Functional neuroanatomical correlates of contingency judgement.

Contingency judgement is an ability to detect relationships between events and is crucial in the allocation of attentional resources for reasoning, categorization, and decision making to control behaviour in our environment. Research has suggested that the allocation of attention is sensitive to the frequency of contingency information whether it constitutes a negative, zero or positive relationship. The aim of the present study was to explore the functional neuroanatomical correlates of contingency judgement with different frequencies and whether these are distinct from each other or whether they rely on a common mechanism. Using three contingency tasks within a streaming paradigm (one each for negative, zero, and positive contingency frequencies), we assessed brain activity by means of functional magnetic resonance imaging (fMRI) in 20 participants. Contingency frequency was manipulated between blocks which allowed us to determine the neural correlates of each of the three contingency tasks as well as the common areas of activation. The conjunction of task activation showed activity in left parietal cortices (BA 23, 40) and superior temporal gyrus (BA42). Further, the interaction analysis revealed distinct areas that mainly involve lateral (BA 45) and medial (BA 9) prefrontal cortices in the judgment of negative contingencies compared with positive and zero contingencies. We interpret the finding as evidence that the shared regions may be involved in coding, integration, and updating of associative relations and distinct regions may be involved in the investment of attentional resources to varied degrees in the computation of contingencies to make a judgment.

Characterising the unity and diversity of executive functions in a within-subject fMRI study.

Behavioural studies investigating the relationship between Executive Functions (EFs) demonstrated evidence that different EFs are correlated with each other, but also that they are partially independent from each other. Neuroimaging studies investigating such an interrelationship with respect to the functional neuroanatomical correlates are sparse and have revealed inconsistent findings. To address this question, we created four tasks derived from the same basic paradigm, one each for updating, inhibition, switching, and dual-tasking. We assessed brain activity through functional magnetic resonance imaging (fMRI) in twenty-nine participants while they performed the four EF tasks plus control tasks. For the analysis, we first determined the neural correlates of each EF by subtracting the respective control tasks from the EF tasks. We tested for unity in EF tasks by calculating the conjunction across these four "EF-minus-control" contrasts. This identified common areas including left lateral frontal cortices [middle and superior frontal gyrus (BA 6)], medial frontal cortices (BA 8) as well as parietal cortices [inferior and superior parietal lobules (BA 39/7)]. We also observed areas activated by two or three EF tasks only, such as frontoparietal areas [e.g., SFG (BA8) right inferior parietal lobule (BA 40), left precuneus (BA 7)], and subcortical regions [bilateral thalamus (BA 50)]. Finally, we found areas uniquely activated for updating [bilateral MFG (BA 8) and left supramarginal gyrus (BA 39)], inhibition (left IFG BA 46), and dual-tasking [left postcentral gyrus (BA 40)]. These results demonstrate that the functional neuroanatomical correlates of the four investigated EFs show unity as well as diversity.

Self-perspective in episodic memory after parietal damage and in healthy ageing.

Although there is strong support from functional imaging studies for lateral parietal lobe involvement in episodic memory, patients with damage to these regions do not appear to suffer from severe deficits in this cognitive domain. As such there has been no definitive explanation of this area's precise involvement. Here, we hypothesised that parietal regions play a crucial role in episodic memory - specifically in recollecting details from an egocentric perspective. In order to test this hypothesis systematically, we designed a novel experimental task utilising a head-mounted camera to record images from the participant's perspective, enabling us to evaluate the integrity of memory from the individual's own point of view. In the first study we examined patients with parietal damage and in a second study, using fMRI, we examined young and older healthy participants. Right-hemisphere patients with parietal damage were able to recall information accurately when recollecting what items had been present and where these items had been. However, patients were significantly impaired when attempting to judge from which perspective they had viewed the scenes. Critically, the patient group showed no evidence of impairment on standard tests of episodic and working memory. Examination of healthy participants in the second study utilised multi-voxel pattern analysis on neural activity during the recognition phase of a similar task. This revealed sensitivity to be highest around the angular gyrus of the lateral parietal cortex for our critical comparison - that is, when viewing stimuli that were the same as their egocentric view during encoding versus the identical scene but presented from an alternative angle. Our results provide important evidence that parietal cortex is directly involved in egocentric spatial perspective aspects of episodic memory and demonstrate for the first time a specific deficit in episodic memory in patients with right parietal damage.

