Neural Correlates of Appetite and Hunger-Related Evaluative Judgments

How much we desire a meal depends on both the constituent foods and how hungry we are, though not every meal becomes more desirable with increasing hunger. The brain therefore needs to be able to integrate hunger and meal properties to compute the correct incentive value of a meal. The present study investigated the functional role of the amygdala and the orbitofrontal cortex in mediating hunger and dish attractiveness. Furthermore, it explored neural responses to dish descriptions particularly susceptible to value-increase following fasting. We instructed participants to rate how much they wanted food menu items while they were either hungry or sated, and compared the rating differences in these states. Our results point to the representation of food value in the amygdala, and to an integration of attractiveness with hunger level in the orbitofrontal cortex. Dishes particularly desirable during hunger activated the thalamus and the insula. Our results specify the functions of evaluative structures in the context of food attractiveness, and point to a complex neural representation of dish qualities which contribute to state-dependent value

Neuropsychological patterns following lesions of the anterior insula in a series of forty neurosurgical patients

In the present study we investigated the effects of lesions affecting mainly the anterior insula in a series of 22 patients with lesions in the left hemisphere (LH), and 18 patients with lesions involving the right hemisphere (RH). The site of the lesion was established by performing an overlap of the probabilistic cytoarchitectonic maps of the posterior insula. Here we report the patients\u2019 neuropsychological profile and an analysis of their pre-surgical symptoms. We found that pre-operatory symptoms significantly differed in patients depending on whether the lesion affected the right or left insula and a strict parallelism between the patterns emerged in the pre-surgery symptoms analysis, and the patients\u2019 cognitive profile. In particular, we found that LH patients showed cognitive deficits. By contrast, the RH patients, with the exception of one case showing an impaired performance at the visuo-spatial planning test were within the normal range in performing all the tests. In addition, a sub-group of patients underwent to the post-surgery follow-up examination

Different representations of pleasant and unpleasant odours in the human brain.

Odours are important in emotional processing; yet relatively little is known about the representations of the affective qualities of odours in the human brain. We found that three pleasant and three unpleasant odours activated dissociable parts of the human brain. Pleasant but not unpleasant odours were found to activate a medial region of the rostral orbitofrontal cortex. Further, there was a correlation between the subjective pleasantness ratings of the six odours given during the investigation with activation of a medial region of the rostral orbitofrontal cortex. In contrast, a correlation between the subjective unpleasantness ratings of the six odours was found in regions of the left and more lateral orbitofrontal cortex. Moreover, a double dissociation was found with the intensity ratings of the odours, which were not correlated with the BOLD signal in the orbitofrontal cortex, but were correlated with the signal in medial olfactory cortical areas including the pyriform and anterior entorhinal cortex. Activation was also found in the anterior cingulate cortex, with a middle part of the anterior cingulate activated by both pleasant and unpleasant odours, and a more anterior part of the anterior cingulate cortex showing a correlation with the subjective pleasantness ratings of the odours. Thus the results suggest that there is a hedonic map of the sense of smell in brain regions such as the orbitofrontal cortex, and these results have implications for understanding the psychiatric and related problems that follow damage to these brain areas

Taste-related activity in the human dorsolateral prefrontal cortex.

Taste remains one of the least-explored human senses. Cortical taste responses were investigated using neuroimaging in 40 subjects tasting a range of different taste stimuli compared to a neutral tasteless control. Activation was found in the anterior insula/frontal opercular taste cortex and caudal orbitofrontal cortex, both areas established as taste cortical areas by neuronal recordings in primates. A novel finding in this study was a highly significant response to taste in the dorsolateral prefrontal cortex. This may reflect an effect of taste on cognitive processing to help optimise or modify behavioural strategies involved in executive control; or it could reflect the engagement of this region in attentional processing by a taste input

Representation of umami taste in the human brain.

Umami taste stimuli, of which an exemplar is monosodium glutamate (MSG) and which capture what is described as the taste of protein, were shown using functional MRI (fMRI) to activate similar cortical regions of the human taste system to those activated by a prototypical taste stimulus, glucose. These taste regions included the insular/opercular cortex and the caudolateral orbitofrontal cortex. A part of the rostral anterior cingulate cortex (ACC) was also activated. When the nucleotide 0.005 M inosine 5'-monophosphate (IMP) was added to MSG (0.05 M), the blood oxygenation-level dependent (BOLD) signal in an anterior part of the orbitofrontal cortex showed supralinear additivity; this may reflect the subjective enhancement of umami taste that has been described when IMP is added to MSG. These results extend to humans previous studies in macaques showing that single neurons in these taste cortical areas can be tuned to umami stimuli

Human cortical responses to water in the mouth, and the effects of thirst.

