Imaging the brain activity changes underlying impaired visuospatial judgments: simultaneous FMRI, TMS, and behavioral studies

Damage to parietal cortex impairs visuospatial judgments. However, it is currently unknown how this damage may affect or indeed be caused by functional changes in remote but interconnected brain regions. Here, we applied transcranial magnetic stimulation (TMS) to the parietal cortices during functional magnetic resonance imaging (fMRI) while participants were solving visuospatial tasks. This allowed us to observe both the behavioral and the neural effects of transient parietal activity disruption in the active healthy human brain. Our results show that right, but not left, parietal TMS impairs visuospatial judgment, induces neural activity changes in a specific right-hemispheric network of frontoparietal regions, and shows significant correlations between the induced behavioral impairment and neural activity changes in both the directly stimulated parietal and remote ipsilateral frontal brain regions. The revealed right-hemispheric neural network effect of parietal TMS represents the same brain areas that are functionally connected during the execution of visuospatial judgments. This corroborates the notion that visuospatial deficits following parietal damage are brought about by a perturbation of activity across a specific frontoparietal network, rather than the lesioned parietal site alone. Our experiments furthermore show how concurrent fMRI and magnetic brain stimulation during active task execution hold the potential to identify and visualize networks of brain areas that are functionally related to specific cognitive processes.     

Distribution of cortical activation during visuospatial n-back tasks as revealed by functional magnetic resonance imaging

Human neuroimaging studies conducted during visuospatial working memory tasks have inconsistently detected activation in the prefrontal cortical areas depending presumably on the type of memory and control tasks employed. We used functional magnetic resonance imaging to study brain activation related to the performance of a visuospatial n-back task with different memory loads (0-back, 1-back and 2-back tasks). Comparison of the 2-back versus 0-back tasks revealed consistent, bilateral activation in the medial frontal gyrus (MFG), superior frontal sulcus and adjacent cortical tissue (SFS/SFG) in all subjects and in six out of seven subjects in the intraparietal sulcus (IPS). Activation was also detected in the inferior frontal gyrus, medially in the superior frontal gyrus, precentral gyrus, superior and inferior parietal lobuli, occipital visual association areas, anterior and posterior cingulate areas and in the insula. Comparison between the 1- back versus 0-back tasks revealed activation only in a few brain areas. Activation in the MFG, SFS/SFG and IPS appeared dependent on memory load. The results suggest that the performance of a visuospatial working memory task engages a network of distributed brain areas and that areas in the dorsal visual pathway are engaged in mnemonic processing of visuospatial information.      

Spatial and Temporal Factors in the Role of Prefrontal and Parietal Cortex in Visuomotor Integration

The effects of reversible lesion—by cooling—of dorsolateralprefrontal and posterior parietal cortex were studied in rhesusmonkeys performing a cognitive visuomotor integration task.Correct performance required the use of a learned set of cue-responsecontingencies, some spatial andsome nonspatial; in some cases,the task required the short-term retention, through a delay,of the color of the cue or its implicit response direction.Prefrontal cooling impaired performance of the task regardlessof its spatial demands, an effect that increased with delay.Parietal cooling, on the other hand, only impaired performanceif the task demanded the processing and retention of spatialinformation (i.e., if spatial active memory was required). Parietaleffects were not related to delay. Both prefrontal and, evenmore, parietal cooling increased response time in all task contingencies.Thus, the results dissociate the respective contributions ofthe prefrontal and the posterior parietal cortex to the temporaland spatial aspects of information processing in visuomotorperformance. They indicate that posterior parietal areas participatein spatial processing and in active memory of spatial information,whereas prefrontal areas subserve a broader role of visuomotorprocessing and cross-temporal integration of both spatial andnonspatial information.     

The neural basis of visual skill learning: an fMRI study of mirror reading

The learning of perceptual skills is thought to rely upon multiple regions in the cerebral cortex, but imaging studies have not yet provided evidence about the changes in neural activity that accompany visual skill learning. Functional magnetic resonance imaging (fMRI) was used to examine changes in activation of posterior brain regions associated with the acquisition of mirror-reading skill for novel and practiced stimuli. Multiple regions in the occipital lobe, inferior temporal cortex, superior parietal cortex and cerebellum were involved in the reading of mirror-reversed compared to normally oriented text. For novel stimuli, skilled mirror-reading was associated with decreased activation in the right superior parietal cortex and posterior occipital regions and increased activation in the left inferior temporal lobe. These results suggest that learning to read mirror- reversed text involves a progression from visuospatial transformation to direct recognition of transformed letters. Reading practiced, relative to unpracticed, stimuli was associated with decreased activation in occipital visual cortices, inferior temporal cortex and superior parietal cortex and increased activation in occipito-parietal and lateral temporal regions. By examining skill learning and item- specific repetition priming in the same task, this study demonstrates that both of these forms of learning exhibit shifts in the set of neural structures that contribute to performance.      

