Neuronal correlates of familiarity-driven decisions in artificial grammar learning

It has been proposed on the basis of behavioural data that grammaticality judgments in implicit artificial grammar learning paradigms are largely driven by priming based on fragment familiarity. A prediction that follows from this account is that neural deactivation, a common correlate of repetition priming, should be observed for grammatical compared to ungrammatical stimuli. We conducted an event-related fMRI study to investigate neuronal correlates of such fragment-based priming. In a study phase, participants performed a short-term memory task on a series of strings of pseudofont characters. Scanning was performed in a subsequent test phase in which participants classified new strings as either grammatical or ungrammatical. Test strings differed systematically from training strings in terms of exemplar and fragment similarity. Behaviourally, participants classified strings as grammatical based on fragment familiarity. Differential activity was evident during string classification as reduced activity in left lateral occipital complex and bilateral lingual gyri for strings with high fragment familiarity compared to strings with low fragment familiarity. Thus, consistent with the hypothesis, neuronal facilitation in extrastriate occipital regions may constitute one basis of implicit grammaticality decisions based on fragment priming.

Effects of cholinergic enhancement on conditioning-related responses in human auditory cortex

It has previously been shown that cholinergic blockade attenuates conditioning-related neuronal responses in human auditory cortex. The present study was conducted to investigate the effect of cholinergic enhancement on such experience-dependent cortical responses. The cholinesterase inhibitor physostigmine, or a placebo control, were continuously infused into healthy young volunteers, during differential aversive conditioning whilst brain activity was measured using event-related functional magnetic resonance imaging (fMRI). Volunteers were presented with two tones, one of which (CS+) was conditioned by pairing with an electrical shock whereas the other was always presented without the shock (CS-). Conditioning-related activations, expressed as an enhanced blood oxygenation level dependent (BOLD) response to the salient CS+, were evident in left auditory cortex under placebo but not under physostigmine. This absence of conditioning-related activations under physostigmine was due to enhanced responses to the CS- under physostigmine as compared to placebo. We suggest that an overactive cholinergic system leads to increased processing of behaviourally irrelevant stimuli and thus attenuates differential conditioning-related cortical activations.

Neural response to emotional faces with and without awareness: event-related fMRI in a parietal patient with visual extinction and spatial neglect

This study examined whether differential neural responses are evoked by emotional stimuli with and without conscious perception, in a patient with visual neglect and extinction. Stimuli were briefly shown in either right, left, or both fields during event-related fMRI. On bilateral trials, either a fearful or neutral left face appeared with a right house, and it could either be extinguished from awareness or perceived. Seen faces in left visual field (LVF) activated primary visual cortex in the damaged right-hemisphere and bilateral fusiform gyri. Extinguished left faces increased activity in striate and extrastriate cortex, compared with right houses only. Critically, fearful faces activated the left amygdala and extrastriate cortex both when seen and when extinguished; as well as bilateral orbitofrontal and intact right superior parietal areas. Comparison of perceived versus extinguished faces revealed no difference in amygdala for fearful faces. Conscious perception increased activity in fusiform, parietal and prefrontal areas of the left-hemisphere, irrespective of emotional expression; while a differential emotional response to fearful faces occurring specifically with awareness was found in bilateral parietal, temporal, and frontal areas. These results demonstrate that amygdala and orbitofrontal cortex can be activated by emotional stimuli even without awareness after parietal damage; and that substantial unconscious residual processing can occur within spared brain areas well beyond visual cortex, despite neglect and extinction.

Emotion, cognition, and behavior

Emotion is central to the quality and range of everyday human experience. The neurobiological substrates of human emotion are now attracting increasing interest within the neurosciences motivated, to a considerable extent, by advances in functional neuroimaging techniques. An emerging theme is the question of how emotion interacts with and influences other domains of cognition, in particular attention, memory, and reasoning. The psychological consequences and mechanisms underlying the emotional modulation of cognition provide the focus of this article.

Emotion, cognition, and behavior

Emotion is central to the quality and range of everyday human experience. The neurobiological substrates of human emotion are now attracting increasing interest within the neurosciences motivated, to a considerable extent, by advances in functional neuroimaging techniques. An emerging theme is the question of how emotion interacts with and influences other domains of cognition, in particular attention, memory, and reasoning. The psychological consequences and mechanisms underlying the emotional modulation of cognition provide the focus of this article.

