The role of the insular cortex in taste function

In spite of over 30 years of research, the role of the Insular Cortex (IC) in taste memory still remains elusive. To study the role of the IC in taste memory, we used conditioned taste aversion (CTA) for two different concentrations of saccharin; 0.1% which is highly preferred, and 0.5% which is non-preferred. Rats that had been IC lesioned bilaterally with ibotenic acid (15 mg/ml) before CTA showed significant learning impairments for saccharin 0.1% but not for saccharin 0.5%. To test CTA memory retention, rats lesioned a week after CTA training became completely amnesic for saccharin 0.1% yet only mildly impaired for saccharin 0.5%. Interestingly, the resulting preference for either concentration matched that of IC lesioned animals when exposed to either saccharin solution for the first time, but not those of sham animals, implying that IC lesions after CTA for either saccharin solution rendered complete amnesia, irrespective of the original preference. Our data indicate that an intact IC is essential for CTA learning and retention, as well as for an early neophobic response, but not for taste preference itself. Our data supports a model where the IC is involved in general taste rejection.     

A twin study of spatial and non-spatial delayed response performance in middle age

Delayed alternation and object alternation are classic spatial and non-spatial delayed response tasks. We tested 632 middle-aged male veteran twins on variants of these tasks in order to compare test difficulty, measure their inter-correlation, test order effects, and estimate heritabilities (proportion of observed variance due to genetic influences). Non-spatial alternation (NSA), which may involve greater reliance on processing of subgoals, was significantly more difficult than spatial alternation (SA). Despite their similarities, NSA and SA scores were uncorrelated. NSA performance was worse when administered second; there was no SA order effect. NSA scores were modestly heritable (h(2)=.25; 26); SA was not. There was shared genetic variance between NSA scores and general intellectual ability (r(g)=.55; .67), but this also suggests genetic influences specific to NSA. Compared with findings from small, selected control samples, high "failure" rates in this community-based sample raise concerns about interpretation of brain dysfunction in elderly or patient samples.     

Impairments in tactile search following superior parietal damage

The superior parietal cortex is critical for the control of visually guided actions. Research suggests that visual stimuli relevant to actions are preferentially processed when they are in peripersonal space. One recent study demonstrated that visually guided movements towards the body were more impaired in a patient with damage to superior parietal cortex. Whereas past studies have explored disordered movement in optic ataxic patients, there has been less exploration of space perception in terms of search capacity in this population. In addition, there is some debate concerning the relationship between deficits of visuomotor control and impaired attention/perception in optic ataxia. Given that the dorsal stream has been implicated in the spatial processing of stimuli in peripersonal space, and damage to this region is known to cause optic ataxia, we felt that further investigation was warranted. We examined tactile search behavior in the fronto-parallel and radial planes in a patient with right superior parietal damage and optic ataxia. We used a pegboard with removable cylindrical pegs that allowed for the reorganization of targets between trials. To better characterize three-dimensional search behavior, we included both horizontal and vertical search conditions. Results showed that the patient spent more time searching, was more accurate and revisited more targets in right versus left space. Interestingly, the patient spent the majority of her time specifically searching the lower right quadrant of the stimulus array. Further analysis revealed lower target detection rates along the outer borders of the pegboard on all sides. The search pattern observed here is unusual considering that all targets were within arm's reach. The present experiment demonstrates that damage to superior parietal cortex impairs tactile search and biases exploration towards lower right peripersonal space.     

A brief review on the use of functional near-infrared spectroscopy (fNIRS) for language imaging studies in human newborns and adults

Upon stimulation, real time maps of cortical hemodynamic responses can be obtained by non-invasive functional near-infrared spectroscopy (fNIRS) which measures changes in oxygenated and deoxygenated hemoglobin after positioning multiple sources and detectors over the human scalp. The current commercially available transportable fNIRS systems have a time resolution of 1-10 Hz, a depth sensitivity of about 1.5 cm, and a spatial resolution of about 1 cm. The goal of this brief review is to report infants, children and adults fNIRS language studies. Since 1998, 60 studies have been published on cortical activation in the brain’s classic language areas in children/adults as well as newborns using fNIRS instrumentations of different complexity. In addition, the basic principles of fNIRS including features, strengths, advantages, and limitations are summarized in terms that can be understood even by non specialists. Future prospects of fNIRS in the field of language processing imaging are highlighted.     