Preliminary fMRI findings concerning the influence of 5-HTP on food selection.

OBJECTIVE: This functional magnetic resonance imaging study was designed to observe how physiological brain states can alter food preferences. A primary goal was to observe food-sensitive regions and moreover examine whether 5-HTP intake would activate areas which have been associated with appetite suppression, anorexia, satiety, and weight loss. METHODS AND PROCEDURE: Fourteen healthy male and female participants took part in the study, of which half of them received the supplement 5-HTP and the rest vitamin C (control) on an empty stomach. During the scanning session, they passively observed food (high calories, proteins, carbohydrates) and nonfood movie stimuli. RESULTS: Within the 5-HTP group, a comparison of food and nonfood stimuli showed significant responses that included the limbic system, the basal ganglia, and the prefrontal, temporal, and parietal cortices. For the vitamin C group, activity was mainly located in temporal and occipital regions. Compared to the vitamin C group, the 5-HTP group in response to food showed increased activation on the VMPFC, the DLPFC, limbic, and temporal regions. For the 5-HTP group, activity in response to food high in protein content compared to food high in calories and carbohydrates was located in the limbic system and the right caudomedial OFC, whereas for the vitamin C group, activity was mainly located at the inferior parietal lobes, the anterior cingulate gyri, and the left ventrolateral OFC. Greater responses to carbohydrates and high calorie stimuli in the vitamin C group were located at the right temporal gyrus, the occipital gyrus, the right VLPFC, whereas for the 5-HTP group, activity was observed at the left VMPFC, the parahippocampal gyrus bilaterally, the occipital lobe, and middle temporal gyri. DISCUSSION: In line with the hypotheses, 5-HTP triggered cortical responses associated with healthy body weight as well as cerebral preferences for protein-rich stimuli. The brain's activity is altered by macronutrients rich or deprived in the body. By reading the organisms physiological states and combining them with memory experiences, it constructs behavioral strategies steering an individual toward or in opposition to a particular food.

The man who mistook his neuropsychologist for a popstar: when configural processing fails in acquired prosopagnosia.

We report the case of an individual with acquired prosopagnosia who experiences extreme difficulties in recognizing familiar faces in everyday life despite excellent object recognition skills. Formal testing indicates that he is also severely impaired at remembering pre-experimentally unfamiliar faces and that he takes an extremely long time to identify famous faces and to match unfamiliar faces. Nevertheless, he performs as accurately and quickly as controls at identifying inverted familiar and unfamiliar faces and can recognize famous faces from their external features. He also performs as accurately as controls at recognizing famous faces when fracturing conceals the configural information in the face. He shows evidence of impaired global processing but normal local processing of Navon figures. This case appears to reflect the clearest example yet of an acquired prosopagnosic patient whose familiar face recognition deficit is caused by a severe configural processing deficit in the absence of any problems in featural processing. These preserved featural skills together with apparently intact visual imagery for faces allow him to identify a surprisingly large number of famous faces when unlimited time is available. The theoretical implications of this pattern of performance for understanding the nature of acquired prosopagnosia are discussed.

Understanding grapheme personification: a social synaesthesia?

Much of synaesthesia research focused on colour, but not all cross-domain correspondences reported by synaesthetes are strictly sensory. For example, some synaesthetes personify letters and numbers, in additional to visualizing them in colour. First reported in the 1890s, the phenomenon has been largely ignored by scientists for more than a century with the exception of a few single-case reports. In the present study, we collected detailed self-reports on grapheme personification using a questionnaire, providing us with a comprehensive description of the phenomenology of grapheme personification. Next, we documented the behavioural consequences of personifying graphemes using a congruity paradigm involving a gender judgement task; we also examined whether personification is associated with heightened empathy as measured using Empathy Quotient and found substantial individual differences within our sample. Lastly, we present the first neuroimaging case study of personification, indicating that the precuneus activation previously seen in other synaesthesia studies may be implicated in the process. We propose that frameworks for understanding synaesthesia could be extended into other domains of cognition and that grapheme personification shares more in common with normal cognition than may be readily apparent. This benign form of hyper-mentalizing may provide a unique point of view on one of the most central problems in human cognition - understanding others' state of mind.

