Detecting latency differences in event-related BOLD responses: application to words versus nonwords and initial versus repeated face presentations

Complex-number representation of informed basis functions in general linear modeling of Functional Magnetic Resonance Imaging

Functional Magnetic Resonance Imaging (fMRI), measuring Blood Oxygen Level-Dependent (BOLD), is a widely used tool to reveal spatiotemporal pattern of neural activity in human brain. Standard analysis of fMRI data relies on a general linear model and the model is constructed by convolving the task stimuli with a hypothesized hemodynamic response function (HRF). To capture possible phase shifts in the observed BOLD response, the informed basis functions including canonical HRF and its temporal derivative, have been proposed to extend the hypothesized hemodynamic response in order to obtain a good fitting model. Different t contrasts are constructed from the estimated model parameters for detecting the neural activity between different task conditions. However, the estimated model parameters corresponding to the orthogonal basis functions have different physical meanings. It remains unclear how to combine the neural features detected by the two basis functions and construct t contrasts for further analyses. In this paper, we have proposed a novel method for representing multiple basis functions in complex domain to model the task-driven fMRI data. Using this method, we can treat each pair of model parameters, corresponding respectively to canonical HRF and its temporal derivative, as one complex number for each task condition. Using the specific rule we have defined, we can conveniently perform arithmetical operations on the estimated model parameters and generate different t contrasts. We validate this method using the fMRI data acquired from twenty-two healthy participants who underwent an auditory stimulation task.

Whole-brain, time-locked activation with simple tasks revealed using massive averaging and model-free analysis

The brain is the body's largest energy consumer, even in the absence of demanding tasks. Electrophysiologists report on-going neuronal firing during stimulation or task in regions beyond those of primary relationship to the perturbation. Although the biological origin of consciousness remains elusive, it is argued that it emerges from complex, continuous whole-brain neuronal collaboration. Despite converging evidence suggesting the whole brain is continuously working and adapting to anticipate and actuate in response to the environment, over the last 20 y, task-based functional MRI (fMRI) have emphasized a localizationist view of brain function, with fMRI showing only a handful of activated regions in response to task/stimulation. Here, we challenge that view with evidence that under optimal noise conditions, fMRI activations extend well beyond areas of primary relationship to the task; and blood-oxygen level-dependent signal changes correlated with task-timing appear in over 95% of the brain for a simple visual stimulation plus attention control task. Moreover, we show that response shape varies substantially across regions, and that whole-brain parcellations based on those differences produce distributed clusters that are anatomically and functionally meaningful, symmetrical across hemispheres, and reproducible across subjects. These findings highlight the exquisite detail lying in fMRI signals beyond what is normally examined, and emphasize both the pervasiveness of false negatives, and how the sparseness of fMRI maps is not a result of localized brain function, but a consequence of high noise and overly strict predictive response models.

Repetition Priming and Repetition Suppression: A Case for Enhanced Efficiency Through Neural Synchronization

Stimulus repetition in identification tasks leads to improved behavioral performance ("repetition priming") but attenuated neural responses ("repetition suppression") throughout task-engaged cortical regions. While it's clear that this pervasive brain-behavior relationship reflects some form of improved processing efficiency, the exact form that it takes remains elusive. In this Discussion Paper, we review four different theoretical proposals that have the potential to link repetition suppression and priming, with a particular focus on a proposal that stimulus repetition affects improved efficiency through enhanced neural synchronization. We argue that despite exciting recent work on the role of neural synchronization in cognitive processes such as attention and perception, similar studies in the domain of learning and memory - and priming, in particular - have been lacking. We emphasize the need for new studies with adequate spatiotemporal resolution, formulate several novel predictions, and discuss our ongoing efforts to disentangle the current proposals.

Premotor Cortex Is Sensitive to Auditory–Visual Congruence for Biological Motion

The auditory and visual perception systems have developed special processing strategies for ecologically valid motion stimuli, utilizing some of the statistical properties of the real world. A well-known example is the perception of biological motion, for example, the perception of a human walker. The aim of the current study was to identify the cortical network involved in the integration of auditory and visual biological motion signals. We first determined the cortical regions of auditory and visual coactivation (Experiment 1); a conjunction analysis based on unimodal brain activations identified four regions: middle temporal area, inferior parietal lobule, ventral premotor cortex, and cerebellum. The brain activations arising from bimodal motion stimuli (Experiment 2) were then analyzed within these regions of coactivation. Auditory footsteps were presented concurrently with either an intact visual point-light walker (biological motion) or a scrambled point-light walker; auditory and visual motion in depth (walking direction) could either be congruent or incongruent. Our main finding is that motion incongruency (across modalities) increases the activity in the ventral premotor cortex, but only if the visual point-light walker is intact. Our results extend our current knowledge by providing new evidence consistent with the idea that the premotor area assimilates information across the auditory and visual modalities by comparing the incoming sensory input with an internal representation.

Exploring perceptual processing of ASL and human actions: effects of inversion and repetition priming

In this paper, we compare responses of deaf signers and hearing non-signers engaged in a categorization task of signs and non-linguistic human actions. We examine the time it takes to make such categorizations under conditions of 180° stimulus inversion and as a function of repetition priming, in an effort to understand whether the processing of sign language forms draws upon special processing mechanisms or makes use of mechanisms used in recognition of non-linguistic human actions. Our data show that deaf signers were much faster in the categorization of both linguistic and non-linguistic actions, and relative to hearing non-signers, show evidence that they were more sensitive to the configural properties of signs. Our study suggests that sign expertise may lead to modifications of a general-purpose human action recognition system rather than evoking a qualitatively different mode of processing, and supports the contention that signed languages make use of perceptual systems through which humans understand or parse human actions and gestures more generally.

The continuing challenge of understanding and modeling hemodynamic variation in fMRI

Interpretation of fMRI data depends on our ability to understand or model the shape of the hemodynamic response (HR) to a neural event. Although the HR has been studied almost since the beginning of fMRI, we are still far from having robust methods to account for the full range of known HR variation in typical fMRI analyses. This paper reviews how the authors and others contributed to our understanding of HR variation. We present an overview of studies that describe HR variation across voxels, healthy volunteers, populations, and dietary or pharmaceutical modulations. We also describe efforts to minimize the effects of HR variation in intrasubject, group, population, and connectivity analyses and the limits of these methods.

An fMRI Study of the Interactions Between the Attention and the Gustatory Networks

In a prior study, we showed that trying to detect a taste in a tasteless solution results in enhanced activity in the gustatory and attention networks. The aim of the current study was to use connectivity analyses to test if and how these networks interact during directed attention to taste. We predicted that the attention network modulates taste cortex, reflecting top-down enhancement of incoming sensory signals that are relevant to goal-directed behavior. fMRI was used to measure brain responses in 14 subjects as they performed two different tasks: (1) trying to detect a taste in a solution or (2) passively perceiving the same solution. We used psychophysiological interaction analysis to identify regions demonstrating increased connectivity during a taste attention task compared to passive tasting. We observed greater connectivity between the anterior cingulate cortex and the frontal eye fields, posterior parietal cortex, and parietal operculum and between the anterior cingulate cortex and the right anterior insula and frontal operculum. These results suggested that selective attention to taste is mediated by a hierarchical circuit in which signals are first sent from the frontal eye fields, posterior parietal cortex, and parietal operculum to the anterior cingulate cortex, which in turn modulates responses in the anterior insula and frontal operculum. We then tested this prediction using dynamic causal modeling. This analysis confirmed a model of indirect modulation of the gustatory cortex, with the strongest influence coming from the frontal eye fields via the anterior cingulate cortex. In summary, the results indicate that the attention network modulates the gustatory cortex during attention to taste and that the anterior cingulate cortex acts as an intermediary processing hub between the attention network and the gustatory cortex.

