Lori Haase

Cortical Activation in Response to Pure Taste Stimuli During the Physiological States of Hunger and Satiety

This event-related functional magnetic resonance imaging (er-fMRI) study investigated BOLD signal change in response to a series of pure gustatory stimuli that varied in stimulus quality when subjects were hungry and sated with a nutritional pre-load. Group analyses showed significant differences in activation in the hunger minus satiety condition in response to sucrose, caffeine, saccharin, and citric acid within the thalamus, hippocampus, and parahippocampus. When examining the hunger and satiety conditions, activation varied as a function of stimulus, with the majority of the stimuli exhibiting significantly greater activation in the hunger state within the insula, thalamus, and substantia nigra, in contrast to decreased activation in the satiated state within the parahippocampus, hippocampus, amygdala, and anterior cingulate. Region of interest (ROI) analysis revealed two significant interactions, ROI by physiology and ROI by physiology by stimulus. In the satiety condition, the primary (inferior and superior insulae) and secondary (OFC 11 and OFC 47) taste regions exhibited significantly greater brain activation in response to all stimuli than regions involved in processing eating behavior (hypothalamus), affect (amygdala), and memory (hippocampus, parahippocampus and entorhinal cortex). These same regions demonstrated significantly greater activation within the hunger condition than the satiety condition, with the exception of the superior insula. Furthermore, the patterns of activation differed as a function taste stimulus, with greater activation in response to sucrose than to the other stimuli. These differential patterns of activation suggest that the physiological states of hunger and satiety produce divergent activation in multiple brain areas in response to different pure gustatory stimuli.

Reduced nucleus accumbens and caudate nucleus activation to a pleasant taste is associated with obesity in older adults.

Although obesity is recognized as a global health epidemic, insufficient research has been directed to understanding the rising prevalence of obesity in the fastest growing segment of the population, older adults. Late-life obesity has been linked to declines in physical health and cognitive function, with implications not only for the individual, but also for society. We investigated the hypothesis that altered brain responses to food reward is associated with obesity, using fMRI of response to pleasant and aversive taste stimuli in young and older adults performing a hedonic evaluation task. Correlations between higher levels of abdominal fat/body mass index and reduced fMRI activation to sucrose in dopamine-related brain regions (caudate, nucleus accumbens) were large in older adults. Significant associations between a hypofunctioning reward response and obesity suggest the hypothesis that decreased dopamine functioning may be a plausible mechanism for weight gain in older adults.

Modifying Resilience Mechanisms in At-Risk Individuals: A Controlled Study of Mindfulness Training in Marines Preparing for Deployment

OBJECTIVE Military deployment can have profound effects on physical and mental health. Few studies have examined whether interventions prior to deployment can improve mechanisms underlying resilience. Mindfulness-based techniques have been shown to aid recovery from stress and may affect brain-behavior relationships prior to deployment. The authors examined the effect of mindfulness training on resilience mechanisms in active-duty Marines preparing for deployment. METHOD Eight Marine infantry platoons (N=281) were randomly selected. Four platoons were assigned to receive mindfulness training (N=147) and four were assigned to a training-as-usual control condition (N=134). Platoons were assessed at baseline, 8 weeks after baseline, and during and after a stressful combat training session approximately 9 weeks after baseline. The mindfulness training condition was delivered in the form of 8 weeks of Mindfulness-Based Mind Fitness Training (MMFT), a program comprising 20 hours of classroom instruction plus daily homework exercises. MMFT emphasizes interoceptive awareness, attentional control, and tolerance of present-moment experiences. The main outcome measures were heart rate, breathing rate, plasma neuropeptide Y concentration, score on the Response to Stressful Experiences Scale, and brain activation as measured by functional MRI. RESULTS Marines who received MMFT showed greater reactivity (heart rate [d=0.43]) and enhanced recovery (heart rate [d=0.67], breathing rate [d=0.93]) after stressful training; lower plasma neuropeptide Y concentration after stressful training (d=0.38); and attenuated blood-oxygen-level-dependent signal in the right insula and anterior cingulate. CONCLUSIONS The results show that mechanisms related to stress recovery can be modified in healthy individuals prior to stress exposure, with important implications for evidence-based mental health research and treatment.

Males and females show differential brain activation to taste when hungry and sated in gustatory and reward areas.