In an event-related functional magnetic resonance imaging (fMRI) study in humans it was shown, first, that water produces activations in cortical taste areas (in particular the frontal operculum/anterior insula which is the primate primary taste cortex, and the caudal orbitofrontal/secondary taste cortex) comparable to those produced by the prototypical tastants salt and glucose. Second, the activations in the frontal operculum/anterior insula produced by water when thirsty were still as large after the subjects had consumed water to satiety. Third, in contrast, the responses to water in the caudal orbitofrontal cortex were modulated by the physiological state of the body, in that responses to the oral delivery of water in this region were not found after the subjects had drunk water to satiety. Fourth, further evidence that the reward value or pleasantness of water is represented in the orbitofrontal cortex was that a positive correlation with the subjective ratings of the pleasantness of the water was found with activations in the caudal and anterior orbitofrontal cortex, and also in the anterior cingulate cortex. Fifth, it was found that a region of the middle part of the insula was also activated by water in the mouth, and further, that this activation only occurred when thirsty. Sixth, analyses comparing pre- and postsatiety periods (i.e., when thirsty and when not thirsty) independently of stimulus delivery revealed higher activity levels in the rostral anterior cingulate cortex. The activity of the rostral anterior cingulate cortex thus appears to reflect the thirst level or motivational state of the subjects

Human cortical responses to water in the mouth, and the effects of thirst.

In an event-related functional magnetic resonance imaging (fMRI) study in humans it was shown, first, that water produces activations in cortical taste areas (in particular the frontal operculum/anterior insula which is the primate primary taste cortex, and the caudal orbitofrontal/secondary taste cortex) comparable to those produced by the prototypical tastants salt and glucose. Second, the activations in the frontal operculum/anterior insula produced by water when thirsty were still as large after the subjects had consumed water to satiety. Third, in contrast, the responses to water in the caudal orbitofrontal cortex were modulated by the physiological state of the body, in that responses to the oral delivery of water in this region were not found after the subjects had drunk water to satiety. Fourth, further evidence that the reward value or pleasantness of water is represented in the orbitofrontal cortex was that a positive correlation with the subjective ratings of the pleasantness of the water was found with activations in the caudal and anterior orbitofrontal cortex, and also in the anterior cingulate cortex. Fifth, it was found that a region of the middle part of the insula was also activated by water in the mouth, and further, that this activation only occurred when thirsty. Sixth, analyses comparing pre- and postsatiety periods (i.e., when thirsty and when not thirsty) independently of stimulus delivery revealed higher activity levels in the rostral anterior cingulate cortex. The activity of the rostral anterior cingulate cortex thus appears to reflect the thirst level or motivational state of the subjects

Taste-olfactory convergence, and the representation of the pleasantness of flavour, in the human brain.

The functional architecture of the central taste and olfactory systems in primates provides evidence that the convergence of taste and smell information onto single neurons is realized in the caudal orbitofrontal cortex (and immediately adjacent agranular insula). These higher-order association cortical areas thus support flavour processing. Much less is known, however, about homologous regions in the human cortex, or how taste-odour interactions, and thus flavour perception, are implemented in the human brain. We performed an event-related fMRI study to investigate where in the human brain these interactions between taste and odour stimuli (administered retronasally) may be realized. The brain regions that were activated by both taste and smell included parts of the caudal orbitofrontal cortex, amygdala, insular cortex and adjoining areas, and anterior cingulate cortex. It was shown that a small part of the anterior (putatively agranular) insula responds to unimodal taste and to unimodal olfactory stimuli, and that a part of the anterior frontal operculum is a unimodal taste area (putatively primary taste cortex) not activated by olfactory stimuli. Activations to combined olfactory and taste stimuli where there was little or no activation to either alone (providing positive evidence for interactions between the olfactory and taste inputs) were found in a lateral anterior part of the orbitofrontal cortex. Correlations with consonance ratings for the smell and taste combinations, and for their pleasantness, were found in a medial anterior part of the orbitofrontal cortex. These results provide evidence on the neural substrate for the convergence of taste and olfactory stimuli to produce flavour in humans, and where the pleasantness of flavour is represented in the human brain

Methamphetamine activates reward circuitry in drug naive human subjects.

Amphetamines are highly addictive drugs that have pronounced effects on emotional and cognitive behavior in humans. These effects are mediated through their potent dopaminergic agonistic properties. Dopamine has also been implicated in the modulation of responses of the 'reward circuit' in animal and human studies. In this study we use functional magnetic resonance imaging (fMRI) to identify the brain circuitry involved in the psychostimulant effect of methamphetamine in psychostimulant-naïve human subjects. Seven healthy volunteers were scanned in a 3T MR imaging system. They received single-blind intravenous infusions of methamphetamine (0.15 mg/kg), and rated their experience of 'mind-racing' on a button press throughout the experiment. Data were analyzed with statistical parametric mapping methods. Amphetamine administration activated the medial orbitofrontal cortex, the rostral part of the anterior cingulate cortex, and the ventral striatum. Ratings of 'mind-racing' after methamphetamine infusion correlated with activations in the rostral part of the anterior cingulate cortex and in the ventral striatum. In addition, activations in the medial orbitofrontal cortex were independent of motor and related responses involved in making the ratings. These findings indicate that the first administration of a psychostimulant to human subjects activates classical reward circuitry. Our data also support recent hypotheses suggesting a central role for the orbitofrontal cortex in drug reinforcement and the development of addiction