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The orbitofrontal cortex (OFC) processes the occurrence or omission of anticipated rewards, but clinical evidence suggests that it might serve as a generic outcome monitoring system, independent of tangible reward. In this positron emission tomography (PET) study, normal human subjects performed a series of tasks in which they simply had to predict behind which one of two colored rectangles a drawing of an object was hidden. While all tasks involved anticipation in that they had an expectation phase between the subject's prediction and the presentation of the outcome, they varied with regards to the uncertainty of outcome. No comment on the correctness of the prediction, no record of ongoing performance, and no reward, not even a score, was provided. Nonetheless, we found strong activation of the OFC: in comparison with a baseline task, the left anterior medial OFC showed activation in all conditions, indicating a basic role in anticipation; the left posterior OFC was activated in all tasks with some uncertainty of outcome, suggesting a role in the monitoring of outcomes; the right medial OFC showed activation exclusively during guessing. The data indicate a generic role of the human OFC, with some topical specificity, in the generation of hypotheses and processing of outcomes, independent of the presence of explicit reward.
Neuropsychiatric symptoms seen in Alzheimer's disease (AD) are not simply a consequence of neurodegeneration, but probably result from differential neurotransmitter alterations, which some patients are more at risk of than others. Therefore, the hypothesis of this study is that an imbalance between the cholinergic and serotonergic systems is related to cognitive symptoms and psychological syndromes of dementia (BPSD) in patients with AD. Cholinergic and serotonergic functions were assessed in post-mortem frontal and temporal cortex from 22 AD patients who had been prospectively assessed with the Mini-Mental State examination (MMSE) for cognitive impairment and with the Present Behavioral Examination (PBE) for BPSD including aggressive behavior, overactivity, depression and psychosis. Not only cholinergic deficits, but also the cholinacetyltransferase/serotonin ratio significantly correlated with final MMSE score both in frontal and temporal cortex. In addition, decreases in cholinergic function correlated with the aggressive behavior factor, supporting a dual role for the cholinergic system in cognitive and non-cognitive disturbances associated to AD. The serotonergic system showed a significant correlation with overactivity and psychosis. The ratio of serotonin to acetylcholinesterase levels was also correlated with the psychotic factor at least in women. It is concluded that an imbalance between cholinergic-serotonergic systems may be responsible for the cognitive impairment associated to AD. Moreover, the major findings of this study are the relationships between neurochemical markers of both cholinergic and serotonergic systems and non-cognitive behavioral disturbances in patients with dementia.
It has been proposed that behavior is influenced by representations of different types of knowledge: action representations, event knowledge, attitudes and stereotypes. Attitudes (representations of a concept or object and its emotional evaluation) allow us to respond quickly to a given stimulus. In this study, we explored the representation and inhibition of attitudes. We show that right dorsolateral prefrontal cortex mediates negative attitudes whereas left ventrolateral prefrontal cortex mediates positive attitudes. Parahippocampal regions and amygdala mediate evaluative processing. Furthermore, anxiety modulates right dorsolateral prefrontal activation during negative attitude processing. Inhibition of negative attitudes activates left orbitofrontal cortex: a region that when damaged is associated with socially inappropriate behavior in patients. Inhibition of positive attitudes activates a brain system involving right inferior frontal gyrus and bilateral anterior cingulate. Thus, we show that there are dissociable networks for the representation and inhibition of attitudes.
The present study sought to assess neural correlates of implicit identification of objects by means of fMRI, using tasks that require matching of the physical properties of objects. Behavioural data suggests that there is automatic access to object identity when observers attend to a physical property of the form of an object (e.g. the object's orientation) and no evidence for semantic processing when subjects attend to colour. We evaluated whether, in addition to neural areas associated with decisions to specific perceptual properties, areas associated with access to semantic information were activated when tasks demanded processing of the global configuration of pictures. We used two perceptual matching tasks based on the global orientation or on the colour of line drawings. Our results confirmed behavioural data. Activations in the inferior occipital cortex, fusiform and inferior temporal gyri in both tasks (orientation and colour) account for perceptual and structural processing involved in each task. In contrast, activations in the posterior and medial parts of the fusiform gyrus, shown to be involved in explicit semantic judgements, were more pronounced in the orientation-matching task, suggesting that semantic information from the pictures is processed in an implicit way even when not required by the task. Thus, this study suggests that cortical regions usually involved in explicit semantic processing are also activated when implicit processing of objects occurs.
