of attention. Third, increased mental effort during the go/no-go task and the cued target detection task was inversely related to theta/beta ratios. CONCLUSION: These results indicate that perceived mental effort reflects tonic rather than phasic changes in arousal during tasks of attention. We suggest that perceived mental effort may reflect in part tonic activity of the LC-NE system in healthy individuals.

Frontal electroencephalogram asymmetry, salivary cortisol, and internalizing behavior problems in young adults who were born at extremely low birth weight.

The authors examined internalizing behavior problems at middle childhood, adolescence, and young adulthood and brain-based measures of stress vulnerability in 154 right-handed, nonimpaired young adults (M age = 23 years): 71 (30 males, 41 females) born at extremely low birth weight (ELBW; < 1,000 g) and 83 (35 males, 48 females) controls born at normal birth weight (NBW). Internalizing behavior problems increased from adolescence to young adulthood among ELBW individuals. ELBW adults exhibited greater relative right frontal electroencephalogram activity at rest and more concurrent internalizing behavior problems than NBW controls. Being born at ELBW may have subtle influences on brain-behavior relations even in survivors without major impairments and evidence of these influences may not emerge until young adulthood.

The effects of chewing-side preference on human brain activity during tooth clenching: an fMRI study.

Chewing-side preference (CSP) may be associated with dominant cerebral hemispheric organisation. However, little information exists regarding whether CSP is reflected by preferential activity in the opposite (to the CSP) cerebral hemisphere. The aim of this study was to investigate the effects of CSP on cerebral cortex response to bilateral tooth clenching. Sixteen right-handed participants with left (two men: 29·0±8·4 years old, six women: 32·3±4·8 years old) or right (four men: 31·0±6·1 years old, four women: 30·8±4·7 years old) CSP were scanned by functional magnetic resonance imaging during moderate levels of voluntary tooth clenching. The on-off sequence of scanning was 30 s of clenching (on) and 30 s of rest (off) a total of five times. The results showed that blood oxygen level-dependent signals in the contralateral (to the CSP) primary sensorimotor cortex increased more than in the ipsilateral primary sensorimotor cortex in participants with both left and right CSP (P≤0·001). The supplementary motor area was activated in participants with left (P≤0·001) but not right CSP. Activation of the inferior frontal gyrus and inferior parietal lobule was greater in participants with right versus left CSP (P≤0·001). Significant (P≤0·001) activation was observed in the parahippocampal gyrus in five of eight participants with left CSP, whereas no activation was observed in those with right CSP. These findings suggest a relationship between hemispheric dominance and CSP in the primary sensorimotor cortex responsible for bilateral tooth clenching.

Hemispheric prevalence during chewing in normal right-handed and left-handed subjects: a functional magnetic resonance imaging preliminary study.

This study evaluated the activation of different cortical areas during nondeliberate chewing of soft and hard boluses in five right-handed and five left-handed subjects with normal occlusion, to determine different hemispheric prevalences. The study was conducted with a functional Magnetic Resonance Imaging (1.5 T Magnetom Vision - Siemens Medical, Germany) using a head coil. The results showed that the most frequently activated areas were Brodmann's areas four and six in the primary motor and premotor cortex, the insula and Broca's area and, overall, showed greater activity of the cortical mastication area (CMA) in the right hemisphere for right-handed and in the left hemisphere for left-handed subjects.

Progesterone modulates theta oscillations in the frontal-parietal network.