Domain-general and domain-sensitive prefrontal mechanisms for recollecting events and detecting novelty

Recollecting the past and discriminating novel from familiar memoranda depend on poorly understood prefrontal cortical (PFC) mechanisms hypothesized to vary according to memory task (e.g. recollection versus novelty detection) and domain of targeted memories (e.g. perceptual versus conceptual). Using event-related fMRI, we demonstrate that recollecting conceptual or perceptual details surrounding object encounters similarly recruits left frontopolar and posterior PFC compared with detecting novel stimuli, suggesting that a domain-general control network is engaged during contextual remembering. In contrast, left anterior ventrolateral PFC coactivated with a left middle temporal region associated with semantic representation, and right ventrolateral PFC with bilateral occipito-temporal cortices associated with representing object form, depending on whether recollections were conceptual or perceptual. These PFC/posterior cortical dissociations suggest that during recollection, lateralized ventrolateral PFC mechanisms bias posterior conceptual or perceptual feature representations as a function of memory relevance, potentially improving the gain of bottom-up memory signals. Supporting this domain-sensitive biasing hypothesis, novelty detection also recruited right ventrolateral PFC and bilateral occipito-temporal cortices compared with conceptual recollection, suggesting that searching for novel objects heavily relies upon perceptual feature processing. Collectively, these data isolate task- from domain-sensitive PFC control processes strategically recruited in the service of episodic memory.     

Cortical Networks for Visual Reaching: Physiological and Anatomical Organization of Frontal and Parietal Lobe Arm Regions

The functional and structural properties of the dorsolateralfrontal lobe and posterior parietal proximal arm representationswere studied in macaque monkeys. Physiological mapping of primarymotor (MI), dorsal premotor (PMd), and posterior parietal (area5) cortices was performed in behaving monkeys trained in aninstructed-delay reaching task. The parietofrontal corticocorticatconnectivities of these same areas were subsequently examinedanatomically by means of retrograde tracing techniques. Signal-, set-, movement-, and position-related directional neuronalactivities were distributed nonuniformly within the task-relatedareas in both frontal and parietal cortices. Within the frontallobe, moving caudally from PMd to the MI, the activity thatsignals for the visuospatial events leading to target localizationdecreased, while the activity more directly linked to movementgeneration increased. Physiological recordings in the superior parietal lobule revealeda gradient-like distribution of functional properties similarto that observed in the frontal lobe. Signal- and set-relatedactivities were encountered more frequently in the intermediateand ventral part of the medial bank of the intraparietal sulcus(IPS), in area MIP. Movement- and position-related activitieswere distributed more uniformly within the superior parietallobule (SPL), in both dorsal area 5 and in MIP. Frontal and parietal regions sharing similar functional propertieswere preferentially connected through their association pathways.As a result of this study, area MIP, and possibly areas MDPand 7m as well, emerge as the parietal nodes by which visualinformation may be relayed to the frontal lobe arm region. Theseparietal and frontal areas, along with their association connections,represent a potential cortical network for visual reaching.The architecture of this network is ideal for coding reachingas the result of a combination between visual and somatic information.     

Cerebral bases of subliminal and supraliminal priming during reading

Several studies have investigated the neural correlates of conscious perception by contrasting functional magnetic resonance imaging (fMRI) activation to conscious and nonconscious visual stimuli. The results often reveal an amplification of posterior occipito-temporal activation and its extension into a parieto-frontal network. However, some of these effects might be due to a greater deployment of attentional or strategical processes in the conscious condition. Here, we examined the brain activity evoked by visible and invisible stimuli, both of which were irrelevant to the task. We collected fMRI data in a masking paradigm in which subliminal versus supraliminal letter strings were presented as primes while subjects focused attention on another subsequent, highly visible target word. Under those conditions, prime visibility was associated with greater activity confined to bilateral posterior occipito-temporal cortices, without extension into frontal and parietal cortices. However, supraliminal primes, compared with subliminal primes, evoked more extensive repetition suppression in a widely distributed set of parieto-frontal areas. Furthermore, only supraliminal primes caused phonological repetition enhancement in left inferior frontal and anterior insular cortex. Those results suggest a 2-stage view of conscious access: Relative to masked stimuli, unmasked stimuli elicit increased occipito-temporal activity, thus allowing them to compete for global conscious access and to induce priming in multiple distant areas. In the absence of attention, however, their access to a second stage of distributed parieto-frontal processing may remain blocked.     

