Event-related Functional MRI Research Articles

Repetition suppression of faces is modulated by emotion.

Single-unit recordings and functional brain imaging studies have shown reduced neural responses to repeated stimuli in the visual cortex. By using event-related functional MRI, we compared the activation evoked by repetitions of neutral and fearful faces, which were either task relevant (targets) or irrelevant (distracters). We found that within the inferior occipital gyri, lateral fusiform gyri, superior temporal sulci, amygdala, and the inferior frontal gyri/insula, targets evoked stronger responses than distracters and their repetition was associated with significantly reduced responses. Repetition suppression, as manifested by the difference in response amplitude between the first and third repetitions of a target, was stronger for fearful than neutral faces. Distracter faces, regardless of their repetition or valence, evoked negligible activation, indicating top-down attenuation of behaviorally irrelevant stimuli. Our findings demonstrate a three-way interaction between emotional valence, repetition, and task relevance and suggest that repetition suppression is influenced by high-level cognitive processes in the human brain.

Using visual advance information: an event-related functional MRI study

Our event-related functional MRI (efMRI) study investigates whether visual advance information (AI) affects rather perceptual or central response-related processing areas. Twelve subjects were required to make a go/no-go decision to a conjunction of a specific color and motion direction. The stimuli were preceded by a cue, providing 100% valid advance information about motion direction. Partial and full advance information (PAI and FAI) predicted possible targets, respectively, certain nontargets, neutral cues (NAI) gave no prediction. The time between cue and stimulus (stimulus onset asynchrony, SOA) was varied. A response benefit was found after PAI as compared with NAI. The benefit was small with a short SOA (150 ms), increased with intermediate SOA (450 ms) and sustained with long SOA (750 ms). Perceptual and central processing areas were more active with increasing SOA, but only central response-related processing areas were selectively modulated by cue information. In particular, supplementary motor area and bilateral inferior parietal lobe were more active with PAI than with NAI. If comparing NAI with FAI, more errors were made and activity was larger in central processing areas. Our results suggest that, depending on the processing time, cues providing perceptual information modulate central response-related processes.

Do women with fragile X syndrome have problems in switching attention: Preliminary findings from ERP and fMRI

Fragile X syndrome (FXS) is a neurodevelopmental disorder that represents the most common known cause of developmental delay. Recent neuropsychological findings indicate that females with FXS present with a specific pattern of cognitive deficits and that these difficulties primarily involve skills requiring executive control. The present study is the first to examine the extent to which neural activity of females with FXS can be observed on a task that specifically taps two core deficits, namely switching and response inhibition. Brain activity was measured using both event-related electrical potentials (ERPs) and event-related functional MRI (fMRI) neuroimaging in separate studies using the same cognitive paradigm. Compared to controls, females with FXS were significantly slower and made more errors on trials that required an immediate response (Go) to stimulus onset but were comparable on trials that required a delayed response (Wait) to stimulus onset. At the brain level, several areas showed significantly greater activation for females with FXS compared with controls, including the cingulate cortex and left and right ventral prefrontal areas. In contrast, no areas were found to show significantly greater activation for controls compared with females with FXS.

Functional-anatomic correlates of remembering and knowing

Neural correlates of remembering were examined using event-related functional MRI (fMRI) in 20 young adults. A recognition paradigm based on the remember/know (RK) procedure was used to separately classify studied items that were correctly identified and accompanied by a conscious recollection of details about the study episode from studied items that were correctly identified in the absence of conscious recollection. To facilitate exploration of the basis of remember decisions, studied items were paired with pictures and sounds to encourage retrieval of specific content during scanned testing. Analyses using a priori regions of interest indicated that remembering recruited both regions that associate with the perception and/or decision that information is old and regions that associate preferentially with visual content, while knowing recruited regions associated with oldness, but did not recruit visual content regions. Exploratory analyses further indicated a functional dissociation across regions of parietal cortex that may aid to reconcile several divergent results in the literature. Lateral parietal regions responded preferentially to remember decisions, while a slightly medial region responded robustly to both remember and know decisions. Taken collectively, these results suggest that remembering and knowing associate with common processes supporting a perception and/or the decision that information is old. Remembering additionally recruits regions specific to retrieved content, which may participate to convey the vividness typical of recollective experience.

Temporal resolving power of perfusion- and BOLD-based event-related functional MRI.