Functionally specific changes in resting-state sensorimotor networks after motor learning

Motor learning changes the activity of cortical motor and subcortical areas of the brain, but does learning affect sensory systems as well? We examined in humans the effects of motor learning using fMRI measures of functional connectivity under resting conditions and found persistent changes in networks involving both motor and somatosensory areas of the brain. We developed a technique that allows us to distinguish changes in functional connectivity that can be attributed to motor learning from those that are related to perceptual changes that occur in conjunction with learning. Using this technique, we identified a new network in motor learning involving second somatosensory cortex, ventral premotor cortex, and supplementary motor cortex whose activation is specifically related to perceptual changes that occur in conjunction with motor learning. We also found changes in a network comprising cerebellar cortex, primary motor cortex, and dorsal premotor cortex that were linked to the motor aspects of learning. In each network, we observed highly reliable linear relationships between neuroplastic changes and behavioral measures of either motor learning or perceptual function. Motor learning thus results in functionally specific changes to distinct resting-state networks in the brain.

Repetition priming and repetition suppression: Multiple mechanisms in need of testing

In our Discussion Paper, we reviewed four theoretical proposals that have the potential to link the neural and behavioral phenomena of Repetition Suppression and Repetition Priming. We argued that among these proposals, the Synchrony and Bayesian Explaining Away models appear to be the most promising in addressing existing data, and we articulated a series of predictions to distinguish between them. The commentaries have helped to clarify some of these predictions, have highlighted additional evidence supporting the Facilitation and Sharpening models, and have emphasized dissociations by repetition lag and brain location. Our reply addresses these issues in turn, and we argue that progress will require the testing of Repetition Suppression, changes in neural tuning, and changes in synchronization throughout the brain and over a variety of lags and task contexts.

Spatiotemporal properties of cortical haemodynamic response to auditory stimuli in sleeping infants revealed by multi-channel near-infrared spectroscopy

Multi-channel near-infrared spectroscopy (NIRS) has been used as a neuroimaging tool to study functional activation of the developing brain in infants. In this paper, we focus on spatiotemporal dynamics of cortical oxygenation changes during sensory processing in young infants. We use a 94-channel NIRS system to assess the activity of wide regions of the cortex in quietly sleeping three-month-old infants. Auditory stimuli composed of a random sequence of pure tones induced haemodynamic changes not only in the temporal auditory regions, but also in the occipital and frontal regions. Analyses of phase synchronization showed that mutual synchronizations of signal changes among the cortical regions were much stronger than the stimulus-induced synchronizations of signal changes. Furthermore, analyses of phase differences among cortical regions revealed phase advancement of the bilateral temporal auditory regions, and phase gradient in a posterior direction from the temporal auditory regions to the occipital regions and in an anterior direction within the frontal regions. We argue that multi-channel NIRS is capable of detecting the precise timing of cortical activation and its flow in the global network of the developing brain.

The anterior cingulate cortex: monitoring the outcomes of others' decisions

The ability to attribute mental states to others and understand the basis of their decisions is essential for human social interaction. A controversial theory states that this is achieved by simulating another's information processing in one's own neural circuits. The anterior cingulate cortex (ACC) is known to play an important role in the registration of discrepancies between the predicted and actual outcomes of decisions (prediction errors).When positive and negative feedback fails altogether, the failure may also signal errors in the prediction that the outcome of that decision would be informative and guide future decisions. Does the ACC signal that an outcome is unexpectedly uninformative? When an outcome directed to others is uninformative, do we understand their mental states by simulating them in the circuits of the ACC in our own brain? The aim of our study was to test for these two possibilities in the human brain with event-related fMRI. We tested whether the ACC processes errors in the prediction of informative feedback and whether the ACC is also activated when scanned subjects process the same outcomes of another's decisions. We show that each is processed by a separate subregion of the ACC.

Effect of auditory input on activations in infant diverse cortical regions during audiovisual processing

A fundamental question with regard to perceptual development is how multisensory information is processed in the brain during the early stages of development. Although a growing body of evidence has shown the early emergence of modality-specific functional differentiation of the cortical regions, the interplay between sensory inputs from different modalities in the developing brain is not well understood. To study the effects of auditory input during audio-visual processing in 3-month-old infants, we evaluated the spatiotemporal cortical hemodynamic responses of 50 infants while they perceived visual objects with or without accompanying sounds. The responses were measured using 94-channel near-infrared spectroscopy over the occipital, temporal, and frontal cortices. The effects of sound manipulation were pervasive throughout the diverse cortical regions and were specific to each cortical region. Visual stimuli co-occurring with sound induced the early-onset activation of the early auditory region, followed by activation of the other regions. Removal of the sound stimulus resulted in focal deactivation in the auditory regions and reduced activation in the early visual region, the association region of the temporal and parietal cortices, and the anterior prefrontal regions, suggesting multisensory interplay. In contrast, equivalent activations were observed in the lateral occipital and lateral prefrontal regions, regardless of sound manipulation. Our findings indicate that auditory input did not generally enhance overall activation in relation to visual perception, but rather induced specific changes in each cortical region. The present study implies that 3-month-old infants may perceive audio-visual multisensory inputs by using the global network of functionally differentiated cortical regions.

Quantifying hemodynamic refractory bold effects in normal subjects at the single-subject level using an inverse logit fitting procedure

PURPOSE

To evaluate whether hemodynamic refractory effects provoked by repeated visual stimulation can be detected and quantified at the single-subject level using a recently described hemodynamic response function (HRF) fitting algorithm.

MATERIALS AND METHODS

Hemodynamic refractory effects were induced with an easily applicable functional MRI (fMRI) paradigm. A fitting method with inverse logit (IL) functions was applied to quantify net HRFs at the single-subject level with three interstimulus intervals (ISI; 1, 2, and 6 s). The model yielded amplitude, latencies, and width for each HRF.

RESULTS

HRF fitting was possible in 44 of 51 healthy volunteers, with excellent goodness-of-fit (R(2) = 0.9745 ± 0.0241). Refractory effects were most pronounced for the 1-s ISI (P < 0.001) and had nearly disappeared for the 6-s ISI.

CONCLUSION

Quantifying refractory effects in individuals was possible in 86.3% of normal subjects using the IL fitting algorithm. This setup may be suitable to explore such effects in individual patients.

