Neural correlates of visual working memory: fMRI amplitude predicts task performance

We used fMRI to investigate how moment-to-moment neural activity contributes to success or failure on individual trials of a visual working memory (WM) task. We found that different nodes of a distributed cortical network were activated to a greater extent for correct compared to incorrect trials during stimulus encoding, memory maintenance during delays, and at test. A logistic regression analysis revealed that the fMRI signal amplitude during the delay interval in a network of frontoparietal regions predicted successful performance on a trial-by-trial basis. Differential delay activity occurred even for only those trials in which BOLD activity during encoding was strong, demonstrating that it was not a simple consequence of effective versus ineffective encoding. Our results indicate that accurate memory depends on strong sustained signals that span the delay interval of WM tasks.     

Neural substrates of spontaneous musical performance: an FMRI study of jazz improvisation

To investigate the neural substrates that underlie spontaneous musical performance, we examined improvisation in professional jazz pianists using functional MRI. By employing two paradigms that differed widely in musical complexity, we found that improvisation (compared to production of over-learned musical sequences) was consistently characterized by a dissociated pattern of activity in the prefrontal cortex: extensive deactivation of dorsolateral prefrontal and lateral orbital regions with focal activation of the medial prefrontal (frontal polar) cortex. Such a pattern may reflect a combination of psychological processes required for spontaneous improvisation, in which internally motivated, stimulus-independent behaviors unfold in the absence of central processes that typically mediate self-monitoring and conscious volitional control of ongoing performance. Changes in prefrontal activity during improvisation were accompanied by widespread activation of neocortical sensorimotor areas (that mediate the organization and execution of musical performance) as well as deactivation of limbic structures (that regulate motivation and emotional tone). This distributed neural pattern may provide a cognitive context that enables the emergence of spontaneous creative activity.     

Neural correlates of perceiving emotional faces and bodies in developmental prosopagnosia: an event-related fMRI-study

Many people experience transient difficulties in recognizing faces but only a small number of them cannot recognize their family members when meeting them unexpectedly. Such face blindness is associated with serious problems in everyday life. A better understanding of the neuro-functional basis of impaired face recognition may be achieved by a careful comparison with an equally unique object category and by a adding a more realistic setting involving neutral faces as well facial expressions. We used event-related functional magnetic resonance imaging (fMRI) to investigate the neuro-functional basis of perceiving faces and bodies in three developmental prosopagnosics (DP) and matched healthy controls. Our approach involved materials consisting of neutral faces and bodies as well as faces and bodies expressing fear or happiness. The first main result is that the presence of emotional information has a different effect in the patient vs. the control group in the fusiform face area (FFA). Neutral faces trigger lower activation in the DP group, compared to the control group, while activation for facial expressions is the same in both groups. The second main result is that compared to controls, DPs have increased activation for bodies in the inferior occipital gyrus (IOG) and for neutral faces in the extrastriate body area (EBA), indicating that body and face sensitive processes are less categorically segregated in DP. Taken together our study shows the importance of using naturalistic emotional stimuli for a better understanding of developmental face deficits.     

No enhanced recognition memory,but better source memory for faces of cheaters

Previous studies sought to test for the existence of a “cheater-detection module” by testing for enhanced memory for the faces of cheaters, but past results have been inconclusive. Here, we present four experiments showing that old–new discrimination was not affected by whether a face was associated with a history of cheating, trustworthy or irrelevant behavior. In contrast, source memory for faces associated with a history of cheating (i.e., memory for the cheating context in which the face was encountered) was consistently better than source memory for other types of faces. This pattern held under a variety of conditions, including different types of judgments participants made about the stimulus persons (attractiveness in Experiment 1; likeability in Experiments 2–4), different retention intervals (a few minutes in Experiments 1, 2 and 4; 1 week in Experiment 3), whether the behaviors were exceptional or ordinary (Experiments 1–3) and whether the social status of the characters was low or high (Experiment 4). Given no differences in old–new discrimination, enhanced source memory for faces of cheaters may be useful for avoiding cheaters in future interactions.     

The effect of negative and positive emotionality on associative memory: an FMRI study

In general, emotion is known to enhance memory processes. However, the effect of emotion on associative memory and the underling neural mechanisms remains largely unexplored. In this study, we explored brain activation during an associative memory task that involved the encoding and retrieval of word and face pairs. The word and face pairs consisted of either negative or positive words with neutral faces. Significant hippocampal activation was observed during both encoding and retrieval, regardless of whether the word was negative or positive. Negative and positive emotionality differentially affected the hemodynamic responses to encoding and retrieval in the amygdala, with increased responses during encoding negative word and face pairs. Furthermore, activation of the amygdala during encoding of negative word and neutral face pairs was inversely correlated with subsequent memory retrieval. These findings suggest that activation of the amygdala induced by negative emotion during encoding may disrupt associative memory performance.     