Functional magnetic resonance imaging (fMRI) based on both perfusion and blood oxygenation level-dependent (BOLD) contrasts has been widely applied in spatiotemporal mapping of the human brain function. Temporal resolving power of fMRI is limited by the smoothed hemodynamic response function dispersed from the neuronal activity. In this study, temporal modulation transfer functions were utilized to quantify the resolving powers of perfusion and BOLD fMR signals in time domain. The impulse response function was determined using brief visual stimulations and event-related image acquisition schemes. An important feature of arterial spin labeling techniques is that quantitative perfusion and BOLD signals could be simultaneously acquired. This simultaneous BOLD response may arise from signals that are more proximal to capillary beds, and its temporal resolution may be different from that of the typical BOLD response. Therefore, we assessed and compared the temporal resolving capabilities of perfusion, simultaneous BOLD, and the typical BOLD response obtained from the gradient echo EPI pulse sequence. Full-width-at-half-maximums of perfusion and simultaneous BOLD measurements were significantly smaller than that of BOLD ones (4.3+/- 0.6 s vs 5.5 +/- 0.9 s, p<0.02 and 4.7 +/- 1.3 s vs 5.5 +/- 0.9 s, p<0.01, respectively). The corresponding temporal resolving powers of perfusion and simultaneous BOLD signals were statistically better than that of BOLD signals (0.23 +/- 0.03 Hz vs 0.17 +/- 0.02 Hz, p<0.01 and 0.21 +/- 0.04 Hz vs 0.17 +/- 0.02 Hz, p<0.01, respectively). Our results showed that the typical BOLD response was significantly smoothed from the perfusion response, thus resulting in a degraded temporal resolving power. However, results from the simultaneous BOLD and perfusion measurements were not significantly different. Biophysical implications of the experimental outcomes were further investigated using a computer simulation based on the Balloon model. By fitting the measured data into the model, an apparently longer transit time was obtained for the typical BOLD signal (1.7 s), comparing to that for the simultaneous BOLD one (1.2 s). Therefore, the simultaneous BOLD signal was regarded as less susceptible to the variations from local draining veins. Combining the simulation result with the significantly discrepant resolving powers between the two BOLD signals, we speculated that the blurred effects from large vessels played a predominant role that further reduced the temporal resolution of the BOLD-based fMRI from the perfusion response.

Encoding activity in anterior medial temporal lobe supports subsequent associative recognition

The ability to bind information together, such as linking a name with a face or a car with a parking space, is a vital process in human episodic memory. To identify the neural bases for this binding process, we measured brain activity during a verbal associative encoding task using event-related functional MRI (fMRI), followed by an associative recognition test for the studied word pairs. Analysis of the encoding data sorted by the associative recognition accuracy allowed us to isolate regions involved in successfully creating associations. We found that encoding activity in bilateral anterior medial temporal lobe (MTL) regions was greater for successfully bound pairs, that is, those later recognized as intact, than for all other pairs. These findings provide evidence that the anterior medial temporal lobes support the successful binding of information in memory.

Humor Modulates the Mesolimbic Reward Centers

Humor plays an essential role in many facets of human life including psychological, social, and somatic functioning. Recently, neuroimaging has been applied to this critical human attribute, shedding light on the affective, cognitive, and motor networks involved in humor processing. To date, however, researchers have failed to demonstrate the subcortical correlates of the most fundamental feature of humor—reward. In an effort to elucidate the neurobiological substrate that subserves the reward components of humor, we undertook a high-field (3 Tesla) event-related functional MRI study. Here we demonstrate that humor modulates activity in several cortical regions, and we present new evidence that humor engages a network of subcortical regions including the nucleus accumbens, a key component of the mesolimbic dopaminergic reward system. Further, the degree of humor intensity was positively correlated with BOLD signal intensity in these regions. Together, these findings offer new insight into the neural basis of salutary aspects of humor.

