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Results for “Dorsolateral Prefrontal Cortex”

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PubMed2006

A randomized, sham-controlled, proof of principle study of transcranial direct current stimulation for the treatment of pain in fibromyalgia.

OBJECTIVE: Recent evidence suggests that fibromyalgia is a disorder characterized by dysfunctional brain activity. Because transcranial direct current stimulation (tDCS) can modulate brain activity noninvasively and can decrease pain in patients with refractory central pain, we hypothesized that tDCS treatment would result in pain relief in patients with fibromyalgia. METHODS: Thirty-two patients were randomized to receive sham stimulation or real tDCS with the anode centered over the primary motor cortex (M1) or the dorsolateral prefrontal cortex (DLPFC) (2 mA for 20 minutes on 5 consecutive days). A blinded evaluator rated the patient's pain, using the visual analog scale for pain, the clinician's global impression, the patient's global assessment, and the number of tender points. Other symptoms of fibromyalgia were evaluated using the Fibromyalgia Impact Questionnaire and the Short Form 36 Health Survey. Safety was assessed with a battery of neuropsychological tests. To assess potential confounders, we measured mood and anxiety changes throughout the trial. RESULTS: Anodal tDCS of the primary motor cortex induced significantly greater pain improvement compared with sham stimulation and stimulation of the DLPFC (P < 0.0001). Although this effect decreased after treatment ended, it was still significant after 3 weeks of followup (P = 0.004). A small positive impact on quality of life was observed among patients who received anodal M1 stimulation. This treatment was associated with a few mild adverse events, but the frequency of these events in the active-treatment groups was similar to that in the sham group. Cognitive changes were similar in all 3 treatment groups. CONCLUSION: Our findings provide initial evidence of a beneficial effect of tDCS in fibromyalgia, thus encouraging further trials.

Chronic Disease↗

PubMed2004

Decreased activation of the anterior cingulate in bipolar patients: an fMRI study.

BACKGROUND: Previous neuroimaging investigations of patients with bipolar disorder have reported abnormalities of the frontal subcortical network. The role of the anterior cingulate cortex (ACC) and the dorsolateral prefrontal cortex (DLPFC) in bipolar disorder are not clear, although both regions have been shown to be components of a neural network which plays a critical role in the completion of tasks requiring self-monitoring and inhibition, functions often noted to be altered in bipolar patients. fMRI studies have helped clarify the role of specific subdivisions of the ACC and the DLPFC during the performance of cognitive challenges, including the Stroop color word test. To date, studies that have examined ACC function in bipolar patients have not differentiated subregions within this area, nor have they examined changes in these subregions in relation with DLPFC activation. METHODS: To help clarify the specific roles of these regions in bipolar patients, we examined stable patients and control subjects during performance of the Stroop test using BOLD fMRI techniques. We hypothesized that bipolar patients would demonstrate reduced activation of two subdivisions of the ACC (AAA and VOA), as well as altered activation of the DLPFC, during the interference condition. RESULTS: Results indicate that relative to controls, bipolar patients demonstrated significantly reduced signal intensity within the right AAA subdivision (p=0.011), which accompanied an increase in the DLPFC (p=0.049) during the task. LIMITATIONS: The study sample was somewhat small (11 patients, 10 controls) which limits the generalizability of the study findings, however, the patient sample consisted of well-diagnosed, stable, chronic individuals with bipolar disorder and the sample size provided enough power to detect between-group differences. CONCLUSIONS: These findings suggest differential processing strategies of bipolar patients and support the theory of altered frontal systems in these patients during the performance of cognitive tasks.

Adult↗

PubMed2001

The motion aftereffect: more than area V5/MT? Evidence from 15O-butanol PET studies.

The motion aftereffect is a perceptual phenomenon which has been extensively investigated both psychologically and physiologically. Neuroimaging techniques have recently demonstrated that area V5/MT is activated during the perception of this illusion. The aim of this study was to test the hypothesis if a more broadly distributed network of brain regions subserves the motion aftereffect. To identify the neuronal structures involved in the perception of the motion aftereffect, regional cerebral blood flow (rCBF) measurements with positron emission tomography were performed in six normal volunteers. Data were analysed using SPM96. The motion-sensitive visual areas including area V5/MT were activated in both hemispheres. Additionally, the lateral parietal cortex bilaterally, the right dorsolateral prefrontal cortex, the anterior cingulate cortex and the left cerebellum showed significant increases in rCBF values during the experience of the waterfall illusion. In a further reference condition with identical attentional demand but no perception of a motion aftereffect elevated rCBF were found in these regions as well. In conclusion, our findings support the notion that the perceptual illusion of motion arises exclusively in the motion-sensitive visual area V5/MT. In addition, a more widespread network of brain regions including the prefrontal and parietal cortex is activated during the waterfall illusion which represents a non-motion aftereffect-specific subset of brain areas but is involved in more basic attentional processing and cognition.