Neural correlates of the difference between working memory speed and simple sensorimotor speed: an fMRI study

The difference between the speed of simple cognitive processes and the speed of complex cognitive processes has various psychological correlates. However, the neural correlates of this difference have not yet been investigated. In this study, we focused on working memory (WM) for typical complex cognitive processes. Functional magnetic resonance imaging data were acquired during the performance of an N-back task, which is a measure of WM for typical complex cognitive processes. In our N-back task, task speed and memory load were varied to identify the neural correlates responsible for the difference between the speed of simple cognitive processes (estimated from the 0-back task) and the speed of WM. Our findings showed that this difference was characterized by the increased activation in the right dorsolateral prefrontal cortex (DLPFC) and the increased functional interaction between the right DLPFC and right superior parietal lobe. Furthermore, the local gray matter volume of the right DLPFC was correlated with participants' accuracy during fast WM tasks, which in turn correlated with a psychometric measure of participants' intelligence. Our findings indicate that the right DLPFC and its related network are responsible for the execution of the fast cognitive processes involved in WM. Identified neural bases may underlie the psychometric differences between the speed with which subjects perform simple cognitive tasks and the speed with which subjects perform more complex cognitive tasks, and explain the previous traditional psychological findings.     

Neural correlates of visual motion prediction

Predicting the trajectories of moving objects in our surroundings is important for many life scenarios, such as driving, walking, reaching, hunting and combat. We determined human subjects' performance and task-related brain activity in a motion trajectory prediction task. The task required spatial and motion working memory as well as the ability to extrapolate motion information in time to predict future object locations. We showed that the neural circuits associated with motion prediction included frontal, parietal and insular cortex, as well as the thalamus and the visual cortex. Interestingly, deactivation of many of these regions seemed to be more closely related to task performance. The differential activity during motion prediction vs. direct observation was also correlated with task performance. The neural networks involved in our visual motion prediction task are significantly different from those that underlie visual motion memory and imagery. Our results set the stage for the examination of the effects of deficiencies in these networks, such as those caused by aging and mental disorders, on visual motion prediction and its consequences on mobility related daily activities.     

Neural basis of self and other representation in autism: an FMRI study of self-face recognition

Background

Autism is a developmental disorder characterized by decreased interest and engagement in social interactions and by enhanced self-focus. While previous theoretical approaches to understanding autism have emphasized social impairments and altered interpersonal interactions, there is a recent shift towards understanding the nature of the representation of the self in individuals with autism spectrum disorders (ASD). Still, the neural mechanisms subserving self-representations in ASD are relatively unexplored.

Methodology/Principal Findings

We used event-related fMRI to investigate brain responsiveness to images of the subjects'' own face and to faces of others. Children with ASD and typically developing (TD) children viewed randomly presented digital morphs between their own face and a gender-matched other face, and made “self/other” judgments. Both groups of children activated a right premotor/prefrontal system when identifying images containing a greater percentage of the self face. However, while TD children showed activation of this system during both self- and other-processing, children with ASD only recruited this system while viewing images containing mostly their own face.

Conclusions/Significance

This functional dissociation between the representation of self versus others points to a potential neural substrate for the characteristic self-focus and decreased social understanding exhibited by these individuals, and suggests that individuals with ASD lack the shared neural representations for self and others that TD children and adults possess and may use to understand others.     

Origins of spatial working memory deficits in schizophrenia: an event-related FMRI and near-infrared spectroscopy study

Abnormal prefrontal functioning plays a central role in the working memory (WM) deficits of schizophrenic patients, but the nature of the relationship between WM and prefrontal activation remains undetermined. Using two functional neuroimaging methods, we investigated the neural correlates of remembering and forgetting in schizophrenic and healthy participants. We focused on the brain activation during WM maintenance phase with event-related functional magnetic resonance imaging (fMRI). We also examined oxygenated hemoglobin changes in relation to memory performance with the near-infrared spectroscopy (NIRS) using the same spatial WM task. Distinct types of correct and error trials were segregated for analysis. fMRI data indicated that prefrontal activation was increased during WM maintenance on correct trials in both schizophrenic and healthy subjects. However, a significant difference was observed in the functional asymmetry of frontal activation pattern. Healthy subjects showed increased activation in the right frontal, temporal and cingulate regions. Schizophrenic patients showed greater activation compared with control subjects in left frontal, temporal and parietal regions as well as in right frontal regions. We also observed increased 'false memory' errors in schizophrenic patients, associated with increased prefrontal activation and resembling the activation pattern observed on the correct trials. NIRS data replicated the fMRI results. Thus, increased frontal activity was correlated with the accuracy of WM in both healthy control and schizophrenic participants. The major difference between the two groups concerned functional asymmetry; healthy subjects recruited right frontal regions during spatial WM maintenance whereas schizophrenic subjects recruited a wider network in both hemispheres to achieve the same level of memory performance. Increased "false memory" errors and accompanying bilateral prefrontal activation in schizophrenia suggest that the etiology of memory errors must be considered when comparing group performances. Finally, the concordance of fMRI and NIRS data supports NIRS as an alternative functional neuroimaging method for psychiatric research.     