Asymmetries in human facial expressions have long been documented and traditionally interpreted as evidence of brain laterality in emotional behavior. Recent findings in nonhuman primates suggest that this hemispheric specialization for emotional behavior may have precursors in primate evolution. In this study, we present the first data collected on our closest living relative, the chimpanzee. Objective measures (hemimouth length and area) and subjective measures (human judgements of chimeric stimuli) indicate that chimpanzees' facial expressions are asymmetric, with a greater involvement of the left side of the face in the production of emotional responses. No effect of expression type (positive versus negative) on facial asymmetry was found. Thus, chimpanzees, like humans and some other nonhuman primates, show a right hemisphere specialization for facial expression of emotions.
Induced gamma-band response (iGBR) has been linked to coherent perception of images and is thought to represent the synchronisation of neuronal populations mediating binding of elements composing the image and the comparisons with memory for proper recognition. This study uses fragmented images with intracranial electroencephalography to investigate the precise spatio-temporal dynamic of iGBR elicited by the recognition of objects presented for the first time and 24h later. Results show an increased iGBR at recognition in regions involved in bottom-up processes such as the cuneus and the lateral occipital complex. Top-down facilitation involved the lingual gyrus, the precuneus and the superior parietal lobule when images were presented for the first time. Twenty-four hours later, top-down facilitation was mediated by frontal areas involved in retrieval from episodic memory. This study showed that the classically reported iGBR is related to object recognition and that top-down processes vary according to task demand.
The current rapid event-related fMRI study used optional parasitic-gap constructions, such as [Which paper] did the tired student submit [(gap)--] after reviewing [(p-gap)--/it]?, to test 3 potential roles for Broca's area in sentence processing. These 3 functional options are: I. any intra-sentential Dependency relation activates Broca's area. II. This region specifically processes syntactic Displacement or movement. III. Broca's area handles any dependency relation, as long as it is predictable at an early stage of processing. Broca's area was only activated by the contrast that tested predictability within BA 45, as determined by its overlap with cytoarchitectonic probability maps. These results imply that an alternative or modified functional account of Broca's area, from those presently available, is required. Constraints on either a displacement account to movements that are not parasitic or a Working Memory one to predicted dependencies that cross verbal arguments or noun phrases would achieve the necessary consistency. Further, the results from the minimal contrasts investigating displacement and dependency have implications to potential language regions outside of Broca's area. The minimal contrast investigating displacement activated the left anterior Middle Temporal Gyrus, which has more recently been claimed to play a role in syntactic operations.
Awareness of deficits after brain injury represents a significant clinical and theoretical challenge, but relatively little is known about the neuroanatomical correlates of specific types of deficit awareness. We examined the awareness correlates of left versus right prefrontal cortex lesions in comparison to left and right posterior lesions including two types of awareness measures--metacognitive and online error monitoring. Frontal lobe frontal lesion patients exhibited impaired metacognitive awareness and also showed deficits in monitoring errors as they occurred. In addition, frontal lobe lesion patients also showed reduced autonomic response to aware errors. Online and metacognitive awareness were not, however, significantly correlated, suggesting that distinct neuroanatomical systems may underpin these two types of awareness deficit. We hypothesize that while metacognitive awareness depends on both left and right frontal regions, accurate moment-to-moment processing of errors depends more on the right than on the left prefrontal cortex.
Patients with visual extinction following right-hemisphere damage sometimes see and sometimes miss stimuli in the left visual field, particularly when stimuli are presented simultaneously to both visual fields. Awareness of left visual field stimuli is associated with increased activity in bilateral parietal and frontal cortex. However, it is unknown why patients see or miss these stimuli. Previous neuroimaging studies in healthy adults show that prestimulus activity biases perceptual decisions, and biases in visual perception can be attributed to fluctuations in prestimulus activity in task relevant brain regions. Here, we used functional MRI to investigate whether prestimulus activity affected perception in the context of visual extinction following stroke. We measured prestimulus activity in stimulus-responsive cortical areas during an extinction paradigm in a patient with unilateral right parietal damage and visual extinction. This allowed us to compare prestimulus activity on physically identical bilateral trials that either did or did not lead to visual extinction. We found significantly increased activity prior to stimulus presentation in two areas that were also activated by visual stimulation: the left calcarine sulcus and right occipital inferior cortex. Using dynamic causal modelling (DCM) we found that both these differences in prestimulus activity and stimulus evoked responses could be explained by enhanced effective connectivity within and between visual areas, prior to stimulus presentation. Thus, we provide evidence for the idea that differences in ongoing neural activity in visually responsive areas prior to stimulus onset affect awareness in visual extinction, and that these differences are mediated by fluctuations in extrinsic and intrinsic connectivity.