The neuroactive metabolites of the steroid hormones progesterone (P4) and testosterone (T) are GABAergic modulators that influence cognition, yet, the specific effect of P4 and T on brain network activity remains poorly understood. Here, we investigated if a fundamental oscillatory network activity pattern, often related to cognitive control, frontal midline theta (FMT) oscillations, are modulated by steroids hormones, P4 and T. We measured the concentration of P4 and T using salivary enzyme immunoassay and FMT oscillations using high-density electroencephalography (EEG) during eyes-open resting-state in 55 healthy women and men. Electrical brain activity was analyzed using Fourier analysis, aperiodic signal fitting, and beamformer source localization. Steroid hormone concentrations and biological sex were used as predictors for scalp and source-estimated amplitude of theta oscillations. Elevated concentrations of P4 predicted increased amplitude of FMT oscillations across both sexes, and no relationship was found with T. The positive correlation with P4 was specific to the frontal midline electrodes and survived correction for the background aperiodic signal of the brain. Using source localization, FMT oscillations were localized to the frontal-parietal network (FPN). Additionally, theta amplitude within the FPN, but not the default mode network, positively correlated with P4 concentration. Our results suggest that P4 concentration modulates brain activity via upregulation of theta oscillations in the FPN.

Hemispheric Dominance for Language and Side Effects in Mapping the Inferior Frontal Junction Area with Transcranial Magnetic Stimulation.

BACKGROUND AND STUDY AIMS: Language mapping by navigated transcranial magnetic stimulation (TMS) is commonly applied over the left language-dominant hemisphere to indicate the language-related cortex. Detailed language mapping of Broca's region including stimulation targets in the immediate vicinity to the premotor cortex may raise concern about confounding unspecific motor effects. We performed interhemispheric comparisons to delineate such possible unspecific effects from true TMS-induced language inhibition. MATERIAL AND METHODS: Fifteen healthy German speakers named object pictures during navigated TMS over a left- and right-hemispheric target array covering the left inferior frontal junction area. Six mapping repetitions were conducted per hemisphere. Order of stimulation side was randomized between participants. Self-rating of discomfort was assessed after each stimulation; language errors and motor side effects were evaluated offline. RESULTS: Naming errors were observed significantly more frequently during left- than right-hemispheric stimulation. The same pattern was found for the most frequent error category of performance errors. Hierarchical cluster analyses of normalized ratings of error severity revealed a clear focus of TMS susceptibility for language inhibition in object naming at the dorsoposterior target sites only in the left hemisphere. We found no statistical difference in discomfort ratings between both hemispheres and also no interhemispheric difference in motor side effects, but we observed significantly stronger muscle contractions of the eyes as compared with the mouth. CONCLUSION: Our results of (1) unspecific pre-/motor effects similarly induced in both hemispheres, and (2) a specific focus of TMS susceptibility in the language-dominant hemisphere render any substantial contribution of nonlanguage-specific effects in TMS language mapping of the inferior frontal junction area highly unlikely.

Involvement of the basal nucleus of Meynert on regional cerebral cortical vasodilation associated with masticatory muscle activity in rats.

We examined the neural mechanisms for increases in regional cerebral blood flow (rCBF) in the neocortex associated with mastication, focusing on the cortical vasodilative system derived from the nucleus basalis of Meynert (NBM). In pentobarbital-anesthetized rats, parietal cortical rCBF was recorded simultaneously with electromyogram (EMG) of jaw muscles, local field potentials of frontal cortex, multi-unit activity of NBM neurons, and systemic mean arterial pressure (MAP). When spontaneous rhythmic EMG activity was observed with cortical desynchronization, an increase in NBM activity and a marked rCBF increase independent of MAP changes were observed. A similar rCBF increase was elicited by repetitive electrical stimulation of unilateral cortical masticatory areas. The magnitude of rCBF increase was partially attenuated by administration of the GABAergic agonist muscimol into the NBM. The rCBF increase persisted after immobilization with systemic muscle relaxant (vecuronium). rCBF did not change when jaw muscle activity was induced by electrical stimulation of the pyramidal tract. The results suggest that activation of NBM vasodilator neurons contributes at least in part to the rCBF increase associated with masticatory muscle activity, and that the NBM activation is induced by central commands from the motor cortex, independently of feedback from brainstem central pattern generator or contracting muscles.

Neurobiological correlates of coping through emotional approach.