Reward abnormalities among women with full and subthreshold bulimia nervosa: a functional magnetic resonance imaging study

OBJECTIVE

To test the hypothesis that women with full and subthreshold bulimia nervosa show abnormal neural activation in response to food intake and anticipated food intake relative to healthy control women.

METHOD

Females with and without full/subthreshold bulimia nervosa recruited from the community (N = 26) underwent functional magnetic resonance imaging (fMRI) during receipt and anticipated receipt of chocolate milkshake and a tasteless control solution.

RESULTS

Women with bulimia nervosa showed trends for less activation than healthy controls in the right anterior insula in response to anticipated receipt of chocolate milkshake (vs. tasteless solution) and in the left middle frontal gyrus, right posterior insula, right precentral gyrus, and right mid dorsal insula in response to consumptions of milkshake (vs. tasteless solution).

DISCUSSION

Bulimia nervosa may be related to potential hypofunctioning of the brain reward system, which may lead these individuals to binge eat to compensate for this reward deficit, though the hypo-responsivity might be a result of a history of binge eating highly palatable foods.

An FMRI study of self-regulatory control and conflict resolution in adolescents with bulimia nervosa

OBJECTIVE

The authors examined functional activity in the frontostriatal systems that mediate self-regulatory capacities and conflict resolution in adolescents with bulimia nervosa.

METHOD

Functional magnetic resonance imaging was used to compare blood-oxygen-level-dependent response in 18 female adolescents with bulimia nervosa and 18 healthy female age-matched subjects during performance on a Simon spatial incompatibility task. Bayesian analyses were used to compare the two groups on patterns of brain activation during correct responses to conflict stimuli and to explore the effects of antecedent stimulus context on group differences in self-regulation and conflict resolution.

RESULTS

Adolescents with and without bulimia nervosa performed similarly on the task. During correct responses in conflict trials, frontostriatal circuits-including the right inferolateral and dorsolateral prefrontal cortices and putamen-failed to activate to the same degree in adolescents with bulimia nervosa as in healthy comparison subjects. Instead, deactivation was seen in the left inferior frontal gyrus as well as a neural system encompassing the posterior cingulate cortex and superior frontal gyrus. Group differences in cortical and striatal regions were driven by the differential responses to stimuli preceded by conflict and nonconflict stimuli, respectively.

CONCLUSIONS

When engaging the self-regulatory control processes necessary to resolve conflict, adolescents with bulimia nervosa displayed abnormal patterns of activation in frontostriatal and default-mode systems. Their abnormal processing of the antecedent stimulus context conditioned their brain response to conflict differently from that of healthy comparison subjects, specifically in frontal regions. It is suspected that functional disturbances in frontal portions of frontostriatal systems may release feeding behaviors from regulatory control, thereby perpetuating the conflicting desires to consume fattening foods and avoid weight gain that characterize bulimia nervosa.

The anterior insular cortex represents breaches of taste identity expectation

Despite the importance of breaches of taste identity expectation for survival, its neural correlate is unknown. We used fMRI in 16 women to examine brain response to expected and unexpected receipt of sweet taste and tasteless/odorless solutions. During expected trials (70%), subjects heard "sweet" or "tasteless" and received the liquid indicated by the cue. During unexpected trials (30%), subjects heard sweet but received tasteless or they heard tasteless but received sweet. After delivery, subjects indicated stimulus identity by pressing a button. Reaction time was faster and more accurate after valid cuing, indicating that the cues altered expectancy as intended. Tasting unexpected versus expected stimuli resulted in greater deactivation in fusiform gyri, possibly reflecting greater suppression of visual object regions when orienting to, and identifying, an unexpected taste. Significantly greater activation to unexpected versus expected stimuli occurred in areas related to taste (thalamus, anterior insula), reward [ventral striatum (VS), orbitofrontal cortex], and attention [anterior cingulate cortex, inferior frontal gyrus, intraparietal sulcus (IPS)]. We also observed an interaction between stimulus and expectation in the anterior insula (primary taste cortex). Here response was greater for unexpected versus expected sweet compared with unexpected versus expected tasteless, indicating that this region is preferentially sensitive to breaches of taste expectation. Connectivity analyses confirmed that expectation enhanced network interactions, with IPS and VS influencing insular responses. We conclude that unexpected oral stimulation results in suppression of visual cortex and upregulation of sensory, attention, and reward regions to support orientation, identification, and learning about salient stimuli.

Prediction of reading skill several years later depends on age and brain region: implications for developmental models of reading

We investigated whether brain activity was predictive of future reading skill and, if so, how this brain-behavior correlation informs developmental models of reading. A longitudinal study followed 26 normally developing human children ranging in age from 9 to 15 years who were initially assessed for reading skill and performed a rhyming judgment task during functional magnetic resonance imaging. Patterns of brain activation in this task predicted changes between initial and a follow-up assessment of nonword reading skill administered up to 6 years later. Brain activity in areas typically active during imaging studies of reading was found to predict future nonword reading ability, but the predictive ability of these areas depended on age. Increased activity relative to peers in neural circuits associated with phonological recoding (i.e., inferior frontal gyrus and basal ganglia) was predictive of greater gains in reading fluency in younger children, whereas increased activity relative to peers in orthographic processing circuits (i.e., fusiform gyrus) was predictive of smaller gains in fluency for older children. Interpreted within the context of a connectionist model of reading, these results suggest that younger children who are more sensitive to higher-order phonological word characteristics (e.g., coarticulations) may make greater reading proficiency gains, whereas older children who focus more on whole-word orthographic representations may make smaller proficiency gains.

Absence of haemodynamic refractory effects in patients with migraine without aura – an interictal fMRI study

Background: In healthy controls, haemodynamic refractory effects are observed with blood-oxygenation-level dependent (BOLD) functional MRI (fMRI): the haemodynamic response function (HRF) to the second stimulus in a pair of stimuli with short interstimulus interval (ISI) shows a decreased amplitude and an increased time-to-peak. We hypothesize that there may be interictal haemodynamic abnormalities in migraineurs.

Methods: An event-related fMRI design with paired face stimuli and varying ISIs was used to measure interictal HRFs in the face recognition area of patients with migraine without aura (MwoA) and controls. Net responses to the second stimulus in a pair were calculated and averaged per participant. Several characterizing parameters of the net responses were quantified and examined within each group.

Results: Refractory effects were not observed in our patient group. There are no changes in the net responses compared with the reference situation in patients, irrespective of the ISI, whereas in controls all HRF parameters are decreased or delayed for an ISI of 1 second.

Conclusion: This is the first fMRI study investigating the haemodynamic refractory effects in MwoA patients. Unlike in controls, these effects are not observed in migraineurs. Although currently unclear, it is tempting to speculate that this observation reflects the neurovascular correlate of lack of habituation measured with evoked potentials in migraineurs.