Functional magnetic resonance imaging of proactive interference during spoken cued recall

Though lesions to frontal cortex can increase susceptibility to interference from previously established but irrelevant memories ("proactive interference"), the specific regions underlying this problem are difficult to determine because the lesions are typically large and heterogeneous. We used event-related functional magnetic resonance imaging to investigate proactive interference in healthy volunteers performing an "AB-AC" paired-associate cued-recall paradigm. At Study, participants intentionally encoded semantically related visual word pairs, which were changed three times (high interference), repeated three times (low interference), or presented only once. At Test, participants were presented with the first word of each pair and attempted to recall its most recent associate from the Study phase. To overcome the problem of image artifacts caused by speech-related head motion, we cued speech during a gap between image acquisitions. Regions in left inferior frontal cortex and bilateral frontopolar cortex showed interference effects during both Study and Test. The pattern of responses in these regions differed, however. Left inferior frontal regions showed mainly reduced responses associated with low interference, whereas frontopolar regions showed mainly increased responses associated with high interference. When incorrect as well as correct trials were analyzed at Test, additional activation associated with high interference was observed in right dorsolateral prefrontal cortex. These data suggest that distinct regions within prefrontal cortex subserve different functions in the presence of proactive interference during cued recall.

Human amygdala responses to fearful eyes

Fearful facial expressions evoke increased neural responses in human amygdala. We used event-related fMRI to investigate whether eye or mouth components of a fearful face are critical in evoking this increased amygdala activity. In addition to prototypical fearful (FF) and neutral (NN) faces, subjects viewed two types of chimerical face: fearful eyes combined with a neutral mouth (FN), and neutral eyes combined with a fearful mouth (NF). FE faces evoked specific responses in left anterior amygdala. FN faces evoked responses in bilateral posterior amygdala and superior colliculus. Responses in right amygdala, superior colliculus, and pulvinar exhibited significant time x condition interactions with respect to faces with fearful eyes (FF, FN) vs neutral eyes (NF, NN). These data indicate that fearful eyes alone are sufficient to evoke increased amygdala activity. In addition, however, left amygdala displayed discriminatory responses to fearful eyes in different configural contexts (i.e., in FF and FN faces). These results suggest, therefore, that human amygdala responds to both feature-specific and configural aspects of fearful facial expressions.

An fMRI study of intentional and unintentional (embarrassing) violations of social norms

The aim of this investigation was to identify neural systems supporting the processing of intentional and unintentional transgressions of social norms. Using event-related fMRI, we addressed this question by comparing neural responses to stories describing normal behaviour, embarrassing situations or violations of social norms. Processing transgressions of social norms involved systems previously reported to play a role in representing the mental states of others, namely medial prefrontal and temporal regions. In addition, the processing of transgressions of social norms involved systems previously found to respond to aversive emotional expressions (in particular angry expressions); namely lateral orbitofrontal cortex (Brodmann area 47) and medial prefrontal cortex. The observed responses were similar for both intentional and unintentional social norm violations, albeit more pronounced for the intentional norm violations. These data suggest that social behavioural problems in patients with frontal lobe lesions or fronto-temporal dementia may be a consequence of dysfunction within the systems identified in light of their possible role in processing whether particular social behaviours are, or are not, appropriate.

Adaptive anterior hippocampal responses to oddball stimuli

An efficient memory system requires the ability to detect and preferentially encode novel stimuli. Human electrophysiological recordings demonstrate differential hippocampal responses to novel vs. familiar stimuli, as well as to oddball stimuli. Although functional imaging experiments of novelty detection have demonstrated hippocampal activation, oddball-evoked hippocampal activation has not been demonstrated. Here we use event-related functional magnetic resonance imaging (fMRI) to measure hippocampal responses to three types of oddball words: perceptual, semantic, and emotional. We demonstrate left anterior hippocampal sensitivity to all three oddball types, with adaptation of responses across multiple oddball presentations. This adaptive hippocampal oddball response was not modulated by depth of processing, suggesting a high degree of automaticity in the underlying process. However, an interaction with depth of encoding for semantic oddballs was evident in a more lateral left anterior hippocampal region. We conclude that the hippocampal response to oddballs demonstrates a second-order novelty effect, being sensitive to the "novelty of novelty" of oddball stimuli. The data provide support for a more general theory that a function of the anterior hippocampus is to register mismatches between expectation and experience.