Bilingual studies have shown that brain activities for first (L1) and second (L2) languages are influenced by L2 proficiency. Does proficiency with a second musical system (M2) influence bimusical brains in a manner similar to that of bilingual brains? Our magnetoencephalography study assessed the influence of M2 proficiency on the spatial, strength, and temporal properties of brain activity in a musical syntactic-processing task (i.e., tonal processing) involving first (M1) and second (M2) music systems. Two bimusical groups, differing in M2 proficiency (high, low), listened to melodies from both their M1 and M2 musical cultures. All melodies ended with a tonally consistent or inconsistent tone. In both groups, tonal deviations in both M1 and M2 elicited magnetic early right anterior negativities (mERANs) that were generated from brain areas around the inferior frontal gyrus (IFG). We also analyzed the dipole locations, dipole strengths, and peak latencies of mERAN. Results revealed: (a) the distances between dipole locations for M1 and M2 were shorter in the M2 high-proficiency group than in the M2 low-proficiency group; (b) the dipole strengths were greater in the high than the low group; (c) the peak latencies of M2 were shorter in the high than low group. The dipole location results were consistent with those from bilingual studies in that the distances between the (left) IFG peak activations for L1 and L2 syntactic processing shortened as L2 proficiency increased. The parallel results for bimusicals and bilinguals suggest that the functional changes induced by proficiency in a second (linguistic or musical) system are defined by domain-general neural constraints.
The present study addressed an outstanding issue regarding feature binding in working memory (WM): whether this function engages specific resources relative to those required to process individual features. We investigated the brain regions supporting the encoding and maintenance of features and bindings in a change detection task, in which 22 healthy young volunteers remembered visual arrays of abstract shapes, colors or shape-color bindings while undergoing fMRI. After an unfilled delay they saw a second array and judged whether the features or combination of features presented across the two arrays were the same or different. Temporary retention of feature bindings was found to involve additional cortical regions compared with retaining single features, regardless of whether the number of objects or the number of features differed between feature-only and binding conditions. This binding-specific activation is consistent with the involvement of different neural generators that collectively support visual temporary memory for features and for feature bindings. Regions within the parietal, temporal and occipital cortex, but not within the prefrontal cortex or the medial temporal lobe, appear to support the integrated object binding function investigated in this study. Our findings suggest that both individual features and their binding within integrated objects are used to represent complex objects in WM.
During visual perception, automatic bottom-up and controlled top-down processes occur simultaneously and interact in a complex way, making them difficult to isolate and characterize. In rare neurological conditions, such a dissociation can be achieved more easily. In the present work, we studied a patient (AC) with a posterior lesion of the corpus callosum (CC), using a combination of behavioural, structural MRI and high-density scalp EEG measures. Given the complete disruption of the posterior half of the CC, we speculated that inter-hemispheric transfer of visual information was only possible through top-down mobilization across the preserved anterior segment of the CC. We designed a matching-to-sample visual task during which this patient was randomly presented with two successive numerical targets (T1 and T2) flashed with either a short or a long stimulus-onset asynchrony (SOA), each presented within one visual hemifield (HF). Intra-hemispheric processing of visual stimuli was essentially preserved. In sharp contrast, patient's performance was massively impaired during inter-HFs trials with a short-SOA, confirming the lack of fast inter-hemispheric transfer. Crucially, patient AC spontaneously improved his performance in inter-HFs trials with a long-SOA. This behavioral improvement was correlated with a mid-frontal ERP effect occurring during the T1-T2 interval, concomitant with an increase of functional connectivity of this region with distant areas including occipital regions. These results put to light a slow, non-automatic, and frontally mediated route of inter-hemispheric transfer dependent on top-down control.