Representation of eye position in the human parietal cortex.

Neurons that signal eye position are thought to make a vital contribution to distinguishing real world motion from retinal motion caused by eye movements, but relatively little is known about such neurons in the human brain. Here we present data from functional MRI experiments that are consistent with the existence of neurons sensitive to eye position in darkness in the human posterior parietal cortex. We used the enhanced sensitivity of multivoxel pattern analysis (MVPA) techniques, combined with a searchlight paradigm, to isolate brain regions sensitive to direction of gaze. During data acquisition, participants were cued to direct their gaze to the left or right for sustained periods as part of a block-design paradigm. Following the exclusion of saccade-related activity from the data, the multivariate analysis showed sensitivity to tonic eye position in two localized posterior parietal regions, namely the dorsal precuneus and, more weakly, the posterior aspect of the intraparietal sulcus. Sensitivity to eye position was also seen in anterior portions of the occipital cortex. The observed sensitivity of visual cortical neurons to eye position, even in the total absence of visual stimulation, is possibly a result of feedback from posterior parietal regions that receive eye position signals and explicitly encode direction of gaze.

Static representations of speed and their neural correlates in human area MT/V5.

Studies have shown that cortical area MT/V5 is activated by visual motion as well as illusory motion, implied motion in static images, or motion imagery. Cells within these areas are additionally tuned for speed and exhibit different responses depending on the actual speed of an object. In this study, we investigate the relationship between perceived speed as represented within static images and the patterns of activity observed in MT/V5. Consistent with other studies, we show robust responses in MT/V5 to implied motion. In addition, our results show an increase in the blood-oxygen level dependent response consistent with the increased speed information inherent within the images. In the absence of any real physical motion, the data illustrate the intricate manner in which top-down activity influences visual cortical activity.

Attentional modulation in the human visual cortex: the time-course of the BOLD response and its implications.

Throughout the visual areas of the brain, the sensory response to a stimulus is enhanced by attending to the stimulus. Neurophysiological studies in primates show that such enhancement is marked in posterior parietal cortex and some anterior occipital areas, but much more modest in the earliest processing stages, such as the primary visual cortex (V1). In contrast, human fMRI studies show large and robust attentional modulation in all visual areas, including V1. We investigate the possibility that, in the case of fMRI, the BOLD (blood oxygen level dependent) response may be increased not only by local attention-related increases in neural activity, but also by local blood-flow increases caused by remote control systems that anticipate an impending need for oxygen at the attended location. Such changes could be much more rapid than the rather slow response to oxygenation change that typifies the BOLD response. We have employed a paradigm that isolates the component of the BOLD response due to attentional modulation and the component due to the mere presence of a visual stimulus. The results show that the temporal profiles of the BOLD responses in human V1 to the onset of a stimulus and to the onset of attention are extremely similar. The time-course of the attention-related BOLD response is not consistent with the action of remote, anticipatory control mechanisms and suggests that the modulatory effect of attention seen in human V1 with fMRI probably reflects genuine changes in local neural activity that are considerably larger than in non-human primates.

Negative BOLD in the visual cortex: evidence against blood stealing.

The positive BOLD (blood oxygen level-dependent) response elicited in human visual cortex by a localized visual stimulus is accompanied by a reduction in the BOLD response in regions of the visual cortex that represent unstimulated locations in the visual field. We have suggested previously that this negative BOLD reflects attention-related suppression of neural activity, but it might also be explained in terms of "blood stealing," i.e., hemodynamic changes that have no neural correlate. We distinguish two possible hemodynamic effects of this type: (1). blood flow reduction caused by locally reduced pressure in vessels that share their blood supply with nearby dilated vessels; and (2). blood flow reduction caused by active constriction of vessels under neural control. The first is ruled out as an explanation of negative BOLD by showing that a visual stimulus that stimulates primary visual cortex in one hemisphere can cause extensive suppression in the other hemisphere i.e., it is not a local phenomenon. Negative BOLD most likely reflects suppression of neural activity, but could also reflect an active blood flow control system.