Multiple levels of visual object constancy revealed by event-related fMRI of repetition priming

We conducted two event-related functional magnetic resonance imaging (fMRI) experiments to investigate the neural substrates of visual object recognition in humans. We used a repetition-priming method with visual stimuli recurring at unpredictable intervals, either with the same appearance or with changes in size, viewpoint or exemplar. Lateral occipital and posterior inferior temporal cortex showed lower activity for repetitions of both real and non-sense objects; fusiform and left inferior frontal regions showed decreases for repetitions of only real objects. Repetition of different exemplars with the same name affected only the left inferior frontal cortex. Crucially, priming-induced decreases in activity of the right fusiform cortex depended on whether the three-dimensional objects were repeated with the same viewpoint, regardless of whether retinal image size changed; left fusiform decreases were independent of both viewpoint and size. These data show that dissociable subsystems in ventral visual cortex maintain distinct view-dependent and view-invariant object representations.

Automatic and intentional brain responses during evaluation of trustworthiness of faces

Successful social interaction partly depends on appraisal of others from their facial appearance. A critical aspect of this appraisal relates to whether we consider others to be trustworthy. We determined the neural basis for such trustworthiness judgments using event-related functional magnetic resonance imaging. Subjects viewed faces and assessed either trustworthiness or age. In a parametric factorial design, trustworthiness ratings were correlated with BOLD signal change to reveal task-independent increased activity in bilateral amygdala and right insula in response to faces judged untrustworthy. Right superior temporal sulcus (STS) showed enhanced signal change during explicit trustworthiness judgments alone. The findings extend a proposed model of social cognition by highlighting a functional dissociation between automatic engagement of amygdala versus intentional engagement of STS in social judgment.

Face repetition effects in implicit and explicit memory tests as measured by fMRI

Recent parallels between neurophysiological and neuroimaging findings suggest that repeated stimulus processing produces decreased responses in brain regions associated with that processing--a 'repetition suppression' effect. In the present study, volunteers performed two tasks on repeated presentation of famous and unfamiliar faces during functional magnetic resonance imaging (fMRI). In the implicit task, they made fame-judgements (regardless of repetition); in the explicit task, they made episodic recognition judgements (regardless of familiarity). Only in the implicit task was repetition suppression observed: for famous faces in a right lateral fusiform region, and for both famous and unfamiliar faces in a left inferior occipital region. Repetition suppression is therefore not an automatic consequence of repeated perceptual processing of stimuli.

Dissociable human perirhinal, hippocampal, and parahippocampal roles during verbal encoding

The precise contribution of perirhinal cortex to human episodic memory is uncertain. Human intracranial recordings highlight a role in successful episodic memory encoding, but encoding-related perirhinal activation has not been observed with functional imaging. By adapting functional magnetic resonance imaging scanning parameters to maximize sensitivity to medial temporal lobe activity, we demonstrate that left perirhinal and hippocampal responses during word list encoding are greater for subsequently recalled than forgotten words. Although perirhinal responses predict memory for all words, successful encoding of initial words in a list, demonstrating a primacy effect, is associated with parahippocampal and anterior hippocampal activation. We conclude that perirhinal cortex and hippocampus participate in successful memory encoding. Encoding-related parahippocampal and anterior hippocampal responses for initial, remembered words most likely reflects enhanced attentional orienting to these positionally distinctive items.

A novel presenilin mutation (M233V) causing very early onset Alzheimer's disease with Lewy bodies

Presenilin 1 mutations are the major cause of autosomal dominant Alzheimer's disease: here we identify a new missense mutation causing a methionine to valine change at codon 233. This codon is homologous to a pathogenic presenilin 2 mutation with the same base change (ATG to GTG) and amino acid change (M239V). This mutation causes disease with an exceptionally early onset age (approximately 30 years) in which pathological examination shows extensive Lewy bodies as well as plaques and tangles.