Memories of real and imagined events are qualitatively distinct, and therefore may be supported by different neural mechanisms. In the present study, we tested whether brain regions are differentially activated during source discriminations of perceived versus imagined events. During the encoding phase, subjects perceived and imagined images of objects in response to a cue word. Then, at test, they made judgments about whether old and new cue words corresponded to items that were previously perceived or imagined, or if they were new. The results demonstrated that the left lateral posterior parietal cortex and dorsolateral prefrontal cortex were significantly more active during source attributions of perceived compared to imagined events. In addition, activity in these regions was associated with successful item memory (hits>correct rejections) for perceived, but not imagined events. These findings of a source-based dissociation of successful retrieval activity have important implications regarding theories of parietal contributions to recognition memory.
Anhedonia is associated with reward-processing deficits of the dopamine system, which may increase the risk of depression. Nevertheless, few previous studies have examined the influence of hedonic tone on event-related potential (ERP) measures of reward processing in major depressive disorder. A simple gambling task was used to elicit feedback negativity (FN), an ERP component elicited by feedback indicating gain versus loss, in 27 patients with major depression and 27 healthy participants. We found that participants with depression were characterized by reduced FN responses, especially towards monetary gains, but not losses, compared with healthy individuals. In addition, the amplitude of FN to gain feedback in participants with depression was related to anhedonia severity and depressive symptoms. These findings indicate an association between low hedonic capacity and reduction in FN. As a neural measure of reward sensitivity, FN may be generated in part by reward-related activity.
Amnesia and linguistic deficits that are associated with thalamic damage have attracted the attention of researchers interested in identifying the neural networks involved in memory and language. The Papez circuit, which is composed of the hippocampus, mammillary body and anterior thalamic nuclei, was first proposed to be critical for memory. However, subsequently, the roles of the neural circuit consisting of the rhinal/parahippocampal cortices and the mediodorsal thalamic nuclei became evident. The ventral lateral nuclei or its adjacent structures have been found to be involved in semantic processing, but the specific neural circuits dedicated to language functions have not been identified. Anterior thalamic infarcts, which affect very circumscribed regions of the ventral anterior portion of the thalamus, often cause paradoxically prominent memory and language deficits. We conducted tractography analyses in 6 patients with left anterior thalamic infarcts to identify neural connections or circuits in which disruptions are associated with memory and language deficits in this condition. The current study demonstrated that the mammillothalamic tract, which connects the mammillary body with the anterior thalamic nuclei, and the anterior and inferior thalamic peduncles, which contain neural fibers that extend from several thalamic nuclei to the anterior temporal, medial temporal and frontal cortices, are disrupted in anterior thalamic infarction. These extensive thalamo-cortical disconnections appear to be due to the dissection of the neural fibers that penetrate the ventral anterior nucleus of the thalamus. Our results suggest the following: (1) amnesia that is associated with anterior thalamic infarction is best interpreted in the context of dual/multiple-system theories of memory/amnesia that posit that multiple neural circuits connecting the anterior and mediodorsal thalamic nuclei with the hippocampus and rhinal/parahippocampal cortices work in concert to support memory function; and (2) the semantic deficits observed in this syndrome may be associated with thalamo-anterior temporal and thalamo-lateral frontal disconnections.
Hyperkinetic perseveration (HKP) refers to perseverative repetition of rudimentary motor output. Although HKP is known to be associated with brain injuries and certain neurodegenerative disorders (primarily those involving the frontal lobes and the basal ganglia), an increased tendency to exhibit HKP is also commonly associated with apparently normal aging (i.e., in the absence of known neuropathology). The purpose of the present study was to examine anomalies in brain functioning associated with HKP tendencies in a non-injured brain.
The integration of auditory feedback with vocal motor output is important for the control of voice fundamental frequency (F0). We used a pitch-shift paradigm where subjects respond to an alteration, or shift, of voice pitch auditory feedback with a reflexive change in F0. We presented varying magnitudes of pitch shifted auditory feedback to subjects during vocalization and passive listening and measured event related potentials (ERPs) to the feedback shifts. Shifts were delivered at +100 and +400 cents (200 ms duration). The ERP data were modeled with dynamic causal modeling (DCM) techniques where the effective connectivity between the superior temporal gyrus (STG), inferior frontal gyrus and premotor areas were tested. We compared three main factors: the effect of intrinsic STG connectivity, STG modulation across hemispheres and the specific effect of hemisphere. A Bayesian model selection procedure was used to make inference about model families. Results suggest that both intrinsic STG and left to right STG connections are important in the identification of self-voice error and sensory motor integration. We identified differences in left-to-right STG connections between 100 cent and 400 cent shift conditions suggesting that self- and non-self-voice error are processed differently in the left and right hemisphere. These results also highlight the potential of DCM modeling of ERP responses to characterize specific network properties of forward models of voice control.