Dissociating neural correlates of cognitive components in mental calculation

Mental calculation is a complex cognitive operation that is composed of a set of distinct functional processes. Using functional magnetic resonance imaging (fMRI), we mapped brain activity in healthy subjects performing arithmetical tasks and control tasks evoking a comparable load on visuo-constructive, linguistic, attentional and mnemonic functions. During calculation, as well as non-mathematical tasks, similar cortical networks consisting of bilateral prefrontal, premotor and parietal regions were activated, suggesting that most of these cortical areas do not exclusively represent modules for calculation but support more general cognitive operations that are instrumental but not specific to mental arithmetic. Significant differences between calculation and the non-mathematical tasks were found in parietal sub-regions, where non-arithmetic number or letter substitution tasks preferentially activated the superior parietal lobules whereas calculation predominantly elicited activation of the left dorsal angular gyrus and the medial parietal cortices. We interpret the latter activations to reflect sub-processes of mental calculation that are related to the processing of numerical representations during exact calculation and to arithmetical fact retrieval. Finally, we found that more complex calculation tasks involving the application of calculation rules increased activity in left inferior frontal areas that are known to subserve linguistic and working memory functions. Taken together, these findings help to embed the specific cognitive operation of calculation into a neural framework that provides the required set of instrumental components. This result may further inform the cognitive modeling of calculation and adds to the understanding of neuropsychological deficit patterns in patients.     

Attentional load and sensory competition in human vision: modulation of fMRI responses by load at fixation during task-irrelevant stimulation in the peripheral visual field

Perceptual suppression of distractors may depend on both endogenous and exogenous factors, such as attentional load of the current task and sensory competition among simultaneous stimuli, respectively. We used functional magnetic resonance imaging (fMRI) to compare these two types of attentional effects and examine how they may interact in the human brain. We varied the attentional load of a visual monitoring task performed on a rapid stream at central fixation without altering the central stimuli themselves, while measuring the impact on fMRI responses to task-irrelevant peripheral checkerboards presented either unilaterally or bilaterally. Activations in visual cortex for irrelevant peripheral stimulation decreased with increasing attentional load at fixation. This relative decrease was present even in V1, but became larger for successive visual areas through to V4. Decreases in activation for contralateral peripheral checkerboards due to higher central load were more pronounced within retinotopic cortex corresponding to 'inner' peripheral locations relatively near the central targets than for more eccentric 'outer' locations, demonstrating a predominant suppression of nearby surround rather than strict 'tunnel vision' during higher task load at central fixation. Contralateral activations for peripheral stimulation in one hemifield were reduced by competition with concurrent stimulation in the other hemifield only in inferior parietal cortex, not in retinotopic areas of occipital visual cortex. In addition, central attentional load interacted with competition due to bilateral versus unilateral peripheral stimuli specifically in posterior parietal and fusiform regions. These results reveal that task-dependent attentional load, and interhemifield stimulus-competition, can produce distinct influences on the neural responses to peripheral visual stimuli within the human visual system. These distinct mechanisms in selective visual processing may be integrated within posterior parietal areas, rather than earlier occipital cortex.     

Processing prosodic boundaries in natural and hummed speech: an FMRI study

Speech contains prosodic cues such as pauses between different phrases of a sentence. These intonational phrase boundaries (IPBs) elicit a specific component in event-related brain potential studies, the so-called closure positive shift. The aim of the present functional magnetic resonance imaging study is to identify the neural correlates of this prosody-related component in sentences containing segmental and prosodic information (natural speech) and hummed sentences only containing prosodic information. Sentences with 2 IPBs both in normal and hummed speech activated the middle superior temporal gyrus, the rolandic operculum, and the gyrus of Heschl more strongly than sentences with 1 IPB. The results from a region of interest analysis of auditory cortex and auditory association areas suggest that the posterior rolandic operculum, in particular, supports the processing of prosodic information. A comparison of natural speech and hummed sentences revealed a number of left-hemispheric areas within the temporal lobe as well as in the frontal and parietal lobe that were activated more strongly for natural speech than for hummed sentences. These areas constitute the neural network for the processing of natural speech. The finding that no area was activated more strongly for hummed sentences compared with natural speech suggests that prosody is an integrated part of natural speech.     

