Kay Head

The Effect of Flavanol-rich Cocoa on the fMRI Response to a Cognitive Task in Healthy Young People

Flavanols are the main flavonoids found in cocoa and chocolate, and can be especially abundant in certain cocoas. Research over the past decade has identified flavanols as showing diverse beneficial physiologic and antioxidant effects, particularly in context of vascular function. The present study employed functional magnetic resonance imaging based on blood oxygenation level-dependent (BOLD) contrast to explore the effect of flavanols on the human brain. Magnetic resonance imaging was used to measure BOLD responses to a cognitive task in 16 healthy young subjects. The data presented show an increase in the BOLD signal intensity in response to a cognitive task following ingestion of flavanol-rich cocoa (5 days of 150 mg of cocoa flavanols). This may arise either as a result of altered neuronal activity, or a change in vascular responsiveness, or both—the net effect then being dependent on which of the two effects is dominant. No significant effects were evident in behavioral reaction times, switch cost, and heart rate after consumption of this moderate dose of cocoa flavanols. A pilot study evaluated the relationship between cerebral blood flow and a single acute dose (450 mg flavanols) of flavanol-rich cocoa and showed that flavanol-rich cocoa can increase the cerebral blood flow to gray matter, suggesting the potential of cocoa flavanols for treatment of vascular impairment, including dementia and strokes, and thus for maintaining cardiovascular health.

fMRI at 1.5, 3 and 7 T: characterising BOLD signal changes

Blood oxygenation level dependent (BOLD) signal changes occurring during execution of a simple motor task were measured at field strengths of 1.5, 3 and 7 T using multi-slice, single-shot, gradient echo EPI at a resolution of 1x1x3 mm(3), to quantify the benefits offered by ultra-high magnetic field for functional MRI. Using four different echo times at each field strength allowed quantification of the relaxation rate, R(2)* and the change in relaxation rate on activation, DeltaR(2)*. This work adds to previous studies of the field strength dependence of BOLD signal characteristics, through its: (i) focus on motor rather than visual cortex; (ii) use of single-shot, multi-slice, gradient echo EPI for data acquisition; (iii) co-registration of images acquired at different field strengths to allow assessment of the BOLD signal changes in the same region at each field strength. DeltaR(2)* was found to increase linearly with field strength (0.51+/-0.06 s(-1) at 1.5 T; 0.98+/-0.08 s(-1) at 3 T; 2.55+/-0.22 s(-1) at 7 T), while the ratio of DeltaR(2)*/R(2), which dictates the accessible BOLD contrast was also found to increase (0.042+/-0.002 at 1.5 T; 0.054+/-0.002 at 3 T; 0.084+/-0.003 at 7 T). The number of pixels classified as active, the t-value calculated over a common region of interest and the percentage signal change in the same region were all found to peak at TE approximately T(2)* and increase significantly with field strength. An earlier onset of the haemodynamic response at higher field provides some evidence for a reduced venous contribution to the BOLD signal at 7 T.

Improved methods for fMRI studies of combined taste and aroma stimuli.

Previous neuroimaging studies of the cortical representation of gustatory and olfactory stimuli have often delivered tastants to the mouth in very small quantities or stimulated olfaction orthonasally. In studies of retro-nasal olfaction, swallowing was generally delayed to reduce head motion artefacts. The present fMRI study aims to improve upon such methodological limitations to allow investigation of the cortical representation of flavour (taste and aroma combination) as it typically occurs during the consumption of liquid foods. For this purpose we used (1) a novel, automated, sprayed stimulus delivery system and a larger volume of liquid sample (containing sweet tastants and banana/pear aroma volatiles) to achieve more extensive stimulation of the oral cavity taste receptors, (2) a pseudo-natural delivery paradigm that included prompt swallowing after each sample delivery to obtain physiological retro-nasal olfactory stimulation, (3) fMRI acquisition with wide brain coverage and double-echo EPI to improve sensitivity. We validated our paradigm for the delivery of volatiles using atmospheric pressure chemical ionisation mass spectrometry. This showed that the main retro-nasal delivery of volatiles in the paradigm occurs immediately after the swallow. Several brain areas were found to be activated, including the insula, frontal operculum, rolandic operculum/parietal lobe, piriform, dorsolateral prefrontal cortex, anterior cingulate cortex, ventro-medial thalamus, hippocampus and medial orbitofrontal cortex.