Anterior prefrontal cortex mediates rule learning in humans

Despite a need for rule learning in everyday life, the brain regions involved in explicit rule induction remain undetermined. Here we use event-related functional magnetic resonance imaging to measure learning-dependent neuronal responses during an explicit categorization task. Subjects made category decisions, with feedback, to exemplar letter strings for which the rule governing category membership was periodically changed. Bilateral fronto-polar prefrontal cortices were selectively engaged following rule change. This activation pattern declined with improving task performance reflecting rule acquisition. The vocabulary of letters comprising the exemplars was also periodically changed, independently of rule changes. This exemplar change modulated activation in left anterior hippocampus. Our finding that fronto-polar cortex mediates rule learning supports a functional contribution of this region to generic reasoning and problem-solving behaviours.

Modulation of auditory neural responses by a visual context in human fear conditioning

Responses to a stimulus signaling danger depend not only on the nature of that stimulus, but also on the context in which it is presented. A large body of work has been conducted in experimental animals investigating the neural correlates of contextual modulation of fear responses. However, much less is known about this process in humans. In this study we used functional MRI in a fear conditioning paradigm to explore this phenomenon. Responses to acoustic conditioned stimuli in auditory cortex were modulated by the presence of a visual context which signaled the likelihood of receiving an aversive unconditioned stimulus. Furthermore, the presence of the aversive visual context was associated with enhanced activity in parietal cortex, which may reflect an increase in attention to the presence of environmental threat stimuli.

Reward value of attractiveness and gaze

Faces are visual objects in our environment that provide strong social cues, with the eyes assuming particular importance. Here we show that the perceived attractiveness of an unfamiliar face increases brain activity in the ventral striatum of the viewer when meeting the person's eye, and decreases activity when eye gaze is directed away. Depending on the direction of gaze, attractiveness can thus activate dopaminergic regions that are strongly linked to reward prediction, indicating that central reward systems may be engaged during the initiation of social interactions.

Neural activity associated with episodic memory for emotional context

To address the question of which brain regions subserve retrieval of emotionally-valenced memories, we used event-related fMRI to index neural activity during the incidental retrieval of emotional and non-emotional contextual information. At study, emotionally neutral words were presented in the context of sentences that were either negatively, neutrally or positively valenced. At test, fMRI data were obtained while participants discriminated between studied and unstudied words. Recognition of words presented in emotionally negative relative to emotionally neutral contexts was associated with enhanced activity in right dorsolateral prefrontal cortex, left amygdala and hippocampus, right lingual gyrus and posterior cingulate cortex. Recognition of words from positive relative to neutral contexts was associated with increased activity in bilateral prefrontal and orbitofrontal cortices, and left anterior temporal lobe. These findings suggest that neural activity mediating episodic retrieval of contextual information and its subsequent processing is modulated by emotion in at least two ways. First, there is enhancement of activity in networks supporting episodic retrieval of neutral information. Second, regions known to be activated when emotional information is encountered in the environment are also active when emotional information is retrieved from memory.

Functional neuroanatomy of three-term relational reasoning

In a recent study we demonstrated that reasoning with categorical syllogisms engages two dissociable mechanisms. Reasoning involving concrete sentences engaged a left hemisphere linguistic system while formally identical arguments, involving abstract sentences, recruited a parietal spatial network. The involvement of a parietal visuo-spatial system in abstract syllogism reasoning raised the question whether argument forms involving explicit spatial relations (or relations that can be easily mapped onto spatial relations) are sufficient to engage the parietal system? We addressed this question in an event-related fMRI study of three-term relational reasoning, using sentences with concrete and abstract content. Our findings indicate that both concrete and abstract three-term relational arguments activate a similar bilateral occipital-parietal-frontal network. However, the abstract reasoning condition engendered greater parietal activation than the concrete reasoning condition. We conclude that arguments involving relations that can be easily mapped onto explicit spatial relations engage a visuo-spatial system, irrespective of concrete or abstract content.

Pharmacological modulation of behavioral and neuronal correlates of repetition priming

In this experiment we address the pharmacological modulation of repetition priming, a basic form of learning, using event-related functional magnetic resonance imaging. We measured brain activity in a word-stem completion paradigm in which, before study, volunteers were given either placebo, lorazepam (2 mg orally), or scopolamine (0.4 mg, i.v.). Relative to placebo, both drugs attenuated the behavioral expression of priming. Repetition was associated with a decreased neuronal response in left extrastriate, left middle frontal, and left inferior frontal cortices in the placebo group. Both drugs abolished these "repetition suppression" effects. By showing a concurrence of behavioral and neuronal modulations, the results suggest that GABAergic and cholinergic systems influence the neuronal plasticity necessary for repetition priming.