Identifying regional activity associated with temporally separated components of working memory using event-related functional MRI

This study describes the neural circuitry underlying temporally separated components of working memory (WM) performance—stimulus encoding, maintenance of information during a delay, and the response to a probe. While other studies have applied event-related fMRI to separate epochs of WM tasks, this study differs in that it employs a methodology that does not make any a priori assumptions about the shape of the hemodynamic response (HDR). This is important because no one model of the HDR is valid across the range of activated brain regions and stimulus types. Systematic modeling inaccuracies may lead to the misattribution of activity to adjacent events. Twelve healthy subjects performed a numerical version of the Sternberg Item Recognition Paradigm adapted for rapid presentation event-related fMRI. This paradigm emphasized maintenance rather than manipulative WM processes and used a subcapacity WM load. WM trials with different delay lengths were compared to fixation. The HDR of the entire WM trial for each trial type was estimated using a finite impulse response (FIR). Regional activity associated with the Encode, Delay, and Probe epochs was identified using contrasts that were based on the FIR estimates and by examining the HDRs. Each epoch was associated with a distinct but overlapping pattern of regional activity. Activation of the dorsolateral prefrontal cortex, thalamus, and basal ganglia was exclusively associated with the probe. This suggests that frontostriatal neural circuitry participates in selecting an appropriate response based on the contents of WM.

Putting names to faces:: Successful encoding of associative memories activates the anterior hippocampal formation

The ability to form associations between previously unrelated items of information, such as names and faces, is an essential aspect of episodic memory function. The neural substrate that determines success vs. failure in learning these associations remains to be elucidated. Using event-related functional MRI during the encoding of novel face-name associations, we found that successfully remembered face-name pairs showed significantly greater activation in the anterior hippocampal formation bilaterally and left inferior prefrontal cortex, compared to pairs that were forgotten. Functional connectivity analyses revealed significant correlated activity between the right and left hippocampus and neocortical regions during successful, but not attempted, encoding. These findings suggest that anterior regions of the hippocampal formation, in particular, are crucial for successful associative encoding and that the degree of coordination between hippocampal and neocortical activity may predict the likelihood of subsequent memory.

An event-related fMRI investigation of phonological versus semantic short-term memory

Studies with normal and brain damaged subjects have indicated that there are semantic as well as phonological contributions to verbal short-term memory. An event-related functional MRI study was carried out to determine if different brain regions would be activated during the delay period in a phonological vs. a semantic retention task. A recognition probe procedure was used in which memory load and task (i.e. rhyme judgment vs. synonym judgment) were manipulated. A left inferior parietal region overlapping the supramarginal gyrus was more activated in the phonological than the semantic task. A large left inferior and mid-frontal region and another left parietal region showed a load effect that was common to the phonological and semantic tasks. No region showed significantly greater activation in the semantic than the phonological task, though there was a trend towards a more anterior localization of the frontal load effect in the semantic task compared to the phonological task.

Predicting the practice effects on the blood oxygenation level-dependent (BOLD) function of fMRI in a symbolic manipulation task.

Based on adaptive control of thought-rational (ACT-R), a cognitive architecture for cognitive modeling, researchers have developed an information-processing model to predict the blood oxygenation level-dependent (BOLD) response of functional MRI in symbol manipulation tasks. As an extension of this research, the current event-related functional MRI study investigates the effect of relatively extensive practice on the activation patterns of related brain regions. The task involved performing transformations on equations in an artificial algebra system. This paper shows that the base-level activation learning in the ACT-R theory can predict the change of the BOLD response in practice in a left prefrontal region reflecting retrieval of information. In contrast, practice has relatively little effect on the form of BOLD response in the parietal region reflecting imagined transformations to the equation or the motor region reflecting manual programming.

Multiple routes to memory: distinct medial temporal lobe processes build item and source memories.

A central function of memory is to permit an organism to distinguish between stimuli that have been previously encountered and those that are novel. Although the medial temporal lobe (which includes the hippocampus and surrounding perirhinal, parahippocampal, and entorhinal cortices) is known to be crucial for recognition memory, controversy remains regarding how the specific subregions within the medial temporal lobe contribute to recognition. We used event-related functional MRI to examine the relation between activation in distinct medial temporal lobe subregions during memory formation and the ability (i) to later recognize an item as previously encountered (item recognition) and (ii) to later recollect specific contextual details about the prior encounter (source recollection). Encoding activation in hippocampus and in posterior parahippocampal cortex predicted later source recollection, but was uncorrelated with item recognition. In contrast, encoding activation in perirhinal cortex predicted later item recognition, but not subsequent source recollection. These outcomes suggest that the subregions within the medial temporal lobe subserve distinct, but complementary, learning mechanisms.