The cortical response to the oral perception of fat emulsions and the effect of taster status

The rewarding attributes of foods containing fat are associated with the increase in fat consumption, but little is known of how the complex physical and chemical properties of orally ingested fats are represented and decoded in the brain nor how this impacts feeding behavior within the population. Here, functional MRI (fMRI) is used to assess the brain response to isoviscous, isosweet fat emulsions of increasing fat concentration and to investigate the correlation of behavioral and neuroimaging responses with taster status (TS). Cortical areas activated in response to fat, and those areas positively correlated with fat concentration, were identified. Significant responses that positively correlated with increasing fat concentration were found in the anterior insula, frontal operculum and secondary somatosensory cortex (SII), anterior cingulate cortex, and amygdala. Assessing the effect of TS revealed a strong correlation with self-reported preference of the samples and with cortical response in somatosensory areas [primary somatosensory cortex (SI), SII, and midinsula] and the primary taste area (anterior insula) and a trend in reward areas (amygdala and orbitofrontal cortex). This finding of a strong correlation with TS in somatosensory areas supports the theory of increased mechanosensory trigeminal innervation in high 6-n-propyl-2-thiouracil (PROP) tasters and has been linked to a higher risk of obesity. The interindividual differences in blood oxygenation level-dependent (BOLD) amplitude with TS indicates that segmenting populations by TS will reduce the heterogeneity of BOLD responses, improving signal detection power.

Brain localization of memory chunks in chessplayers.

Chess experts store domain-specific representations in their long-term memory; due to the activation of such representations, they perform with high accuracy in tasks that require the maintenance of previously seen information. Chunk-based theories of expertise (chunking theory: ; template theory: ) state that expertise is acquired mainly by the acquisition and storage in long-term memory of familiar chunks that allow quick recognition. This study tested some predictions of these theories by using fMRI while chessplayers performed a recognition memory task. These theories predict that chessplayers access long-term memory chunks of domain-specific information, which are presumably stored in the temporal lobes. It was also predicted that the recognition memory tasks would activate working memory areas in the frontal and parietal lobes. These predictions were supported by the data.

Binaural specialisation in human auditory cortex: an fMRI investigation of interaural correlation sensitivity

A listeners sensitivity to the interaural correlation (IAC) of sound plays an important role in several phenomena in binaural hearing. Although IAC has been examined humans, little is known about the neural basis of sensitivity to IAC in humans. The present study employed functional magnetic resonance imaging to measure blood oxygen level-dependent (BOLD) activity in auditory brainstem and cortical structures in human listeners during presentation of band-pass noise stimuli between which IAC was varied systematically. The stimuli evoked significant bilateral activation in the inferior colliculus, medial geniculate body, and auditory cortex. There was a significant positive relationship between BOLD activity and IAC which was confined to a distinct subregion of primary auditory cortex located bilaterally at the lateral extent of Heschls gyrus. Comparison with published anatomical data indicated that this area may also be cytoarchitecturally distinct. Larger differences in activation were found between levels of IAC near unity than between levels near zero. This response pattern is qualitatively compatible with previous measures of psychophysical and neurophysiological sensitivity to IAC. extensively in neurophysiological studies in animals and in psychophysical studies in

Alpha-gamma interactions are disturbed in schizophrenia: a fusion of electroencephalography and functional magnetic resonance imaging.