Although males and females differ in eating behavior and prevalence rates for eating disorders and obesity, little is known about gender differences in cortical activation to pleasant and unpleasant pure tastes during the physiological states of hunger and satiety. Twenty-one healthy young adults (12 females and 9 males) underwent two functional magnetic resonance imaging scans. Using four pure tastants of differing qualities (i.e., salty, sour, bitter, sweet), the present study examined gender differences in fMRI activation during two motivational states (hunger and satiety). There was greater change in fMRI activation from hunger to satiety in males than females in response to all tastes within the middle frontal gyrus (BA 10), insula, and cerebellum. Males also had greater change in activation from hunger to satiety, relative to females, in limbic regions including dorsal striatum, amygdala, parahippocampal gyrus, and posterior and anterior cingulate; however, activation was stimulus dependent, despite equivalent ratings in perceived pleasantness and intensity. Interestingly, males and females showed significant change from hunger to satiety in response to citric acid, suggesting that in addition to gender and physiological condition, stimulus quality is an important factor in taste fMRI activation. These gender differences may have implications for the pathophysiology of eating disorders and obesity.

Mindfulness-based training attenuates insula response to an aversive interoceptive challenge

Neuroimaging studies of mindfulness training (MT) modulate anterior cingulate cortex (ACC) and insula among other brain regions, which are important for attentional control, emotional regulation and interoception. Inspiratory breathing load (IBL) is an experimental approach to examine how an individual responds to an aversive stimulus. Military personnel are at increased risk for cognitive, emotional and physiological compromise as a consequence of prolonged exposure to stressful environments and, therefore, may benefit from MT. This study investigated whether MT modulates neural processing of interoceptive distress in infantry marines scheduled to undergo pre-deployment training and deployment to Afghanistan. Marines were divided into two groups: individuals who received training as usual (control) and individuals who received an additional 20-h mindfulness-based mind fitness training (MMFT). All subjects completed an IBL task during functional magnetic resonance imaging at baseline and post-MMFT training. Marines who underwent MMFT relative to controls demonstrated a significant attenuation of right anterior insula and ACC during the experience of loaded breathing. These results support the hypothesis that MT changes brain activation such that individuals process more effectively an aversive interoceptive stimulus. Thus, MT may serve as a training technique to modulate the brains response to negative interoceptive stimuli, which may help to improve resilience.

Treatment approaches for interoceptive dysfunctions in drug addiction

There is emerging evidence that individuals with drug addiction have dysfunctions in brain systems that are important for interoceptive processing, which include, among others, the insular and the anterior cingulate cortices. These individuals may not be expending sufficient neural resources to process perturbations of the interoceptive state but may exert over-activation of these systems when processing drug-related stimuli. As a consequence, insufficient detection and processing of interoceptive state changes may result in inadequate anticipation and preparation to adapt to environmental challenges, e.g., adapt to abstinence in the presence of withdrawal symptoms. Here, we integrate interoceptive dysfunction in drug-addicted individuals, with the neural basis for meditation and exercise to develop a heuristic to target the interoceptive system as potential treatments for drug addiction. First, it is suggested that mindfulness-based approaches can modulate both interoceptive function and insular activation patterns. Second, there is an emerging literature showing that the regulation of physical exercise in the brain involves the insula and anterior cingulate cortex and that intense physical exercise is associated with a insula changes that may provide a window to attenuate the increased interoceptive response to drug-related stimuli. It is concluded that the conceptual framework of interoceptive dysfunctions in drug addiction and the experimental findings in meditation and exercise provide a useful approach to develop new interventions for drug addiction.

Effect of Magnitude Estimation of Pleasantness and Intensity on fMRI Activation to Taste.

The goal of the present study was to investigate whether the psychophysical evaluation of taste stimuli using magnitude estimation influences the pattern of cortical activation observed with neuroimaging. That is, whether different brain areas are involved in the magnitude estimation of pleasantness relative to the magnitude estimation of intensity. fMRI was utilized to examine the patterns of cortical activation involved in magnitude estimation of pleasantness and intensity during hunger in response to taste stimuli. During scanning, subjects were administered taste stimuli orally and were asked to evaluate the perceived pleasantness or intensity using the general Labeled Magnitude Scale (Green et al., Chem Senses, 21(3), 323-334, 1996; Bartoshuk et al., Physiol Behav, 82(1), 109-114, 2004). Image analysis was conducted using Analysis of Functional NeuroImage software. Magnitude estimation of intensity and pleasantness shared common activations in the insula, rolandic operculum, and the medio-dorsal nucleus of the thalamus. Globally, magnitude estimation of pleasantness produced significantly more activation than magnitude estimation of intensity. Areas differentially activated during magnitude estimation of pleasantness versus intensity included, e.g., the insula, the anterior cingulate gyrus, and putamen, suggesting that different brain areas were recruited when subjects made magnitude estimates of intensity and pleasantness. These findings demonstrate significant differences in brain activation during magnitude estimation of intensity and pleasantness to taste stimuli. An appreciation for the complexity of brain response to taste stimuli may facilitate a clearer understanding of the neural mechanisms underlying eating behavior and overconsumption.