Neural correlates for feeling-of-knowing: an fMRI parametric analysis

The "feeling-of-knowing" (FOK) is a subjective sense of knowing a word before recalling it, and the FOK provides us clues to understanding the mechanisms of human metamemory systems. We investigated neural correlates for the FOK based on the recall-judgment-recognition paradigm. Event-related functional magnetic resonance imaging with a parametric analysis was used. We found activations in left dorsolateral, left anterior, bilateral inferior, and medial prefrontal cortices that significantly increased as the FOK became greater, and the activations remained significant even when the potentially confounding factor of the response latency was removed. Furthermore, we demonstrated that the FOK region in the right inferior frontal gyrus and a subset of the FOK region in the left inferior frontal gyrus are not recruited for successful recall processes, suggesting their particular role in metamemory processing.     

Neural correlates of visual localization and perisaccadic mislocalization

While reading this text, your eyes jump from word to word. Yet you are unaware of the motion this causes on your retina; the brain somehow compensates for these displacements and creates a stable percept of the world. This compensation is not perfect; perisaccadically, perceptual space is distorted. We show that this distortion can be traced to a representation of retinal position in the medial temporal and medial superior temporal areas. These cells accurately represent retinal position during fixation, but perisaccadically, the same cells distort the representation of space. The time course and magnitude of this distortion are similar to the mislocalization found psychophysically in humans. This challenges the assumption in many psychophysical studies that the perisaccadic retinal position signal is veridical.     

Reward-related FMRI activation of dopaminergic midbrain is associated with enhanced hippocampus-dependent long-term memory formation

Long-term potentiation in the hippocampus can be enhanced and prolonged by dopaminergic inputs from midbrain structures such as the substantia nigra. This improved synaptic plasticity is hypothesized to be associated with better memory consolidation in the hippocampus. We used a condition that reliably elicits a dopaminergic response, reward anticipation, to study the relationship between activity of dopaminergic midbrain areas and hippocampal long-term memory in healthy adults. Pictures of object drawings that predicted monetary reward were associated with stronger fMRI activity in reward-related brain areas, including the substantia nigra, compared with non-reward-predicting pictures. Three weeks later, recollection and source memory were better for reward-predicting than for non-reward-predicting pictures. FMRI activity in the hippocampus and the midbrain was higher for reward-predicting pictures that were later recognized compared with later forgotten pictures. These data are consistent with the hypothesis that activation of dopaminergic midbrain regions enhances hippocampus-dependent memory formation, possibly by enhancing consolidation.     

Context effects on the neural correlates of recognition memory: an electrophysiological study

Event-related potentials (ERPs) were recorded during a recognition memory test for previously studied visual objects. Some studied objects were paired with the same context (landscape scenes) as at study, some were superimposed on a different studied context, and some were paired with new contexts. Unstudied objects were paired with either a studied or a new context. Three ERP memory effects were observed: an early effect elicited by all stimuli containing at least one studied component; a second effect elicited only by stimuli in which both object and context had been studied; and a third effect elicited by stimuli containing a studied object. Thus, test stimuli engaged three distinct kinds of memory-related neural activity which differed in their specificity for task-relevant features.     

Neural correlates of the contents of visual awareness in humans

The immediacy and directness of our subjective visual experience belies the complexity of the neural mechanisms involved, which remain incompletely understood. This review focuses on how the subjective contents of human visual awareness are encoded in neural activity. Empirical evidence to date suggests that no single brain area is both necessary and sufficient for consciousness. Instead, necessary and sufficient conditions appear to involve both activation of a distributed representation of the visual scene in primary visual cortex and ventral visual areas, plus parietal and frontal activity. The key empirical focus is now on characterizing qualitative differences in the type of neural activity in these areas underlying conscious and unconscious processing. To this end, recent progress in developing novel approaches to accurately decoding the contents of consciousness from brief samples of neural activity show great promise.     

The neural basis of hyperlexic reading: an FMRI case study

Children with autism spectrum disorders in very rare cases display surprisingly advanced "hyperlexic" reading skills. Using functional magnetic resonance imaging (fMRI), we studied the neural basis of this precocious reading ability in a 9-year-old hyperlexic boy who reads 6 years in advance of his age. During covert reading, he demonstrated greater activity in the left inferior frontal and superior temporal cortices than both chronological age- and reading age-matched controls. Activity in the right inferior temporal sulcus was greater when compared to reading age-matched controls. These findings suggest that precocious reading is brought about by simultaneously drawing on both left hemisphere phonological and right hemisphere visual systems, reconciling the two prevailing, but seemingly contradictory, single hemisphere theories of hyperlexia. Hyperlexic reading is therefore associated with hyperactivation of the left superior temporal cortex, much in the same way as developmental dyslexia is associated with hypoactivation of this area.     