Differential magnitude coding of gains and omitted rewards in the ventral striatum

Physiologic studies revealed that neurons in the dopaminergic midbrain of non-human primates encode reward prediction errors. It was furthermore shown that reward prediction errors are adaptively scaled with respect to the range of possible outcomes, enabling sensitive encoding for a large range of reward values. Congruently, neuroimaging studies in humans demonstrated that BOLD-responses in the ventral striatum encode reward prediction errors in similar fashion as dopaminergic midbrain neurons, suggesting that these BOLD-responses may be driven by dopaminergic midbrain activity. However, neuroimaging results are ambiguous with respect to the adaptive scaling of reward prediction errors, leading to the conjecture that under certain circumstances other than dopaminergic midbrain input may drive ventral striatal BOLD-responses. The goal of this study was to substantiate whether BOLD-responses in the ventral striatum rather respond to adaptively scaled reward prediction errors or absolute reward magnitude. In addition, we aimed to identify neuronal structures modulating activity in the ventral striatum. Sixteen healthy participants played a wheel of fortune game, where they could win three differently valued rewards while being scanned. BOLD-responses increased after gaining rewards; this gain was however independent of the absolute reward magnitude. In contrast BOLD-responses upon reward omission decreased with reward magnitude. A psychophysiological interaction analysis identified a cluster in the brainstem in proximity of the dorsal raphe nucleus, a cluster in the lateral orbitofrontal cortex, and a cluster in the rostral cingulate zone. These clusters changed their connectivity with the ventral striatum in relation to the absolute reward magnitude in reward omission trials.

Slice-timing effects and their correction in functional MRI

Exact timing is essential for functional MRI data analysis. Datasets are commonly measured using repeated 2D imaging methods, resulting in a temporal offset between slices. To compensate for this timing difference, slice-timing correction (i.e. temporal data interpolation) has been used as an fMRI pre-processing step for more than fifteen years. However, there has been an ongoing debate about the effectiveness and applicability of this method. This paper presents the first elaborated analysis of the impact of the slice-timing effect on simulated data for different fMRI paradigms and measurement parameters, taking into account data noise and smoothing effects. Here we show, depending on repetition time and paradigm design, slice-timing effects can significantly impair fMRI results and slice-timing correction methods can successfully compensate for these effects and therefore increase the robustness of the data analysis. In addition, our results from simulated data were supported by empirical in vivo datasets. Our findings suggest that slice-timing correction should be included in the fMRI pre-processing pipeline.

Modality-specific neural effects of selective attention to taste and odor

The insular cortex is implicated in general attention and in taste perception. The effect of selective attention to taste on insular responses may therefore reflect a general effect of attention or it may be (taste) modality specific. To distinguish between these 2 possibilities, we used functional magnetic resonance imaging to evaluate brain response to tastes and odors while subjects passively sampled the stimuli or performed a detection task. We found that trying to detect a taste (attention to taste) resulted in activation of the primary taste cortex (anterior and mid-dorsal insula) but not in the primary olfactory cortex (piriform). In contrast, trying to detect an odor (attention to odor) increased activity in primary olfactory but not primary gustatory cortex. However, we did identify a region of far anterior insular cortex that responded to both taste and odor "searches." These results demonstrate modality-specific activation of primary taste cortex by attention to taste and primary olfactory cortex by attention to odor and rule out the possibility that either response reflects a general effect of attentional deployment. The findings also support the existence of a multimodal region in far anterior insular cortex that is sensitive to directed attention to taste and smell.

Estimating neural signal dynamics in the human brain

Although brain imaging methods are highly effective for localizing the effects of neural activation throughout the human brain in terms of the blood oxygenation level dependent (BOLD) response, there is currently no way to estimate the underlying neural signal dynamics in generating the BOLD response in each local activation region (except for processes slower than the BOLD time course). Knowledge of the neural signal is critical if spatial mapping is to progress to the analysis of dynamic information flow through the cortical networks as the brain performs its tasks. We introduce an analytic approach that provides a new level of conceptualization and specificity in the study of brain processing by non-invasive methods. This technique allows us to use brain imaging methods to determine the dynamics of local neural population responses to their native temporal resolution throughout the human brain, with relatively narrow confidence intervals on many response properties. The ability to characterize local neural dynamics in the human brain represents a significant enhancement of brain imaging capabilities, with potential applications ranging from general cognitive studies to assessment of neuropathologies.

Youth at risk for obesity show greater activation of striatal and somatosensory regions to food

Obese humans, compared with normal-weight humans, have less striatal D2 receptors and striatal response to food intake; weaker striatal response to food predicts weight gain for individuals at genetic risk for reduced dopamine (DA) signaling, consistent with the reward-deficit theory of obesity. Yet these may not be initial vulnerability factors, as overeating reduces D2 receptor density, D2 sensitivity, reward sensitivity, and striatal response to food. Obese humans also show greater striatal, amygdalar, orbitofrontal cortex, and somatosensory region response to food images than normal-weight humans do, which predicts weight gain for those not at genetic risk for compromised dopamine signaling, consonant with the reward-surfeit theory of obesity. However, after pairings of palatable food intake and predictive cues, DA signaling increases in response to the cues, implying that eating palatable food contributes to increased responsivity. Using fMRI, we tested whether normal-weight adolescents at high- versus low-risk for obesity showed aberrant activation of reward circuitry in response to receipt and anticipated receipt of palatable food and monetary reward. High-risk youth showed greater activation in the caudate, parietal operculum, and frontal operculum in response to food intake and in the caudate, putamen, insula, thalamus, and orbitofrontal cortex in response to monetary reward. No differences emerged in response to anticipated food or monetary reward. Data indicate that youth at risk for obesity show elevated reward circuitry responsivity in general, coupled with elevated somatosensory region responsivity to food, which may lead to overeating that produces blunted dopamine signaling and elevated responsivity to food cues.

Spatially extended FMRI signal response to stimulus in non-functionally relevant regions of the human brain: preliminary results

The blood-oxygenation level dependent (BOLD) haemodynamic response function (HDR) in functional magnetic resonance imaging (fMRI) is a delayed and indirect marker of brain activity. In this single case study a small BOLD response synchronised with the stimulus paradigm is found globally, i.e. in all areas outside those of expected activation in a single subject study. The nature of the global response has similar shape properties to the archetypal BOLD HDR, with an early positive signal and a late negative response typical of the negative overshoot. Fitting Poisson curves to these responses showed that voxels were potentially split into two sets: one with dominantly positive signal and the other predominantly negative. A description, quantification and mapping of the global BOLD response is provided along with a 2 × 2 classification table test to demonstrate existence with very high statistical confidence. Potential explanations of the global response are proposed in terms of 1) global HDR balancing; 2) resting state network modulation; and 3) biological systems synchronised with the stimulus cycle. Whilst these widespread and low-level patterns seem unlikely to provide additional information for determining activation in functional neuroimaging studies as conceived in the last 15 years, knowledge of their properties may assist more comprehensive accounts of brain connectivity in the future.

An fMRI study of obesity, food reward, and perceived caloric density. Does a low-fat label make food less appealing?