Dynamic changes in the cerebral metabolic rate of o 2 and oxygen extraction ratio in event-related functional MRI

Dynamic changes in the cerebral metabolic rate of oxygen (CMRO 2) and oxygen extraction ratio (OER) in an event-related functional MRI (ER-fMRI) were measured in this study. Six subjects participated in this study at a magnetic field of 1.9 T. Cerebral blood flow (CBF) and blood oxygenation level-dependent (BOLD) changes were acquired during the brief visual stimulation, and the corresponding changes in CMRO 2 and OER were then determined. The results showed that the maximum relative changes in CMRO 2 and OER were about 10.36 ± 0.85 and −6.54 ± 0.55%, respectively, while the maximum changes in CBF and BOLD were approximately 17.35 ± 1.37 and 1.03 ± 0.06%, respectively. The CBF, CMRO 2, and OER changes reach their maximum approximately 1 s earlier than the BOLD signal change (4.15 ± 0.21, 4.16 ± 0.21, and 4.17 ± 0.21 s vs 5.12 ± 0.24 s after stimulation, P < 0.05).

Frontostriatal system in planning complexity: a parametric functional magnetic resonance version of tower of london task

In the present study, we sought to investigate which brain structures are recruited in planning tasks of increasing complexity. For this purpose, a parametric self-paced pseudo-randomized event-related functional MRI version of the Tower of London task was designed. We tested 22 healthy subjects, enabling assessment of imaging results at a second (random effects) level of analysis. Compared with baseline, planning activity was correlated with increased blood oxygenation level-dependent (BOLD) signal in the dorsolateral prefrontal cortex, striatum, premotor cortex, supplementary motor area, and visuospatial system (precuneus and inferior parietal cortex). Task load was associated with increased activity in these same regions. In addition, increasing task complexity was correlated with activity in the left anterior prefrontal cortex, a region supposed to be specifically involved in third-order higher cognitive functioning.

Modulation of the Lexical–Semantic Network by Auditory Semantic Priming: An Event-Related Functional MRI Study

The current event-related fMRI study specifies the neuroanatomical correlates of semantic priming and differences in semantic relation types using an auditory primed lexical decision task (LDT). Word pairs consisted of different relation types, associations ( key– chain), pure categorical relations ( cow– dog), and unrelated words ( table– window), as well as word–pseudoword ( way– tinne) and pseudoword–pseudoword ( ahurn– döva) pairs. The factor lexical status, i.e., the processing of words compared to pseudowords, was associated with activation in the middle temporal gyri and the left striatum. The factor relatedness, i.e., the contrast between unrelated and related target words, was associated with increased activation of the left inferior frontal gyrus, the deep frontal operculum bilaterally, and the middle frontal gyri. A direct contrast between the two semantic relation types indicated that the processing of purely categorical compared to associative information recruits the right precuneus, the isthmus gyrus cinguli, and the cuneus, suggesting more effortful processing of the former information type. The present data show that the factors lexical status, semantic relatedness, and type of semantic relation in a primed LDT modulate the hemodynamic response in cerebral areas that subserve auditory word recognition and subsequent lexical–semantic processing.

Superior digit memory of abacus experts: an event-related functional MRI study.

Abacus experts exhibit superior short-term memory for digits, but the underlying neurophysiological mechanism remains unknown. Using event-related fMRI, we examined the brain activity of abacus experts and non-experts during the memory retention period of a delayed match-to-sample task using digits as stimuli. In controls, activity was greater in cortical areas related to verbal working memory, including Broca's area. In contrast, in experts, activity was greater in cortical areas related to visuo-spatial working memory, including the bilateral superior frontal sulcus and superior parietal lobule. This provides neurophysiological evidence that abacus experts utilize a visuo-spatial representation for digit memory.