Adult↗

PubMed2003

Switching attention and resolving interference: fMRI measures of executive functions.

Is there a single executive process or are there multiple executive processes that work together towards the same goal in some task? In these experiments, we use counter switching and response inhibition tasks to examine the neural underpinnings of two cognitive processes that have often been identified as potential executive processes: the switching of attention between tasks, and the resolution of interference between competing task responses. Using functional magnetic resonance imaging (fMRI), for both event-related and blocked design tasks, we find evidence for common neural areas across both tasks in bilateral parietal cortex (BA 40), left dorsolateral prefrontal cortex (DLPFC; BA 9), premotor cortex (BA 6) and medial frontal cortex (BA 6/32). However, we also find areas preferentially involved in the switching of attention between mental counts (BA 7, BA 18) and the inhibition of a prepotent motor response (BA 6, BA 10), respectively. These findings provide evidence for the separability of cognitive processes underlying executive control.

Adolescent↗

PubMed2001

Visual activation of frontal cortex: segregation from occipital activity.

Studies in primates have found visually responsive neurons that are distributed beyond cortical areas typically described as directly involved in vision. Among these areas are premotor cortex, supplementary motor area, dorsolateral prefrontal cortex and frontal eye fields. Given these findings, visual stimulation would be expected to result in activation of human frontal cortex. However, few human studies have described sensory activations in frontal regions in response to simple visual stimulation. Such studies have classically described event-related potential (ERP) components over occipital regions. The present study sought to further characterize the spatiotemporal dynamics of visually-evoked electrocortical responses elicited by simple visual stimuli using scalp current density measures derived from high-density ERP recordings, with particular emphasis on the distribution of stimulus-related activity over frontal cortex. Hemiretinal stimuli were viewed passively and during a simple ipsi- or contramanual (RT) task. The motor requirement was included to investigate the effects of response preparation on premovement frontal activations. The results indicate early frontocentral activation, particularly over the right hemisphere (peak magnitude 124-148 ms) that is independent of input visual field or motor response requirement, and that is clearly separate in timecourse from the posterior responses elicited by visual input. These findings are in accord with the multiplicity of visual inputs to frontal cortex and are discussed in terms of frontal lobe functions as may be required in these tasks.

Adult↗

PubMed2002

Functional magnetic resonance imaging of brain activity in the visual oddball task.

Abnormalities in the P300 ERP, elicited by the oddball task and measured using EEG, have been found in a number of central nervous system disorders including schizophrenia, Alzheimer's disease, and alcohol dependence. While electrophysiological studies provide high temporal resolution, localizing the P300 deficit has been particularly difficult because the measurements are collected from the scalp. Knowing which brain regions are involved in this process would elucidate the behavioral correlates of P300. The aim of this study was to determine the brain regions involved in a visual oddball task using fMRI. In this study, functional and high-resolution anatomical MR images were collected from seven normal volunteers. The data were analyzed using a randomization-based statistical method that accounts for multiple comparisons, requires no assumptions about the noise structure of the data, and does not require spatial or temporal smoothing. Activations were detected (P<0.01) bilaterally in the supramarginal gyrus (SMG; BA 40), superior parietal lobule (BA 7), the posterior cingulate gyrus, thalamus, inferior occipitotemporal cortex (BA 19/37), insula, dorsolateral prefrontal cortex (BA 9), anterior cingulate cortex (ACC), medial frontal gyrus (BA 6), premotor area, and cuneus (BA 17). Our results are consistent with previous studies that have observed activation in ACC and SMG. Activation of thalamus, insula, and the occipitotemporal cortex has been reported less consistently. The present study lends further support to the involvement of these structures in visual target detection.

Adult↗

PubMed2003

Are action and perception in near and far space additive or interactive factors?

Functional imaging has revealed differential neural mechanisms underlying action directed toward near or far space. Because some neuropsychological studies of patients with visuospatial neglect failed to show near/far dissociations with perceptual tasks, we investigated whether action and perception elicit distinct cerebral representations in near and far space. We measured regional cerebral blood flow with positron emission tomography in normal volunteers who performed manual line bisection (action) and made line bisection judgments (perception). Stimuli were presented in near space or far space. Far space presentation enhanced activations in occipital cortex extending into the medial occipitotemporal cortex bilaterally, while near space presentation enhanced left occipital-parietal, parietal, and premotor cortex activity. Manual bisection activated the extrastriate, superior parietal, and premotor cortex bilaterally, while bisection judgments activated the right inferior parietal cortex, anterior cingulate, right dorsolateral prefrontal cortex, and extrastriate and superior temporal cortex bilaterally. The neural mechanisms responsible for the two tasks (perceptual/motor) were not differentially modulated by space of presentation.