OBJECTIVE To delineate regional brain activity associated with the alpha oscillations related to perception of sensory stimuli, and test the hypothesis that the synchronisation of alpha oscillations with stimulus onset is impaired in schizophrenia. METHODS Joint independent component analysis was applied to electroencephalographic and functional magnetic resonance imaging data recorded in 19 individuals with schizophrenia and 19 healthy individuals during a vibrotactile somatosensory task. RESULTS In healthy individuals the strongest component was dominated by alpha oscillations, and was associated not only with activity in somatosensory regions but also in the insula and anterior cingulate cortex (the salience network). In schizophrenia, the strongest component had low alpha power and activity was limited mainly to somatosensory regions. Furthermore, in the healthy group, but not the patients, significant correlation was observed between the strongest component and evoked gamma power. CONCLUSION The correlation between the alpha-dominated component and evoked gamma power is consistent with the hypothesis that gamma localised to sensory cortex elicits stimulus-locking of spatially distinct, large-scale ongoing alpha oscillations. Furthermore, this hypothesised mechanism appears to be disrupted in schizophrenia. SIGNIFICANCE These findings suggest that a weakened alpha-gamma interaction underlies impaired recruitment of the brain during sensory information processing in schizophrenia.

fMRI and MEG analysis of visceral pain in healthy volunteers.

Background  Although many studies of painful rectal stimulation have found activation in the insula, cingulate, somatosensory, prefrontal cortices and thalamus, there is considerable variability when comparing functional magnetic resonance imaging (fMRI) results. Multiple factors may be responsible, including the model used in fMRI data analysis. Here, we assess the temporal response of activity to rectal barostat distension using novel fMRI and magnetoencephalography (MEG) analysis.

Evidence for reduced somatosensory lateralisation and focalisation in schizophrenia

Neuroimaging studies indicate diminished lateralisation of cerebral activity during motor tasks and language processing in schizophrenia. Some evidence also indicates that decreased lateralisation is accompanied by more diffuse intra-hemispheric activation, suggesting that diminished lateralisation might be part of a more general diminution of regional functional specialisation. In the case of passive processing of elementary somatosensory stimuli, evidence for decreased lateralisation derived from event-related potential studies, is conflicting. The greater spatial resolution of functional magnetic resonance imaging (fMRI) offers the potential to resolve this conflict. We report an fMRI study of 22 right-handed individuals with schizophrenia, 21 right-handed healthy individuals and 10 non-right-handed healthy individuals, designed to test the hypothesis that in schizophrenia there is a diminution of both lateralisation and intra-hemispheric focalisation during the passive processing of vibrotactile stimuli delivered to the right index finger. Significantly reduced lateralisation of activity in primary somatosensory cortex (SI) was observed in the schizophrenia group as compared to the healthy right-handed group. There was a trend for a reduction in SI lateralisation in the schizophrenia group compared to the healthy non-right-handed group. Contralateral SI focalisation was also significantly reduced in the schizophrenia group compared to both healthy groups. SI focalisation was negatively correlated with severity of disorganisation symptoms in the schizophrenia group. These results support the hypothesis that a generalised loss of functional specialisation is fundamental to schizophrenia.

Left lateralization in autobiographical memory: An fMRI study using the expert archival paradigm

In brain-imaging and behavioral research, studies of autobiographical memory have higher ecological validity than controlled laboratory memory studies. However, they also have less controllability over the variables investigated. This article presents a novel technique—the expert archival paradigm—that increases controllability while maintaining ecological validity. Stimuli were created from games played by two international-level chess masters. The two players were asked to perform a memory task with stimuli generated from their own games and stimuli generated from other players’ games while they were scanned using fMRI. The study found a left lateralized pattern of brain activity that was very similar in both masters. The brain areas activated were the left temporo-parietal junction and left frontal areas. The expert archival paradigm has the advantage of not requiring an interview to assess the participants’ autobiographical memories, and affords the possibility of measuring their accuracy of remembering as well as their brain activity related to remote and recent memories. It can also be used in any field of expertise, including arts, sciences, and sports, in which archival data are available.