Music listening involves using previously internalized regularities to process incoming musical structures. A condition known as congenital amusia is characterized by musical difficulties, notably in the detection of gross musical violations. However, there has been increasing evidence that individuals with the disorder show preserved musical ability when probed using implicit methods. To further characterize the degree to which amusic individuals show evidence of latent sensitivity to musical structure, particularly in the context of stimuli that are ecologically valid, electrophysiological recordings were taken from a sample of amusic and control participants as they listened to real melodies. To encourage them to pay attention to the music, participants were asked to detect occasional notes in a different timbre. Using a computational model of auditory expectation to identify points of varying levels of expectedness in these melodies (in units of information content (IC), a measure which has an inverse relationship with probability), ERP analysis investigated the extent to which the amusic brain differs from that of controls when processing notes of high IC (low probability) as compared to low IC ones (high probability). The data revealed a novel effect that was highly comparable in both groups: Notes with high IC reliably elicited a delayed P2 component relative to notes with low IC, suggesting that amusic individuals, like controls, found these notes more difficult to evaluate. However, notes with high IC were also characterized by an early frontal negativity in controls that was attenuated in amusic individuals. A correlation of this early negative effect with the ability to make accurate note expectedness judgments (previous data collected from a subset of the current sample) was shown to be present in typical individuals but compromised in individuals with amusia: a finding in line with evidence of a close relationship between the amplitude of such a response and explicit knowledge of musical deviance.
The planum temporale is a highly lateralized cortical region, located within Wernicke's area, which is thought to be involved in auditory processing, phonological processing, and language. Research has linked abnormal morphology of the planum temporale to developmental dyslexia, although results have varied in large part due to methodological inconsistencies in the literature. This study examined the asymmetry of the planum temporale in 29 children who met criteria for dyslexia and 26 children whose reading was unimpaired. Leftward asymmetry of the planum temporale was found in the total sample and this leftward asymmetry was significantly reduced in children with dyslexia. This reduced leftward asymmetry in children with dyslexia was due to a planum temporale that is larger in the right hemisphere. This study lends support to the idea that planum temporale asymmetry is altered in children with developmental dyslexia.
The perception of tools vs. other objects has been shown to activate the left premotor and somatosensory cortex, which represents object affordance associated with tool manipulability (Proverbio, Adorni, & D'Aniello, 2011). The question of whether hemispheric asymmetry depends on right hand use or is linked to a hemispheric functional specialization for fine-grained precision movement is unclear. Thus, in this paper, ERPs were recorded from 128 sites in response to the visual presentation of bidimensional (2D) pictures depicting unimanual (e.g., a hammer) and bimanual (e.g., a handlebar) tools (Study 1). Central N2 and prefrontal N400 components were much larger for bimanual than unimanual tools (over the left hemisphere for N400). SwLORETAs performed for both components showed at first the activation of the left parietal cortex (BA39) and then of the right homologous (BA40) one, for both grips but stronger for the bimanual coordination. At all times and for both grips, the left premotor cortex (BA6) was involved in coding action affordance, while only unimanual tools activated the left postcentral gyrus (BA3). In Study 2, unimanual tools were presented with an orientation congruent (standard) or incongruent to their interaction with the right hand (rotated), to manipulate affordance's quality. Standard objects elicited much larger ERP responses (namely: N1, N2, N400) than rotated tools (over the left hemisphere for N400). At the earliest stage (190-270 ms) the significant intracranial sources were of visual nature (mainly the contralateral precuneus). Regions representing motor information were not involved. Rotated tools induced a smaller activation in the STS and parahippocampal regions (possibly coding affordable biological motion and the spatial aspects of hand/object interaction), whereas rotated tools activated to a greater extent the dorsolateral prefrontal cortex (DLPF, BA9). In the later time window standard objects activated the left BA6 and the right BA40 more than rotated objects. Overall, these data suggest that viewing tools automatically activates mental representations associated with their manipulation. The left premotor cortex was found to be involved with any kind of object and grip, as early as 200 ms post-stimulus, thus supporting the hypothesis of a LH asymmetry in the neural representation of grasping, within this region. The right supramarginal gyrus was also found to be crucially involved later in time.
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