Neural correlates of feigned memory impairment are distinguishable from answering randomly and answering incorrectly: an fMRI and behavioral study

Previous functional magnetic resonance imaging (fMRI) studies have identified activation in the prefrontal-parietal-sub-cortical circuit during feigned memory impairment when comparing with truthful telling. Here, we used fMRI to determine whether neural activity can differentiate between answering correctly, answering randomly, answering incorrectly, and feigned memory impairment. In this study, 12 healthy subjects underwent block-design fMRI while they performed digit task of forced-choice format under four conditions: answering correctly, answering randomly, answering incorrectly, and simulated feigned memory impairment. There were three main results. First, six areas, including the left prefrontal cortex, the left superior temporal lobe, the right postcentral gyrus, the right superior parietal cortex, the right superior occipital cortex, and the right putamen, were significantly modulated by condition type. Second, for some areas, including the right superior parietal cortex, the right postcentral gyrus, the right superior occipital cortex, and the right putamen, brain activity was significantly greater in feigned memory impairment than answering randomly. Third, for the areas including the left prefrontal cortex and the right putamen, brain activity was significantly greater in feigned memory impairment than answering incorrectly. In contrast, for the left superior temporal lobe, brain activity was significantly greater in answering incorrectly than feigned memory impairment. The results suggest that neural correlates of feigned memory impairment are distinguishable from answering randomly and answering incorrectly in healthy subjects.     

Muscarinic cholinergic receptor blockade in the rat prelimbic cortex impairs the social transmission of food preference

Previous findings demonstrate the involvement of the cholinergic NBM in the acquisition of the social transmission of food preference (STFP), a relational associative odor-guided learning task. There is also evidence that muscarinic receptors in the medial prefrontal cortex, an important NBM target area, may modulate olfactory associative memory. The present experiment determined the consequences of blocking muscarinic cholinergic receptors in a component of the medial prefrontal region (the prelimbic cortex) on the STFP task. Adult male Wistar rats were bilaterally infused with scopolamine (20 microg/site) prior to training and showed a severe impairment in the expression of the task measured in two retention sessions, both immediately and 24h after training. Local scopolamine injections in the prelimbic cortex did not affect other behavioral measures such as olfactory perception, social interaction, motivation to eat, neophobia, or exploration. Results suggest that muscarinic transmission in the prelimbic cortex is essential for the STFP, supporting the hypothesis that ACh in a specific prefrontal area is important for this naturalistic form of olfactory relational memory. Current data are discussed in the context of disruption of learning as a result of interferences in PLC functions such as behavioral flexibility, attention, and strategic planning.     

The role of visual experience on the representation and updating of novel haptic scenes

We investigated the role of visual experience on the spatial representation and updating of haptic scenes by comparing recognition performance across sighted, congenitally and late blind participants. We first established that spatial updating occurs in sighted individuals to haptic scenes of novel objects. All participants were required to recognise a previously learned haptic scene of novel objects presented across the same or different orientation as learning whilst they either remained in the same position to moved to a new position relative to the scene. Scene rotation incurred a cost in recognition performance in all groups. However, overall haptic scene recognition performance was worse in the congenitally blind group. Moreover, unlike the late blind or sighted groups, the congenitally blind group were unable to compensate for the cost in scene rotation with observer motion. Our results suggest that vision plays an important role in representing and updating spatial information encoded through touch and have important implications for the role of vision in the development of neuronal areas involved in spatial cognition.     

Mental time travel,somatic markers and “myopia for the future”

Patients with damage to the ventromedial prefrontal cortex (VMPFC) are often described as having impaired ability for planning and decision making despite retaining intact capacities for explicit reasoning. The somatic marker hypothesis is that the VMPFC associates implicitly represented affective information with explicit representations of actions or outcomes. Consequently, when the VMPFC is damaged explicit reasoning is no longer scaffolded by affective information, leading to characteristic deficits. These deficits are exemplified in performance on the Iowa Gambling Task (IGT) in which subjects with VMPFC perform significantly worse than neurotypicals in a task which requires them learn from rewarding and punishing experience to make decisions. The somatic marker theory adopts a canonical theory of emotion, in which emotions function as part of a valencing system, to explain the role of affective processes. The first part of the paper argues against this canonical account. The second part provides a different account of the role of the role of the VMPFC in decision-making which does not depend on the canonical account of emotion. Together the first and second parts of the paper provide the basis for a different interpretation of results on the Iowa Gambling Task (IGT). In fact the IGT may be probing a deficit in what has been called mental time travel: the ability to access and use information from previous experience and imaginatively rehearse future experiences as part of the process of deliberation.     

风险决策的神经机制:基于啮齿类动物研究

风险决策是在不同选项的结果确定、并且结果出现的概率已知情况下的决策。啮齿类风险决策模型研究发现前额皮层-杏仁核-伏隔核神经环路联系是决定风险决策的选择倾向的关键。前额皮层中的眶额皮层和内侧前额皮层参与风险决策的策略形成和策略转换有关;而皮层下核团中的杏仁核、腹侧纹状体的伏隔核等结构参与策略保持、价值判断,影响决策偏向和行动强度;眶额皮层、伏隔核神经元和多巴胺神经元编码风险决策过程中的概率、风险等因素;此外,多巴胺等单胺类神经递质及受体在风险决策中有复杂的作用。