We tested the hypothesis that obese individuals experience greater activation of the gustatory and somatosensory cortex, but weaker activation of the striatum, in response to intake and anticipated intake of high-fat chocolate milkshake versus an isocaloric milkshake labeled low-fat and a tasteless solution using functional magnetic resonance imaging (fMRI) with 17 obese and 17 lean young women. Obese relative to lean women showed greater activation in somatosensory (Rolandic operculum), gustatory (frontal operculum), and reward valuation regions (amgydala, ventralmedial prefrontal cortex (vmPFC) in response to intake and anticipated intake of milkshake versus tasteless solution, though there was little evidence of reduced striatal activation. Obese relative to lean women also showed greater activation in the Rolandic operculum, frontal operculum, and vmPFC in response to isocaloric milkshakes labeled regular versus low-fat. Results suggest that hyper-responsivity of somatosensory, gustatory, and reward valuation regions may be related to overeating and that top-down processing influence reward encoding, which could further contribute to weight gain.

Neural correlates of food addiction

CONTEXT

Research has implicated an addictive process in the development and maintenance of obesity. Although parallels in neural functioning between obesity and substance dependence have been found, to our knowledge, no studies have examined the neural correlates of addictive-like eating behavior.

OBJECTIVE

To test the hypothesis that elevated "food addiction" scores are associated with similar patterns of neural activation as substance dependence.

DESIGN

Between-subjects functional magnetic resonance imaging study.

SETTING

A university neuroimaging center.

PARTICIPANTS

Forty-eight healthy young women ranging from lean to obese recruited for a healthy weight maintenance trial.

MAIN OUTCOME MEASURE

The relation between elevated food addiction scores and blood oxygen level-dependent functional magnetic resonance imaging activation in response to receipt and anticipated receipt of palatable food (chocolate milkshake).

RESULTS

Food addiction scores (N = 39) correlated with greater activation in the anterior cingulate cortex, medial orbitofrontal cortex, and amygdala in response to anticipated receipt of food (P < .05, false discovery rate corrected for multiple comparisons in small volumes). Participants with higher (n = 15) vs lower (n = 11) food addiction scores showed greater activation in the dorsolateral prefrontal cortex and the caudate in response to anticipated receipt of food but less activation in the lateral orbitofrontal cortex in response to receipt of food (false discovery rate-corrected P < .05).

CONCLUSIONS

Similar patterns of neural activation are implicated in addictive-like eating behavior and substance dependence: elevated activation in reward circuitry in response to food cues and reduced activation of inhibitory regions in response to food intake.

Time course and spatial distribution of fMRI signal changes during single-pulse transcranial magnetic stimulation to the primary motor cortex

Simultaneous transcranial magnetic stimulation (TMS) and functional magnetic resonance imaging (fMRI) may advance the understanding of neurophysiological mechanisms of TMS. However, it remains unclear if TMS induces fMRI signal changes consistent with the standard hemodynamic response function (HRF) in both local and remote regions. To address this issue, we delivered single-pulse TMS to the left M1 during simultaneous recoding of electromyography and time-resolved fMRI in 36 healthy participants. First, we examined the time-course of fMRI signals during supra- and subthreshold single-pulse TMS in comparison with those during voluntary right hand movement and electrical stimulation to the right median nerve (MNS). All conditions yielded comparable time-courses of fMRI signals, showing that HRF would generally provide reasonable estimates for TMS-evoked activity in the motor areas. However, a clear undershoot following the signal peak was observed only during subthreshold TMS in the left M1, suggesting a small but meaningful difference between the locally and remotely TMS-evoked activities. Second, we compared the spatial distribution of activity across the conditions. Suprathreshold TMS-evoked activity overlapped not only with voluntary movement-related activity but also partially with MNS-induced activity, yielding overlapped areas of activity around the stimulated M1. The present study has provided the first experimental evidence that motor area activity during suprathreshold TMS likely includes activity for processing of muscle afferents. A method should be developed to control the effects of muscle afferents for fair interpretation of TMS-induced motor area activity during suprathreshold TMS to M1.

Relation of dietary restraint scores to activation of reward-related brain regions in response to food intake, anticipated intake, and food pictures

Prospective studies indicate that individuals with elevated dietary restraint scores are at increased risk for future bulimic symptom onset, suggesting that these individuals may show hyper-responsivity of reward regions to food and food cues. Thus, we used functional magnetic resonance imaging (fMRI) to examine the relation of dietary restraint scores to activation of reward-related brain regions in response to receipt and anticipated receipt of chocolate milkshake and exposure to pictures of appetizing foods in 39 female adolescents (mean age=15.5 ± 0.94). Dietary restraint scores were positively correlated with activation in the right orbitofrontal cortex (OFC) and bilateral dorsolateral prefrontal cortex (DLPFC) in response to milkshake receipt. However, dietary restraint scores did not correlate with activation in response to anticipated milkshake receipt or exposure to food pictures. Results indicate that individuals who report high dietary restraint have a hyper-responsivity in reward-related brain regions when food intake is occurring, which may increase risk for overeating and binge eating.

Task relevance modulates successful retrieval effects during explicit and implicit memory tests

The successful retrieval effect refers to greater activation for items identified as old compared to those identified as new. This effect is particularly apparent in the ventral posterior parietal cortex (vPPC), though its functional properties remain unclear. In two experiments, we assessed the activation for old and new items during explicit and implicit tests of memory. In Experiment 1, significant effects were observed during explicit recognition performance and during an implicit lexical decision task. In both tasks, determining mnemonic status provides relevant information to task goals. Experiment 2 included a second implicit task in which determining mnemonic status was not relevant (color discrimination task). In this case, vPPC activation did not distinguish between old and new items. These findings suggest that automatic or implicit processes can drive retrieval-related activation in the vPPC, though such processes are gated by stimulus relevancy and task goals.

Latencies in BOLD response during visual attention processes

One well-investigated division of attentional processes focuses on alerting, orienting and executive control, which can be assessed applying the attentional network test (ANT). The goal of the present study was to add further knowledge about the temporal dynamics of relevant neural correlates. As a right hemispheric dominance for alerting and orienting has previously been reported for intrinsic but not for phasic alertness, we additionally addressed a potential impact of this lateralization of attention by employing a lateralized version of the ANT, capturing phasic alertness processes. Sixteen healthy subjects underwent event-related functional magnetic resonance imaging (fMRI) while performing the ANT. Analyses of BOLD magnitude replicated the engagement of a fronto-parietal network in the attentional subsystems. The amplitudes of the attentional contrasts interacted with visual field presentation in the sense that the thalamus revealed a greater involvement for spatially cued items presented in the left visual field. Comparisons of BOLD latencies in visual cortices, first, verified faster BOLD responses following contra-lateral stimulus presentation. Second and more importantly, we identified attention-modulated activation in secondary visual and anterior cingulate cortices. Results are discussed in terms of bottom-up and lateralization processes. Although intrinsic and phasic alertness are distinct cognitive processes, we propose that neural substrates of intrinsic alertness may be accessed by phasic alertness provided that the attention-dominant (i.e., the right) hemisphere is activated directly by a warning stimulus.