Single-Shot Interleaved Z-Shim EPI with Optimized Compensation for Signal Losses due to Susceptibility-Induced Field Inhomogeneity at 3 T

A new single-shot echo-planar imaging (EPI) sequence with interleaved z-shim and optimized compensation for susceptibility-induced signal loss is proposed in this paper. Experiments on human brain demonstrated that the new method is able to regain signal dropout in brain areas with severe susceptibility-induced local gradients, while its image acquisition speed is comparable to that of conventional single-shot EPI techniques. Significant signal-to-noise ratio improvements were demonstrated in the ventral prefrontal and lateral temporal lobes with the new technique compared to a conventional EPI. Brain activation experiments with a bilateral finger-tapping task were performed with intentionally introduced local gradients near the left sensorimotor cortex, by a small gadolinium (Gd)-doped bottle placed on the left side of the head. The results of the functional experiments showed that the interleaved z-shim EPI sequence effectively recovered the signal loss caused by the Gd-doped bottle and reliably detected activation signals in bilateral sensorimotor regions, while the activation signals on the left side diminished considerably in a conventional EPI technique. The new technique, with the capability of reducing susceptibility artifacts and rapid scanning speed, may be particularly useful for event-related functional MRI experiments in the base of the brain, which are of great importance in neuropsychiatric studies.

Fractionating the neural substrate of cognitive control processes.

Psychological and neurobiological theories of cognitive control must account for flexible, seemless transitions among cognitive operations. When subjects switch between tasks, they must both inhibit the previous task and re-engage in a different task. Inhibition of the disengaged task remains active for a period of time and has to be overcome when re-engaging in the same task. Here we used a task-switching paradigm that allows distinction of two control processes: overcoming the inhibition of a previously performed task when re-engaging it and restarting a sequence of tasks after a period of interruption. Behaviorally, these processes were reflected in the facts that: (i) switching to a recently performed task, that is thus unlikely to have fully recovered from inhibition, takes longer than switching to a task less recently performed and (ii) re-engaging in a sequence of tasks after a period of interruption transiently increases response time. Using event-related functional MRI, we found that these two behavioral effects were accompanied by a double dissociation: the right lateral prefrontal cortex was more activated when switching to a task recently performed compared to a task less recently performed, while the anterior cingulate cortex was recruited when a sequence of tasks was initiated. These results provide insights into the functional organization of the frontal lobe in humans and its role in distinct processes involved in cognitive control.

Similarities and Differences in the Neural Correlates of Episodic Memory Retrieval and Working Memory

Functional neuroimaging studies have shown that different cognitive functions activate overlapping brain regions. An activation overlap may occur because a region is involved in operations tapped by different cognitive functions or because the activated area comprises subregions differentially involved in each of the functions. To investigate these issues, we directly compared brain activity during episodic retrieval (ER) and working memory (WM) using event-related functional MRI (fMRI). ER was investigated with a word recognition test, and WM was investigated with a word delayed-response test. Two-phase trials distinguished between retrieval mode and cue-specific aspects of ER, as well as between encoding/maintenance and retrieval aspects of WM. The results revealed a common fronto-parieto-cerebellar network for ER and WM, as well as subregions differentially involved in each function. Specifically, there were two main findings. First, the results differentiated common and specific subregions within the prefrontal cortex: (i) left dorsolateral areas were recruited by both functions, possibly reflecting monitoring operations; (ii) bilateral anterior and ventrolateral areas were more activated during ER than during WM, possibly reflecting retrieval mode and cue-specific ER operations, respectively; and (iii) left posterior/ventral (Broca's area) and bilateral posterior/dorsal areas were more activated during WM than during ER, possibly reflecting phonological and generic WM operations, respectively. Second, hippocampal and parahippocampal regions were activated not only for ER but also for WM. This result suggests that indexing operations mediated by the medial temporal lobes apply to both long-term and short-term memory traces. Overall, our results show that direct cross-function comparisons are critical to understand the role of different brain regions in various cognitive functions.

Hemispheric asymmetry in human lateral prefrontal cortex during cognitive set shifting.

Functional organization of human cerebral hemispheres is asymmetrically specialized, most typically along a verbal/nonverbal axis. In this event-related functional MRI study, we report another example of the asymmetrical specialization. Set-shifting paradigms derived from the Wisconsin card sorting test were used, where subjects update one behavior to another on the basis of environmental feedback. The cognitive requirements constituting the paradigms were decomposed into two components according to temporal stages of task events. Double dissociation of the component brain activity was found in the three bilateral pairs of regions in the lateral frontal cortex, the right regions being activated during exposure to negative feedback and the corresponding left regions being activated during updating of behavior, to suggest that both hemispheres contribute to cognitive set shifting but in different ways. The asymmetrical hemispheric specialization within the same paradigms further implies an interhemispheric interaction of these task components that achieve a common goal.