Metabolic alterations in the prefrontal and cingulate cortices are related to behavioral deficits in a rodent model of attention-deficit hyperactivity disorder

Rats with a deficit in selective attention accompanied by impulsivity can be identified using a five-choice serial reaction time task (5-CSRT) and have been proposed to represent a rodent model of attention-deficit hyperactivity disorder (ADHD). The aim of the present study was to investigate which brain areas are important for visuospatial attention and to test the specific hypothesis that dysfunction of the frontal cortex is related to the behavioral deficits observed in poorly performing rats. Therefore, [(14)C]deoxyglucose (DG) uptake, an index of brain metabolic activity, was measured during the performance of a 5-CSRT task in two populations of rats (poorly and well-performing rats) to study the relationships between the regional brain activity and behavioral output. While performing a 5-CSRT task, poorly performing rats exhibited lower DG uptake in the cingulate and ventrolateral orbital cortices than did well-performing rats,. Moreover, there was a positive correlation between choice accuracy and DG uptake in several areas, especially in the frontal and parietal regions, whereas there was an inverse correlation between the percentage of premature responses and DG uptake in the ventrolateral orbital and cingulate cortices.These results, which demonstrated that the poorly performing rats exhibited metabolic dysfunction in the cingulate and prefrontal cortices, provide a basis for the face validity of the rodent model of ADHD. Moreover, they suggest that the neural network of attention in rats is remarkably analogous to that described in primates.     

Impairment of gaze-centered updating of reach targets in bilateral parietal-occipital damaged patients

Recent studies have suggested that internal updating of visuospatial targets in humans occurs in gaze-centered coordinates and takes place in the parietal and extrastriate cortices. We explored how information for reaching is updated in two patients with bilateral lesions in these areas. Subjects performed two visuomotor tasks: (i) a fixation reaching task, which began with the appearance of one of five fixation positions (varying eye positions) followed by a central reaching target. Subjects reached to the target while fixating on the presented fixation position (relative to gaze the target was always presented in the periphery); and (ii) a saccade reaching task, in which subjects foveated on the central reaching target, then made a saccade to the presented fixation position before reaching to the central target. In both tasks, subjects reached to targets after a 500 or 5000 ms delay. Gaze-centered updating predicts similarities in reaching errors between fixation and saccade trials. Control subjects showed evidence for gaze-centered updating during both 500 and 5000 ms delay conditions. In contrast, patient AT, who had extensive occipital-parietal damage, only showed signs of gaze-centered representation after 5 s. Patient IG, with a more focal lesion in the parietal cortices, showed partial updating in gaze-centered coordinates when reaching with the small memory delay but recovered a complete gaze-centered representation after the longer delay. This suggests that patients with bilateral occipital-parietal lesions may rely on non-gaze-centered frames to store immediate target locations in reaching space but, given enough time, this information may be rerouted to access other gaze-centered motor cortical mechanisms.     

Multisensory interactions within human primary cortices revealed by BOLD dynamics

Whether signals from different sensory modalities converge and interact within primary cortices in humans is unresolved, despite emerging evidence in animals. This is partially because of debates concerning the appropriate analyses of functional magnetic resonance imaging (fMRI) data in response to multisensory phenomena. Using event-related fMRI, we observed that simple auditory stimuli (noise bursts) activated primary visual cortices and that simple visual stimuli (checkerboards) activated primary auditory cortices, indicative of multisensory convergence. Moreover, analyses of blood oxygen level-dependent response dynamics revealed facilitation of hemodynamic response peak latencies and slopes for multisensory auditory-visual stimuli versus either unisensory condition, indicative of multisensory interactions within primary sensory cortices. Neural processing at the lowest cortical levels can be modulated by interactions between the senses. Temporal information in fMRI data can reveal these modulations and overcome analytic and interpretational challenges of more traditional procedures. In addition to providing an essential translational link with animal models, these results suggest that longstanding notions of cortical organization need to be revised to include multisensory interactions as an inherent component of functional brain organization.     