The neural correlates of visual working memory encoding: a time-resolved fMRI study

The encoding of information into visual working memory (VWM) is not only a prerequisite step for efficient working memory, it is also considered to limit our ability to attend to, and be consciously aware of, task-relevant events. Despite its important role in visual cognition, the neural mechanisms underlying visual working memory encoding have not yet been specifically dissociated from those involved in perception and/or VWM maintenance. To isolate the brain substrates supporting VWM encoding, here we sought to identify, with time-resolved fMRI, brain regions whose temporal profile of activation tracked the time course of VWM encoding. We applied this approach to two different stimulus categories - colors and faces - that dramatically differ in their encoding time. While several cortical and subcortical regions were activated during the VWM encoding period, one of these regions in the lateral prefrontal cortex - the inferior frontal junction - showed a temporal activation profile associated with the duration of encoding and that could not be accounted for by either perceptual or general attentional effects. Moreover, this region corresponds to the prefrontal area previously implicated in 'attentional blink' paradigms demonstrating attentional limits to conscious perception. These results not only suggest that the inferior frontal junction is involved in VWM encoding, they also provide neural support for theories positing that VWM encoding is a rate-limiting process underlying our attentional limits to visual awareness.

Electrophysiology meets fMRI: neural correlates of the startle reflex assessed by simultaneous EMG-fMRI data acquisition

The startle reflex provides a unique tool for the investigation of sensorimotor gating and information processing. Simultaneous EMG-fMRI acquisition (i.e., online stimulation and recording in the MR environment) allows for the quantitative assessment of the neuronal correlates of the startle reflex and its modulations on a single trial level. This serves as the backbone for a startle response informed fMRI analysis, which is fed by data acquired in the same brain at the same time. We here present the first MR study using a single trial approach with simultaneous acquired EMG and fMRI data on the human startle response in 15 healthy young men. It investigates the neural correlates for isolated air puff startle pulses (PA), prepulse-pulse inhibition (PPI), and prepulse facilitation (PPF). We identified a common core network engaged by all three conditions (PA, PPI, and PPF), consisting of bilateral primary and secondary somatosensory cortices, right insula, right thalamus, right temporal pole, middle cingulate cortex, and cerebellum. The cerebellar vermis exhibits distinct activation patterns between the startle modifications. It is differentially activated with the highest amplitude for PPF, a lower activation for PA, and lowest for PPI. The orbital frontal cortex exhibits a differential activation pattern, not for the type of startle response but for the amplitude modification. For pulse alone it is close to zero; for PPI it is activated. This is in contrast to PPF where it shows deactivation. In addition, the thalamus, the cerebellum, and the anterior cingulate cortex add to the modulation of the startle reflex.

Weight gain is associated with reduced striatal response to palatable food

Consistent with the theory that individuals with hypofunctioning reward circuitry overeat to compensate for a reward deficit, obese versus lean humans have fewer striatal D2 receptors and show less striatal response to palatable food intake. Low striatal response to food intake predicts future weight gain in those at genetic risk for reduced signaling of dopamine-based reward circuitry. Yet animal studies indicate that intake of palatable food results in downregulation of D2 receptors, reduced D2 sensitivity, and decreased reward sensitivity, implying that overeating may contribute to reduced striatal responsivity. Thus, we tested whether overeating leads to reduced striatal responsivity to palatable food intake in humans using repeated-measures functional magnetic resonance imaging. Results indicated that women who gained weight over a 6 month period showed a reduction in striatal response to palatable food consumption relative to weight-stable women. Collectively, results suggest that low sensitivity of reward circuitry increases risk for overeating and that this overeating may further attenuate responsivity of reward circuitry in a feedforward process.

A statistical framework for optimal design matrix generation with application to fMRI

The general linear model (GLM) is a well established tool for analyzing functional magnetic resonance imaging (fMRI) data. Most fMRI analyses via GLM proceed in a massively univariate fashion where the same design matrix is used for analyzing data from each voxel. A major limitation of this approach is the locally varying nature of signals of interest as well as associated confounds. This local variability results in a potentially large bias and uncontrolled increase in variance for the contrast of interest. The main contributions of this paper are two fold: 1) we develop a statistical framework that enables estimation of an optimal design matrix while explicitly controlling the bias variance decomposition over a set of potential design matrices and 2) we develop and validate a numerical algorithm for computing optimal design matrices for general fMRI data sets. The implications of this framework include the ability to match optimally the magnitude of underlying signals to their true magnitudes while also matching the "null" signals to zero size thereby optimizing both the sensitivity and specificity of signal detection. By enabling the capture of multiple profiles of interest using a single contrast (as opposed to an F-test) in a way that optimizes for both bias and variance enables the passing of first level parameter estimates and their variances to the higher level for group analysis which is not possible using F-tests. We demonstrate the application of this approach to in vivo pharmacological fMRI data capturing the acute response to a drug infusion, to task-evoked, block design fMRI and to the estimation of a haemodynamic response function (HRF) in event-related fMRI. Although developed with motivation from fMRI, our framework is quite general and has potentially wide applicability to a variety of disciplines.

The insular taste cortex contributes to odor quality coding

Despite distinct peripheral and central pathways, stimulation of both the olfactory and the gustatory systems may give rise to the sensation of sweetness. Whether there is a common central mechanism producing sweet quality sensations or two discrete mechanisms associated independently with gustatory and olfactory stimuli is currently unknown. Here we used fMRI to determine whether odor sweetness is represented in the piriform olfactory cortex, which is thought to code odor quality, or in the insular taste cortex, which is thought to code taste quality. Fifteen participants sampled two concentrations of a pure sweet taste (sucrose), two sweet food odors (chocolate and strawberry), and two sweet floral odors (lilac and rose). Replicating prior work we found that olfactory stimulation activated the piriform, orbitofrontal and insular cortices. Of these regions, only the insula also responded to sweet taste. More importantly, the magnitude of the response to the food odors, but not to the non-food odors, in this region of insula was positively correlated with odor sweetness rating. These findings demonstrate that insular taste cortex contributes to odor quality coding by representing the taste-like aspects of food odors. Since the effect was specific to the food odors, and only food odors are experienced with taste, we suggest this common central mechanism develops as a function of experiencing flavors.

The interrelations between verbal working memory and visual selection of emotional faces

Working memory (WM) and visual selection processes interact in a reciprocal fashion based on overlapping representations abstracted from the physical characteristics of stimuli. Here, we assessed the neural basis of this interaction using facial expressions that conveyed emotion information. Participants memorized an emotional word for a later recognition test and then searched for a face of a particular gender presented in a display with two faces that differed in gender and expression. The relation between the emotional word and the expressions of the target and distractor faces was varied. RTs for the memory test were faster when the target face matched the emotional word held in WM (on valid trials) relative to when the emotional word matched the expression of the distractor (on invalid trials). There was also enhanced activation on valid compared with invalid trials in the lateral orbital gyrus, superior frontal polar (BA 10), lateral occipital sulcus, and pulvinar. Re-presentation of the WM stimulus in the search display led to an earlier onset of activity in the superior and inferior frontal gyri and the anterior hippocampus irrespective of the search validity of the re-presented stimulus. The data indicate that the middle temporal and prefrontal cortices are sensitive to the reappearance of stimuli that are held in WM, whereas a fronto-thalamic occipital network is sensitive to the behavioral significance of the match between WM and targets for selection. We conclude that these networks are modulated by high-level matches between the contents of WM, behavioral goals, and current sensory input.