Crossmodal binding of fear in voice and face

In social environments, multiple sensory channels are simultaneously engaged in the service of communication. In this experiment, we were concerned with defining the neuronal mechanisms for a perceptual bias in processing simultaneously presented emotional voices and faces. Specifically, we were interested in how bimodal presentation of a fearful voice facilitates recognition of fearful facial expression. By using event-related functional MRI, that crossed sensory modality (visual or auditory) with emotional expression (fearful or happy), we show that perceptual facilitation during face fear processing is expressed through modulation of neuronal responses in the amygdala and the fusiform cortex. These data suggest that the amygdala is important for emotional crossmodal sensory convergence with the associated perceptual bias during fear processing, being mediated by task-related modulation of face-processing regions of fusiform cortex.

Involvement of human amygdala and orbitofrontal cortex in hunger-enhanced memory for food stimuli

We used positron emission tomography to measure regional cerebral blood flow (rCBF) in 10 healthy volunteers performing a recognition memory task with food and non-food items. The biological salience of the food stimuli was manipulated by requiring subjects to fast before the experiment and eat to satiation at fixed time points during scanning. All subjects showed enhanced recognition of food stimuli (relative to non-food) in the fasting state. Satiation significantly reduced the memory advantage for food. Left amygdala rCBF covaried positively with recognition memory for food items, whereas rCBF in right anterior orbitofrontal cortex covaried with overall memory performance. Right posterior orbitofrontal rCBF covaried positively with hunger ratings during presentation of food items. Regression analysis of the neuroimaging data revealed that left amygdala and right lateral orbitofrontal rCBF covaried as a function of stimulus category (i.e., food vs non-food). These results indicate the involvement of amygdala and discrete regions of orbitofrontal cortex in the integration of perceptual (food), motivational (hunger), and cognitive (memory) processes in the human brain.

Differential extrageniculostriate and amygdala responses to presentation of emotional faces in a cortically blind field

Patient G.Y. is able to discriminate emotional facial expressions presented in his blind (right) hemifield despite an extensive lesion of the corresponding (left) striate cortex. One proposal is that this residual ability (affective "blindsight") depends on a subcortical visual pathway comprising the superior colliculus, posterior (extrageniculate) thalamus and amygdala. Here we report differential amygdala responses in G.Y. to presentation of fearful and fear-conditioned faces in his blind (right) hemifield. These amygdala responses exhibited condition-dependent covariation with neural activity in the posterior thalamus and superior colliculus. Our results provide further evidence that an extrageniculostriate (colliculo-thalamo-amygdala) neural pathway can process fear-related stimuli independently of both the striate cortex and normal phenomenal visual awareness.

Seen Gaze-Direction Modulates Fusiform Activity and Its Coupling with Other Brain Areas during Face Processing

Gaze-contact is often a preliminary to social interaction and so constitutes a signal for the allocation of processing resources to the gazing face. We investigated how gaze direction influences face processing in an fMRI study, where seen gaze and head direction could independently be direct or deviated. Direct relative to averted gaze elicited stronger activation for faces in ventral occipitotemporal cortices around the fusiform gyrus, regardless of head orientation. Moreover, direct gaze led to greater correlation between activity in the fusiform and the amygdala, a region associated with emotional responses and stimulus saliency. By contrast, faces with averted gaze (again, regardless of head orientation) yielded increased correlation between activity in the fusiform and the intraparietal sulcus, a region associated with shifting attention to the periphery.

Effects of attention and emotion on face processing in the human brain: an event-related fMRI study

We used event-related fMRI to assess whether brain responses to fearful versus neutral faces are modulated by spatial attention. Subjects performed a demanding matching task for pairs of stimuli at prespecified locations, in the presence of task-irrelevant stimuli at other locations. Faces or houses unpredictably appeared at the relevant or irrelevant locations, while the faces had either fearful or neutral expressions. Activation of fusiform gyri by faces was strongly affected by attentional condition, but the left amygdala response to fearful faces was not. Right fusiform activity was greater for fearful than neutral faces, independently of the attention effect on this region. These results reveal differential influences on face processing from attention and emotion, with the amygdala response to threat-related expressions unaffected by a manipulation of attention that strongly modulates the fusiform response to faces.