This investigation considered possible health-related neurobiological processes associated with "emotional approach coping" (EAC), or intentional efforts to identify, process, and express emotions surrounding stressors. It was hypothesized that higher dispositional use of EAC strategies would be related to neural activity indicative of greater trait approach motivational orientation and to lower proinflammatory cytokine and cortisol responses to stress. To assess these relationships, 46 healthy participants completed a questionnaire assessing the two components of EAC (i.e., emotional processing and emotional expression), and their resting frontal cortical asymmetry was measured using electroencephalography (EEG). A subset (N=22) of these participants' levels of the soluble receptor for tumor necrosis factor-alpha (sTNFalphaRII), interleukin-6 (IL-6), and cortisol (all obtained from oral fluids) were also assessed before and after exposure to an acute laboratory stressor. Consistent with predictions, higher reported levels of emotional expression were significantly associated with greater relative left-sided frontal EEG asymmetry, indicative of greater trait approach motivation. Additionally, people who scored higher on EAC, particularly the emotional processing component, tended to show a less-pronounced TNF-alpha stress response. EAC was unrelated to levels of IL-6 and cortisol. Greater left-sided frontal EEG asymmetry was significantly related to lower baseline levels of IL-6 and to lower stress-related levels of sTNFalphaRII, and was marginally related to lower stress-related levels of IL-6. The findings suggest that the salubrious effects of EAC strategies for managing stress may be linked to an approach-oriented neurocognitive profile and to well-regulated proinflammatory cytokine responses to stress.

Separation of cellular from extracellular controls of drinking in rats by frontal brain damage.

Rats that had undergone removal of the frontal portion of the brain, including the olfactory bulbs, did not drink, or drank less than controls, when subjected to cellular dehydration. These same animals drank normally in response to extracellular volume reduction. Rats from which only the olfactory bulbs had been removed drank normally in both tests. An essential part of the neurological system mediating drinking produced by cellular dehydration, but not by volume reduction, therefore lies within the frontal cortex or immediate subcortical tissue.

Cerebral activations resulting from virtual dental treatment.

Pain, and anxiety of pain, for some people are serious problems in dental treatment. It is a common practical experience that even entering a dental surgery office, or the sound of a dental drill, may evoke vegetative correlates of toothache without any underlying disease. This everyday phenomenon suggests the hypothesis of a corresponding activation of pain-related brain areas by virtual dental treatment. Twenty healthy subjects viewed two different video clips presenting a dental treatment from the first-person perspective (simulation movie) and a moving hand holding an electrical toothbrush (control movie). Using functional magnetic resonance imaging, the cerebral hemodynamic responses that occurred during simulation and control movies were compared. Virtual dental treatment was associated with increased activity in pain-related brain areas such as the cingulate cortex, the insula, and primary and secondary somatosensory cortexes (SI, SII). The brain activation pattern indicates not only affective-motivational but also sensory-discriminative pain components during virtual dental treatment in all volunteers. Volunteers with a higher level of dental anxiety showed stronger activation of SI and SII. This may be a result of their higher anticipation of pain.

Uncovering the functional anatomy of the human insula during speech.

The contribution of insular cortex to speech production remains unclear and controversial given diverse findings from functional neuroimaging and lesional data. To create a precise spatiotemporal map of insular activity, we performed a series of experiments: single-word articulations of varying complexity, non-speech orofacial movements and speech listening, in a cohort of 27 patients implanted with penetrating intracranial electrodes. The posterior insula was robustly active bilaterally, but after the onset of articulation, during listening to speech and during production of non-speech mouth movements. Preceding articulation there was very sparse activity, localized primarily to the frontal operculum rather than the insula. Posterior insular was active coincident with superior temporal gyrus but was more active for self-generated speech than external speech, the opposite of the superior temporal gyrus. These findings support the conclusion that the insula does not serve pre-articulatory preparatory roles.