Body mass correlates inversely with inhibitory control in response to food among adolescent girls: an fMRI study

Self-report and behavioral data suggest that impulsivity may contribute to the development and maintenance of obesity. Neuroimaging studies implicate a widespread neural network in inhibitory control and suggest that impulsive individuals show hypoactivity in these regions during tasks requiring response inhibition. Yet, research has not directly tested whether body mass correlates inversely with activation of these regions during response inhibition tasks. The present study used functional magnetic resonance imaging (fMRI) to investigate neural activations during a food-specific go/no-go task in adolescent girls ranging from lean to obese. When required to inhibit prepotent responses to appetizing food, body mass index (BMI) correlated with response inhibition at both the behavioral and neural levels, with more overweight adolescents showing greater behavioral evidence of impulsivity as well as reduced activation of frontal inhibitory regions, including superior frontal gyrus, middle frontal gyrus, ventrolateral prefrontal cortex, medial prefrontal cortex, and orbitofrontal cortex, than leaner individuals. As well, activation in food reward regions (e.g., temporal operculum/insula) in response to food images correlated positively with BMI. Results suggest that hypofunctioning of inhibitory control regions and increased response of food reward regions are related to elevated weight.

Functional MRI and multivariate autoregressive models

Connectivity refers to the relationships that exist between different regions of the brain. In the context of functional magnetic resonance imaging (fMRI), it implies a quantifiable relationship between hemodynamic signals from different regions. One aspect of this relationship is the existence of small timing differences in the signals in different regions. Delays of 100 ms or less may be measured with fMRI, and these may reflect important aspects of the manner in which brain circuits respond as well as the overall functional organization of the brain. The multivariate autoregressive time series model has features to recommend it for measuring these delays and is straightforward to apply to hemodynamic data. In this review, we describe the current usage of the multivariate autoregressive model for fMRI, discuss the issues that arise when it is applied to hemodynamic time series and consider several extensions. Connectivity measures like Granger causality that are based on the autoregressive model do not always reflect true neuronal connectivity; however, we conclude that careful experimental design could make this methodology quite useful in extending the information obtainable using fMRI.

fMRI responses to words repeated in a congruous semantic context are abnormal in mild Alzheimer's disease

BACKGROUND

We adapted an event-related brain potential word repetition paradigm, sensitive to early Alzheimer's disease (AD), for functional MRI (fMRI). We hypothesized that AD would be associated with reduced differential response to New/Old congruous words.

METHODS

Fifteen mild AD patients (mean age=72.9) and 15 normal elderly underwent 1.5T fMRI during a semantic category decision task.

RESULTS

We found robust between-groups differences in BOLD response to congruous words. In controls, the New>Old contrast demonstrated larger responses in much of the left-hemisphere (including putative P600 generators: parahippocampal, cingulate, fusiform, perirhinal, middle temporal (MTG) and inferior frontal gyri (IFG)); the Old>New contrast showed modest activation, mainly in right parietal and prefrontal cortex. By contrast, there were relatively few regions of significant New>Old responses in AD patients, mainly in the right-hemisphere, and their Old>New contrast did not demonstrate a right-hemisphere predominance. Across subjects, the spatial extent of New>Old responses in left medial temporal lobe (MTL) correlated with subsequent recall and recognition (r's>or=0.60). In controls, the magnitude of New-Old response in left MTL, fusiform, IFG, MTG, superior temporal and cingulate gyrus correlated with subsequent cued recall and/or recognition (0.51<or=r's<or=0.78).

CONCLUSIONS

A distributed network of mostly left-hemisphere structures, which are putative P600 generators, appears important for successful verbal encoding (with New>Old responses to congruous words in normal elderly). This network appears dysfunctional in mild AD patients, as reflected in decreased word repetition effects particularly in left association cortex, paralimbic and MTL structures.

Spatially adaptive mixture modeling for analysis of FMRI time series

Within-subject analysis in fMRI essentially addresses two problems, the detection of brain regions eliciting evoked activity and the estimation of the underlying dynamics. In Makni et aL, 2005 and Makni et aL, 2008, a detection-estimation framework has been proposed to tackle these problems jointly, since they are connected to one another. In the Bayesian formalism, detection is achieved by modeling activating and nonactivating voxels through independent mixture models (IMM) within each region while hemodynamic response estimation is performed at a regional scale in a nonparametric way. Instead of IMMs, in this paper we take advantage of spatial mixture models (SMM) for their nonlinear spatial regularizing properties. The proposed method is unsupervised and spatially adaptive in the sense that the amount of spatial correlation is automatically tuned from the data and this setting automatically varies across brain regions. In addition, the level of regularization is specific to each experimental condition since both the signal-to-noise ratio and the activation pattern may vary across stimulus types in a given brain region. These aspects require the precise estimation of multiple partition functions of underlying Ising fields. This is addressed efficiently using first path sampling for a small subset of fields and then using a recently developed fast extrapolation technique for the large remaining set. Simulation results emphasize that detection relying on supervised SMM outperforms its IMM counterpart and that unsupervised spatial mixture models achieve similar results without any hand-tuning of the correlation parameter. On real datasets, the gain is illustrated in a localizer fMRI experiment: brain activations appear more spatially resolved using SMM in comparison with classical general linear model (GLM)-based approaches, while estimating a specific parcel-based HRF shape. Our approach therefore validates the treatment of unsmoothed fMRI data without fixed GLM definition at the subject level and makes also the classical strategy of spatial Gaussian filtering deprecated.

Reward circuitry responsivity to food predicts future increases in body mass: moderating effects of DRD2 and DRD4

OBJECTIVE

To determine whether responsivity of reward circuitry to food predicts future increases in body mass and whether polymorphisms in DRD2 and DRD4 moderate these relations.

DESIGN

The functional magnetic resonance imaging (fMRI) paradigm investigated blood oxygen level dependent activation in response to imagined intake of palatable foods, unpalatable foods, and glasses of water shown in pictures. DNA was extracted from saliva samples using standard salting-out and solvent precipitation methods.

PARTICIPANTS

Forty-four adolescent female high school students ranging from lean to obese.

MAIN OUTCOME

Future increases in body mass index (BMI).

RESULTS

Weaker activation of the frontal operculum, lateral orbitofrontal cortex, and striatum in response to imagined intake of palatable foods, versus imagined intake of unpalatable foods or water, predicted future increases in body mass for those with the DRD2 TaqIA A1 allele or the DRD4-7R allele. Data also suggest that for those lacking these alleles, greater responsivity of these food reward regions predicted future increases in body mass.

DISCUSSION

This novel prospective fMRI study indicates that responsivity of reward circuitry to food increases risk for future weight gain, but that genes that impact dopamine signaling capacity moderate the predictive effects, suggesting two qualitatively distinct pathways to unhealthy weight gain based on genetic risk.