Can age-related CNS taste differences be detected as early as middle age? Evidence from fMRI.

Middle-aged Americans have higher obesity rates than any other age group, yet little is known about age-related changes in central taste function during this critical time. Research on taste and aging has primarily focused on psychophysical responses, and on older adults. Central taste processing in middle-age has not been investigated. In the current study, we compared functional magnetic resonance imaging (fMRI) activation of young and middle-aged adults during hedonic evaluation of a sweet and a bitter taste. A 2 (age group) by 2 (tastant) analysis of variance (ANOVA) on fMRI activation revealed: (1) a main effect of age (young adults>middle-aged adults) in the bilateral anterior cingulate, lentiform nucleus, putamen, caudate, and right precentral gyrus; (2) a main effect of taste (sweet>bitter) in the bilateral pre- and postcentral gyri, anterior cingulate and right middle frontal gyrus; qualified by (3) an age-by-taste interaction. Further inspection of the age-by-taste interaction revealed that there was a significant effect of age (greater activation in young adults) in sensory (insula) and reward (lentiform nucleus) regions during hedonic evaluation of the sweet taste; however, there was no age effect in the bitter taste condition. Further, young adults had greater responses during hedonic evaluation of sucrose than of caffeine in several sensory and motor processing regions (pre- and postcentral gyri, insula), but there were no taste-related differences in activation in the middle-aged adults. We speculate that these results might reflect early age-related differences in central taste processing that occur prior to deficits in gustatory function observed in old age, and this might have important implications for weight changes that occur during middle-age.

A pilot study investigating changes in neural processing after mindfulness training in elite athletes

The ability to pay close attention to the present moment can be a crucial factor for performing well in a competitive situation. Training mindfulness is one approach to potentially improve elite athletes’ ability to focus their attention on the present moment. However, virtually nothing is known about whether these types of interventions alter neural systems that are important for optimal performance. This pilot study examined whether an intervention aimed at improving mindfulness [Mindful Performance Enhancement, Awareness and Knowledge (mPEAK)] changes neural activation patterns during an interoceptive challenge. Participants completed a task involving anticipation and experience of loaded breathing during functional magnetic resonance imaging recording. There were five main results following mPEAK training: (1) elite athletes self-reported higher levels of interoceptive awareness and mindfulness and lower levels of alexithymia; (2) greater insula and anterior cingulate cortex (ACC) activation during anticipation and post-breathing load conditions; (3) increased ACC activation during the anticipation condition was associated with increased scores on the describing subscale of the Five Facet Mindfulness Questionnaire; (4) increased insula activation during the post-load condition was associated with decreases in the Toronto Alexithymia Scale identifying feelings subscale; (5) decreased resting state functional connectivity between the PCC and the right medial frontal cortex and the ACC. Taken together, this pilot study suggests that mPEAK training may lead to increased attention to bodily signals and greater neural processing during the anticipation and recovery from interoceptive perturbations. This association between attention to and processing of interoceptive afferents may result in greater adaptation during stressful situations in elite athletes.

When the brain does not adequately feel the body: Links between low resilience and interoception

This study examined neural processes of resilience during aversive interoceptive processing. Forty-six individuals were divided into three groups of resilience Low (LowRes), high (HighRes), and normal (NormRes), based on the Connor-Davidson Resilience Scale (2003). Participants then completed a task involving anticipation and experience of loaded breathing during functional magnetic resonance imaging (fMRI) recording. Compared to HighRes and NormRes groups, LowRes self-reported lower levels of interoceptive awareness and demonstrated higher insular and thalamic activation across anticipation and breathing load conditions. Thus, individuals with lower resilience show reduced attention to bodily signals but greater neural processing to aversive bodily perturbations. In low resilient individuals, this mismatch between attention to and processing of interoceptive afferents may result in poor adaptation in stressful situations.