Mechanism of case processing in the brain: an FMRI study

In sentence comprehension research, the case system, which is one of the subsystems of the language processing system, has been assumed to play a crucial role in signifying relationships in sentences between noun phrases (NPs) and other elements, such as verbs, prepositions, nouns, and tense. However, so far, less attention has been paid to the question of how cases are processed in our brain. To this end, the current study used fMRI and scanned the brain activity of 15 native English speakers during an English-case processing task. The results showed that, while the processing of all cases activates the left inferior frontal gyrus and posterior part of the middle temporal gyrus, genitive case processing activates these two regions more than nominative and accusative case processing. Since the effect of the difference in behavioral performance among these three cases is excluded from brain activation data, the observed different brain activations would be due to the different processing patterns among the cases, indicating that cases are processed differently in our brains. The different brain activations between genitive case processing and nominative/accusative case processing may be due to the difference in structural complexity between them.     

Evidence for thalamic involvement in the thermal grill illusion: an FMRI study

Background

Perceptual illusions play an important role in untangling neural mechanisms underlying conscious phenomena. The thermal grill illusion (TGI) has been suggested as a promising model for exploring percepts involved in neuropathic pain, such as cold-allodynia (pain arising from contact with innocuous cold). The TGI is an unpleasant/painful sensation from touching juxtapositioned bars of cold and warm innocuous temperatures.

Aim

To develop an MRI-compatible TGI-unit and explore the supraspinal correlates of the illusion, using fMRI, in a group of healthy volunteers.

Methods

We constructed a TGI-thermode allowing the rapid presentation of warm(41°C), cold(18°C) and interleaved(41°C+18°C = TGI) temperatures in an fMRI-environment. Twenty volunteers were tested. The affective-motivational (“unpleasantness”) and sensory-disciminatory (“pain-intensity”) dimensions of each respective stimulus were rated. Functional images were analyzed at a corrected α-level <0.05.

Results

The TGI was rated as significantly more unpleasant and painful than stimulation with each of its constituent temperatures. Also, the TGI was rated as significantly more unpleasant than painful. Thermal stimulation versus neutral baseline revealed bilateral activations of the anterior insulae and fronto-parietal regions. Unlike its constituent temperatures the TGI displayed a strong activation of the right (contralateral) thalamus. Exploratory contrasts at a slightly more liberal threshold-level also revealed a TGI-activation of the right mid/anterior insula, correlating with ratings of unpleasantness(rho = 0.31).

Conclusion/Significance

To the best of our knowledge, this is the first fMRI-study of the TGI. The activation of the anterior insula is consistent with this region''s putative role in processing of homeostatically relevant feeling-states. Our results constitute the first neurophysiologic evidence of thalamic involvement in the TGI. Similar thalamic activity has previously been observed during evoked cold-allodynia in patients with central neuropathic pain. Our results further the understanding of the supraspinal correlates of the TGI-phenomenon and pave the way for future inquiries into if and how it may relate to neuropathic pain.     

Transcription: a mechanism for short-term memory

Yeast growing for a considerable time in glucose 'remember' a previous exposure to galactose, the inducer of its galactose-utilization (GAL) genes. This memory is conveyed by a cytoplasmically transmitted galactokinase working as a signal transducer.     

Dissociated representations of pleasant and unpleasant olfacto-trigeminal mixtures: an FMRI study

How the pleasantness of chemosensory stimuli such as odorants or intranasal trigeminal compounds is processed in the human brain has been the focus of considerable recent interest. Yet, so far, only the unimodal form of this hedonic processing has been explored, and not its bimodal form during crossmodal integration of olfactory and trigeminal stimuli. The main purpose of the present study was to investigate this question. To this end, functional magnetic resonance imaging (fMRI) was used in an experiment comparing brain activation related to a pleasant and a relatively unpleasant olfacto-trigeminal mixture, and to their individual components (CO(2) alone, Orange alone, Rose alone). Results revealed first common neural activity patterns in response to both mixtures in a number of regions: notably the superior temporal gyrus and the caudate nucleus. Common activations were also observed in the insula, although the pleasant mixture activated the right insula whereas the unpleasant mixture activated the left insula. However, specific activations were observed in anterior cingulate gyrus and the ventral tegmental area only during the perception of the pleasant mixture. These findings emphasized for the firs time the involvement of the latter structures in processing of pleasantness during crossmodal integration of chemosensory stimuli.