Thalamic pathology in schizophrenia

The thalamus plays a critical role in the coordination of information as it passes from region to region within the brain. A disruption of that information flow may give rise to some of the cardinal symptoms of schizophrenia. In support of this hypothesis, schizophrenia-like syndromes emerge when illnesses, such as stroke, selectively damage the thalamus while sparing the rest of the brain. Evidence from many sources has implicated thalamic dysfunction in schizophrenia. In postmortem studies, several subregions of the thalamus, including the mediodorsal nucleus and the pulvinar, have been shown to have fewer neurons in schizophrenia. Neurochemical disturbances are also seen, with changes in both the glutamate and dopamine systems; thalamic glutamate receptor expression is altered in schizophrenia, and dopamine appears to be elevated in thalamic subregions, while evidence exists of an imbalance between dopamine and other neurotransmitters. In vivo studies using magnetic resonance imaging have demonstrated smaller thalamic volumes in schizophrenia, as well as shape deformations suggesting changes in those thalamic regions that are most densely connected to the portions of the brain responsible for executive function and sensory integration. These changes seem to be correlated with clinical symptoms. The thalamus is a starting point for several parallel, overlapping networks that extend from thalamic nuclei to the cortex. Evidence is emerging that changes in the thalamic nodes of these networks are echoed by changes at other points along the chain; this suggests that schizophrenia might be a disease of disrupted thalamocortical neural networks. This model distributes the pathology throughout the network, but also concentrates attention on the thalamus as a critical structure, especially because of its role in coordinating the flow of information within and between neural networks.

Group specific optimisation of fMRI processing steps for child and adult data

Motion is a major issue in functional magnetic resonance imaging (fMRI) dataseries and causes artifacts or increased overall noise obscuring signals of interest. It is particularly important to be able to control for and correct these artifacts when dealing with child data. We analysed the data from 35 children (4-8 years old) and 13 adults (18-30 years old) during an emotional face paradigm. The children were split into low and high motion groups on the basis of having less or more than an estimated maximal movement of one voxel (3.75 mm) and one degree of rotation in any motion direction between any pair of scans in the run. Several different preprocessing steps were evaluated for their ability to correct for the excess motion using agnostic canonical variates analysis (aCVA) in the NPAIRS (Nonparametric, Prediction, Activation, Influence, Reproducibility, re-Sampling) framework. The adult dataset was reasonably stable whereas the motion-prone child datasets benefited greatly from motion parameter regression (MPR). Motion parameter regression had a strong beneficial impact on all datasets, a result that was largely unaffected by other preprocessing choices; however, motion correction on its own did not have as much impact. The low motion child group subjected to MPR had reproducibility values at par with those of the adult group, but needed almost twice as many subjects to achieve this result, indicating weaker responses in young children. The aCVA showed greater sensitivity to the task response pattern than the mixed effects general linear model (mGLM) in the expected face processing regions, although the mGLM showed more responses in some other areas. This work illustrates that preprocessing choices must be made in a group-specific fashion to optimise fMRI results.

Where is the semantic system? A critical review and meta-analysis of 120 functional neuroimaging studies

Semantic memory refers to knowledge about people, objects, actions, relations, self, and culture acquired through experience. The neural systems that store and retrieve this information have been studied for many years, but a consensus regarding their identity has not been reached. Using strict inclusion criteria, we analyzed 120 functional neuroimaging studies focusing on semantic processing. Reliable areas of activation in these studies were identified using the activation likelihood estimate (ALE) technique. These activations formed a distinct, left-lateralized network comprised of 7 regions: posterior inferior parietal lobe, middle temporal gyrus, fusiform and parahippocampal gyri, dorsomedial prefrontal cortex, inferior frontal gyrus, ventromedial prefrontal cortex, and posterior cingulate gyrus. Secondary analyses showed specific subregions of this network associated with knowledge of actions, manipulable artifacts, abstract concepts, and concrete concepts. The cortical regions involved in semantic processing can be grouped into 3 broad categories: posterior multimodal and heteromodal association cortex, heteromodal prefrontal cortex, and medial limbic regions. The expansion of these regions in the human relative to the nonhuman primate brain may explain uniquely human capacities to use language productively, plan, solve problems, and create cultural and technological artifacts, all of which depend on the fluid and efficient retrieval and manipulation of semantic knowledge.

Investigating hemodynamic response variability at the group level using basis functions

Introduced is a general framework for performing group-level analyses of fMRI data using any basis set of two functions (i.e., the canonical hemodynamic response function and its first derivative) to model the hemodynamic response to neural activity. The approach allows for flexible implementation of physiologically based restrictions on the results. Information from both basis functions is used at the group level and the limitations avoid physiologically ambiguous or implausible results. This allows for investigation of specific BOLD activity such as hemodynamic responses peaking within a specified temporal range (i.e., 4-5 s). The general nature of the presented approach allows for applications using basis sets specifically designed to investigate various physiologic phenomena, i.e., age-related variability in poststimulus undershoot, hemodynamic responses measured with cerebral blood flow imaging, or subject-specific basis sets. An example using data from a group of healthy young participants demonstrates the methods and the specific steps to study poststimulus variability are discussed. The approach is completely implemented within the general linear model and requires minimal programmatic calculations.

Involvement of the thalamocortical loop in the spontaneous switching of percepts in auditory streaming

Perceptual grouping of successive frequency components, namely, auditory streaming, is essential for auditory scene analysis. Prolonged listening to an unchanging triplet-tone sequence produces a series of illusory switches between a single coherent stream (S1) and two distinct streams (S2). The predominant percept depends on the frequency difference (Deltaf) between high and low tones. Here, we combined the use of different Deltafs with an event-related fMRI design to identify whether the temporal dynamics of brain activity differs depending on the direction of perceptual switches. The results demonstrated that the activity of the medial geniculate body (MGB) in the thalamus occurred earlier during switching from nonpredominant to predominant percepts, whereas that of the auditory cortex (AC) occurred earlier during switching from predominant to nonpredominant percepts, regardless of Deltaf. The asymmetry of temporal precedence indicates that the MGB and AC activations play different roles in perceptual switching and depend on perceptual predominance rather than on S1 and S2 percepts per se. Our results suggest that feedforward and feedback processes in the thalamocortical loop are involved in the formation of percepts in auditory streaming.

Robust and unbiased variance of GLM coefficients for misspecified autocorrelation and hemodynamic response models in fMRI

As a consequence of misspecification of the hemodynamic response and noise variance models, tests on general linear model coe cients are not valid. Robust estimation of the variance of the general linear model (GLM) coecients in fMRI time series is therefore essential. In this paper an alternative method to estimate the variance of the GLM coe cients accurately is suggested and compared to other methods. The alternative, referred to as the sandwich, is based primarily on the fact that the time series are obtained from multiple exchangeable stimulus presentations. The analytic results show that the sandwich is unbiased. Using this result, it is possible to obtain an exact statistic which keeps the 5% false positive rate. Extensive Monte Carlo simulations show that the sandwich is robust against misspeci cation of the autocorrelations and of the hemodynamic response model. The sandwich is seen to be in many circumstances robust, computationally efficient, and flexible with respect to correlation structures across the brain. In contrast, the smoothing approach can be robust to a certain extent but only with specific knowledge of the circumstances for the smoothing parameter.