The neural mechanisms underlying the Müller-Lyer illusion and its interaction with visuospatial judgments

Arrows terminating a line can distort the perceived line length. This so-called Müller-Lyer illusion can be used in healthy human subjects to mimic the performance of neglect patients in visuospatial judgments (e.g., in the landmark task). In this study, we investigated the neural mechanisms underlying the Müller-Lyer illusion, the landmark task, and their interaction. This was achieved by parametrically manipulating the magnitude of the Müller-Lyer illusion both in a landmark and in a luminance (control) task. As expected, the landmark task activated right posterior parietal cortex and right temporo-occipital cortex. In contrast, the neural processes associated with the strength of the Müller-Lyer illusion were located bilaterally in the lateral occipital cortex as well as the right superior parietal cortex. The data not only converge with but also extend neuropsychological data that indicate maintained line-length illusion in neglect patients. In addition, our results support the size-constancy scaling hypothesis as a putative mechanism underlying line-length illusions. Furthermore, activation that was driven by both the task and the strength of the Müller-Lyer illusion was observed in right intraparietal sulcus, thus arguing in favor of an interaction of illusory information with the top-down processes underlying visuospatial judgments in right parietal cortex.     

Brain activity during stimulation of the trigeminal nerve with noxious heat.

OBJECTIVE: The aim of this study was to observe areas of brain activation with painful hot stimulation to the trigeminal nerve. STUDY DESIGN: Nine healthy pain-free women (mean age 26.2 +/- 6.9 yrs) with a natural, regular menstrual cycle participated in the study. Whole-brain functional magnetic resonance imaging (fMRI) data were acquired for each participant on day 2 or 3 after the onset of menses using echo-planar imaging at 1.5T with near-isotropic spatial resolution and a temporal resolution of 4 s. RESULTS: Whole-brain fMRI with a Peltier thermode inside the head coil yielded a feasible imaging protocol with little disturbance from the thermode. Painful thermal stimulation of the left trigeminal system activated discrete brain regions within the insula, cingulate gyrus, thalamus, inferior parietal lobe/postcentral gyrus, right middle and inferior frontal gyri, cuneus, precuneus, and precentral gyrus. CONCLUSION: Painful stimulation of the trigeminal nerve resulted in activation of similar brain areas generally known for pain processing of painful peripheral stimulation.     

New Evidence for Distinct Right and Left Brain Systems for Deductive versus Probabilistic Reasoning.

Deductive and probabilistic reasoning are central to cognition but the functional neuroanatomy underlying them is poorly understood. The present study contrasted these two kinds of reasoning via positron emission tomography. Relying on changes in instruction and psychological 'set', deductive versus probabilistic reasoning was induced using identical stimuli. The stimuli were arguments in propositional calculus not readily solved via mental diagrams. Probabilistic reasoning activated mostly left brain areas whereas deductive activated mostly right. Deduction activated areas near right brain homologues of left language areas in middle temporal lobe, inferior frontal cortex and basal ganglia, as well as right amygdala, but not spatial-visual areas. Right hemisphere activations in the deduction task cannot be explained by spill-over from overtaxed, left language areas. Probabilistic reasoning was mostly associated with left hemispheric areas in inferior frontal, posterior cingulate, parahippocampal, medial temporal, and superior and medial prefrontal cortices. The foregoing regions are implicated in recalling and evaluating a range of world knowledge, operations required during probabilistic thought. The findings confirm that deduction and induction are distinct processes, consistent with psychological theories enforcing their partial separation. The results also suggest that, except for statement decoding, deduction is largely independent of language, and that some forms of logical thinking are non-diagrammatic.     

Contribution of working memory to transient activation in human inferior prefrontal cortex during performance of the Wisconsin Card Sorting Test.

The Wisconsin Card Sorting Test (WCST) is the standard task paradigm to detect human frontal lobe dysfunction. In this test, subjects sort card stimuli with respect to one of three possible dimensions (color, form and number). These dimensions are changed intermittently, whereupon subjects are required to identify by trial and error a new correct dimension and flexibly shift cognitive set. We decomposed the cognitive requirements at the time of the dimensional changes of the WCST, using functional magnetic resonance imaging (fMRI). By explicitly informing subjects of a new correct dimension, the working memory load for the trial-and-error identification of the new dimension was removed. Event-related fMRI still revealed transient activation time-locked to the dimensional changes in areas in the posterior part of the inferior frontal sulci. However, the activation was significantly smaller than in the original WCST in which subjects had to use working memory to identify the new dimension by trial and error. Furthermore, these areas were found to spatially overlap the areas activated by a working memory task. These results suggest that working memory and set-shifting act cooperatively in the same areas of prefrontal cortex to adapt us to changing environments.     