Surround modulation measured with functional MRI in the human visual cortex.

Visual context profoundly influences 1) the responses of mammalian visual neurons and 2) the perceptual sensitivity of human observers to localized visual stimuli. We present data from functional MRI studies demonstrating contextual modulation in the human visual cortex. Subjects viewed a circular grating patch that was continuously present. A surround grating was added in an ON-OFF block design to reveal its effect on the central region. Stimulus-correlated activation was quantified and visualized on a flattened map of the occipital gray matter. Modulation was measured in a region of interest activated by the central grating alone. The observed effects were predominantly suppressive, consistent with the effects typically found in single neurons and perception. Suppression was greatest when the surround and center had the same orientation and was reduced or absent when it was orthogonal. When spatial phase was manipulated, suppression was greatest for in-phase center/surround gratings and much reduced or reversed (facilitation) for opposite-phase stimuli. With eccentric stimulus presentation, suppression was reduced and facilitation became more common. The findings provide a direct demonstration of the existence of powerful and stimulus-specific surround effects in human visual cortex.

Task-related changes in cortical synchronization are spatially coincident with the hemodynamic response.

Using group functional Magnetic Resonance Imaging (fMRI) and group Magnetoencephalography (MEG) we studied two cognitive paradigms: A language task involving covert letter fluency and a visual task involving biological motion direction discrimination. The MEG data were analyzed using an adaptive beam-former technique known as Synthetic Aperture Magnetometry (SAM), which provides continuous 3-D images of cortical power changes. These images were spatially normalized and averaged across subjects to provide a group SAM image in the same template space as the group fMRI data. The results show that frequency-specific, task-related changes in cortical synchronization, detected using MEG, match those areas of the brain showing an evoked cortical hemodynamic response with fMRI. The majority of these changes were event-related desynchronizations (ERDs) in the 5-10 Hz and 15-25 Hz frequency ranges. Our study demonstrates how SAM, spatial normalization, and intersubject averaging enable group MEG studies to be performed. SAM analysis also allows the MEG experiment to have exactly the same task design as the corresponding fMRI experiment. This new analysis framework represents an important advance in the use of MEG as a cognitive neuroimaging technique and also allows mutual cross-validation with fMRI.

Role of retinal afferents in regulating growth and shape of the lateral geniculate nucleus.

Segregated binocular maps in the dorsal lateral geniculate nucleus (LGN) develop from a stage where they initially overlap. Sophisticated computational models have been used to describe the dynamics of three-dimensional LGN shape changes that play a role in segregation. These models have revealed specific nuclear growth vectors associated with the process of ocular segregation in the LGN (Williams and Jeffery [2001] J Comp Neurol 430:332-342.). In this study, we use similar techniques to determine whether retinal innervation contributes to the dynamics of shape maturation in the ferret LGN. In this animal, 90% of the retinal innervation of the mature LGN comes from the contralateral eye. If one eye is removed before segregation, the projection from the remaining eye remains diffuse and nuclear growth is stunted. Here, we quantify this effect and show that removing the contralateral projection before segregation has a profound impact on LGN size but changes its ultimate shape by only 12%. The impact on shape on the other side of the brain where the ipsilateral projection is removed, which accounts for only 10% of its innervation in maturity, is less than 2%. Hence, retinal innervation plays a minor role in determining mature LGN shape. Although in both hemispheres, the ultimate shape of the nucleus is close to normal, removal of the larger projection disrupts normal growth vectors, with almost none being present in the 5 days after enucleation, when the normal nucleus expands markedly. Hence, the effect of enucleation is to delay shape maturation. Growth vectors absent after removal of the smaller projection are mainly confined to those in what would be the binocular region.