Adult↗

PubMed1999

Repetitive transcranial magnetic stimulation: perspectives for application in the treatment of bipolar and unipolar disorders.

OBJECTIVES: Transcranial magnetic stimulation (TMS) affects the brain by non-invasively stimulating the cerebral cortex and inducing electrical currents in neurons. The powerful magnetic field acts as a vector that passes across the scalp and the skull, and then converts into an electrical energy within the brain. Originally used in neurophysiology, TMS has since been applied in a variety of neuropsychiatric conditions, including mood disorders. Imaging studies in mood-disordered patients have pointed to dysfunctional limbic and prefrontal cortex activity. TMS researchers have thus postulated that dorsolateral prefrontal cortex (DLPFC) stimulation might change brain activity both locally and in paralimbic areas through transynaptic connections, and alter mood. METHODS: We will describe the technology of TMS, its applications to date, and explore its mechanisms of action. RESULTS: Several clinical trials have demonstrated TMS effects on mood in health and disease. There is a growing consensus that TMS has antidepressant effects, although little is known about the role played by a variety of stimulation parameters such as the intensity or frequency of stimulation. One study has found an antimanic effect of right prefrontal TMS. CONCLUSION: TMS is relatively safe; however, much more research is needed before TMS can be integrated into routine clinical practice.

Bipolar Disorder↗

PubMed2002

Effect of attention on central auditory processing: an fMRI study.

Functional magnetic resonance imaging was used to investigate preattentive and attentional processing of auditory stimuli in 18 right-handed normal volunteers. Responses to trains of 1000-Hz pure tones and infrequent (15%) deviant 1300-Hz tones were characterized while subjects ignored all tones; listened for deviants in the left ear; or listened for deviants in the right ear. Preattentive detection of deviants, associated with the mismatch negativity in electrophysiology, was associated with bilateral temporal lobe activation, with a rightward predominance. Processing of deviant stimuli while attending to either ear produced a more robust and widespread activation of these temporal regions, again with a rightward predominance. Thus, preattentive tone processing appears to be linked to asymmetric activation of a core set of temporal regions in which activity is significantly amplified by selective attention. Extratemporal regions activated by attending to targets in either ear included the anterior cingulate cortex, supramarginal gyrus, and dorsolateral prefrontal cortex.

Acoustic Stimulation↗

PubMed1991

Cortical control of reflexive visually-guided saccades.

Reflexive visually-guided saccade triggering may be facilitated or inhibited by the cerebral cortex. To study this control, saccades made towards suddenly appearing visual targets (saccade task) or away from them (antisaccade task) were recorded electro-oculographically in 45 patients with limited unilateral cerebral infarction. Lesions affected (1) the superior part of the angular gyrus (area 39 of Brodmann) in the posterior parietal cortex (PPC), (2) the dorsolateral prefrontal cortex (PFC) (area 46 of Brodmann), (3) the frontal eye field (FEF), or (4) the supplementary motor area (SMA). As these 4 types of lesions were located either in the right or the left cerebral hemisphere, patients were divided into 8 groups. Saccade latency, in the saccade task, and the percentage of errors (misdirected saccades made towards the visual target), in the antisaccade task, were compared in each group of patients with the values of 20 control subjects. In the saccade task, saccade latency was significantly increased bilaterally in the right PPC group. In the left PPC group, the increase in latency was less marked, and significant only for saccades made contralaterally to the lesion. In the different frontal groups, latency was unchanged or only slightly increased. These results confirm that the main area facilitating the triggering of reflexive visually-guided saccades is located in the PPC, in or near the superior part of the angular gyrus. The difference between right and left parietal lesions could be due to the predominance of the right hemisphere in the control of these saccades. In the antisaccade task, the percentage of errors was significantly increased bilaterally in both PFC groups compared with the control group and also to the FEF and SMA groups. These results suggest that the PFC is the main area in the cerebral hemisphere inhibiting reflexive visually-guided saccades.

Cerebral Cortex↗

PubMed1999

The effects of learning and intention on the neural network involved in the perception of meaningless actions.

PET was used to explore the neural network involved in the perception of meaningless action. In two conditions, subjects observed learned and unknown meaningless actions without any purpose. In two other conditions, subjects observed the same type of stimuli for later imitation. The control condition, which consisted of the presention of stationary hands, served as a baseline. Unsurprisingly, a common network that forms part of the dorsal pathway was engaged in all conditions when compared with stationary hands, and this was interpreted as being devoted to the analysis of hand movements. One of the most striking results of the present study was that some brain areas were strongly modulated by the learning level, independent of the subject's intention. Two different effects were observed: a reduced activity in posterior regions within the common network, which correlated with specific increases in the frontopolar area 10 and in the angular gyrus during the perception of learned meaningless actions compared with the perception of unknown actions. Finally, the major effect of the subject's intention to imitate was a strong increase in the dorsal pathway extending to the lateral premotor cortex and to the dorsolateral prefrontal cortex, which reflects the information processing needed for prospective action. Overall, our results provide evidence for both an effect of the visuomotor learning level and of the subject's intention on the neural network involved during the perception of human meaningless actions.