Language functional magnetic resonance imaging in preoperative assessment of language areas: correlation with direct cortical stimulation

OBJECTIVE: The aim of this study was to analyze the usefulness of preoperative language functional magnetic resonance imaging (fMRI), by correlating fMRI data with intraoperative cortical stimulation results for patients with brain tumors. METHODS: Naming and verb generation tasks were used, separately or in combination, for 14 right-handed patients with tumors in the left hemisphere. fMRI data obtained were analyzed with SPM software, with two standard analysis thresholds (P < 0.005 and then P < 0.05). The fMRI data were then registered in a frameless stereotactic neuronavigational device and correlated with direct brain mapping results. We used a statistical model with the fMRI information as a predictor, spatially correlating each intraoperatively mapped cortical site with fMRI data integrated in the neuronavigational system (site-by-site correlation). Eight patients were also studied with language fMRI postoperatively, with the same acquisition protocol. RESULTS: We observed high variability in signal extents and locations among patients with both tasks. The activated areas were located mainly in the left hemisphere in the middle and inferior frontal gyri (F2 and F3), the superior and middle temporal gyri (T1 and T2), and the supramarginal and angular gyri. A total of 426 cortical sites were tested for each task among the 14 patients. In frontal and temporoparietal areas, poor sensitivity of the fMRI technique was observed for the naming and verb generation tasks (22 and 36%, respectively) with P < 0.005 as the analysis threshold. Although not perfect, the specificity of the fMRI technique was good in all conditions (97% for the naming task and 98% for the verb generation task). Better correlation (sensitivity, 59%; specificity, 97%) was achieved by combining the two fMRI tasks. Variation of the analysis threshold to P < 0.05 increased the sensitivity to 66% while decreasing the specificity to 91%. Postoperative fMRI data (for the cortical brain areas studied intraoperatively) were in accordance with brain mapping results for six of eight patients. Complete agreement between pre- and postoperative fMRI studies and direct brain mapping results was observed for only three of eight patients. CONCLUSION: With the paradigms and analysis thresholds used in this study, language fMRI data obtained with naming or verb generation tasks, before and after surgery, were imperfectly correlated with intraoperative brain mapping results. A better correlation could be obtained by combining the fMRI tasks. The overall results of this study demonstrated that language fMRI could not be used to make critical surgical decisions in the absence of direct brain mapping. Other acquisition protocols are required for evaluation of the potential role of language fMRI in the accurate detection of essential cortical language areas.     

Functional MRI of the human brain responses to olfactory stimulation

Image artifacts such as signal loss or distortion due to intravoxel phase dispersion at the skull base are problematic in analysis by functional MRI (fMRI). Since the olfactory center of the brain is located in the medial temporal and basal frontal areas, it is a challenge to try to detect the Blood Oxygenation Level Dependent (BOLD) effect during fMRI at olfactory stimulation. We examined 20 normal volunteers with a 1.5-T MR system, employing multishot, interleaved echo-planar imaging (EPI). Olfactory stimulation was performed with 2-methyl-1, 3-cyclo-pentanedione, a caramel-like fragrance, by presenting it for 20 seconds with two cycles of rest-stimulus paradigm. Sites of functional activation were identified by correlation analysis with a threshold of p < 0.01. Most commonly activated areas were the orbitofrontal and primary olfactory cortices. Mild activation was also observed in the cingulate gyrus, lateral temporal cortex, cerebellum, parietal and occipital lobes. These results indicate that olfactory stimulation participates in the emotion and behavior processes. Interestingly, broad activation in the "silent" area of the frontal and temporal lobe was also observed in some cases. Multishot EPI was a useful method to evaluate brain activation at the basal level on fMRI.     

Brain activity related to working memory and distraction in children and adults

In order to retain information in working memory (WM) during a delay, distracting stimuli must be ignored. This important ability improves during childhood, but the neural basis for this development is not known. We measured brain activity with functional magnetic resonance imaging in adults and 13-year-old children. Data were analyzed with an event-related design to isolate activity during cue, delay, distraction, and response selection. Adults were more accurate and less distractible than children. Activity in the middle frontal gyrus and intraparietal cortex was stronger in adults than in children during the delay, when information was maintained in WM. Distraction during the delay evoked activation in parietal and occipital cortices in both adults and children. However, distraction activated frontal cortex only in children. The larger frontal activation in response to distracters presented during the delay may explain why children are more susceptible to interfering stimuli.