Adult↗

PubMed2006

Distinct neural correlates for resolving stroop conflict at inhibited and noninhibited locations in inhibition of return.

It is well documented that the anterior cingulate cortex (ACC) and the dorsolateral prefrontal cortex (DLPFC) are intensively involved in conflict control. However, it remains unclear how these "executive" brain regions will act when the conflict control process interacts with spatial attentional orienting. In the classical spatial cueing paradigm [Posner, M. I., & Cohen, Y. (1984). Components of visual orienting. In H. Bouma & D. G. Bouwhuis (Eds.), Attention and performance X (pp. 531-556). Hillsdale, NJ: Erlbaum], response to a target is delayed when it appears at the cued location compared with at the uncued location, if the time interval between the cue and the target is greater than 300 msec. This effect of inhibition of return (IOR) can alter the resolution of Stroop conflict such that the Stroop interference effect disappears at the cued (inhibited) location [Vivas, A. B., & Fuentes, L. J. Stroop interference is affected in inhibition of return. Psychonomic Bulletin and Review, 8, 315-323, 2001]. In this event-related functional magnetic resonance study, we investigate the differential neural mechanisms underlying interactions between pre-response interference, response interference, and spatial orienting. Two types of Stroop words [incongruent response-eligible words (IE), incongruent response-ineligible words (II)] and neutral words were presented either at the cued or uncued location. The significant pre-response interference at the uncued location activated the left rostral ACC as compared with at the cued location. Moreover, although the IE words which have conflicts at both pre-response and response levels did not cause significant behavioral interference at the cued location, they activated the left DLPFC as compared with at the uncued location. Furthermore, neutral words showed significant IOR effects behaviorally, and they activated the left frontal eye field (FEF) at the uncued location relative to the cued location. These results suggest that the left rostral ACC is involved in the interaction between pre-response conflict and IOR, whereas the left DLPFC is involved in the interaction between response conflict and IOR. Moreover, the FEF is involved in shifting attentional focus to novel locations during spatial search.

Adult↗

PubMed2004

Integrating rewards and cognition in the frontal cortex.

Research indicates that the dorsolateral prefrontal cortex (DLPFC) contributes to working memory and executive control, whereas the ventral frontal cortex (VFC) contributes to affective and motivational processing. Few studies have examined both the functional specificity and the integration of these regions. We did so using fMRI and a verbal working memory task in which visual cues indicated whether recall performance on an upcoming trial would be linked to a monetary reward. On the basis of prior findings obtained in delayed response tasks performed by nonhuman primates, we hypothesized that (1) VFC would show an increase only in response to a cue indicating potential for a monetary reward; (2) DLPFC would show sustained activity across a delay interval for all trials, though activity in rewarded trials would be enhanced; and (3) regions engaged in speech-based rehearsal would be relatively insensitive to monetary incentive. Our hypotheses about DLPFC and rehearsal-related regions were confirmed. In VFC regions, we failed to observe statistically significant effects of reward when the cue or delay epochs of the task were examined in isolation. However, an unexpected and significant deactivation was observed in VFC during the delay epoch; furthermore, a post hoc voxelwise analysis indicated a complex interaction between (1) the cue and delay epochs of the task and (2) the reward value of the trials. The pattern of activation and deactivation across trial types suggests that VFC is sensitive to reward cues, and that portions of DLPFC and VFC may work in opposition during the delay epoch of a working memory task in order to facilitate task performance.

Adolescent↗

PubMed2000

Phonological and semantic fluencies are mediated by different regions of the prefrontal cortex.

Verbal phonological and semantic fluencies were investigated in 24 patients with unilateral prefrontal lesions and 10 normal control subjects. Lesions were limited to small areas within either the dorsolateral (Brodmann's area 46/9) or ventromedial (posterior part of the gyrus rectus) cortices. In a phonological fluency task, patients with lesions to the left dorsolateral region were impaired. In semantic fluency, not only the left dorsolateral group but also the two right frontal damaged groups performed worse than the control group. In agreement with previous studies, our results show that the phonological fluency is mediated by the left dorsolateral prefrontal cortex. In contrast to this, performance on the semantic fluency task depends on a wider portion of the prefrontal cortex involving the left and right dorsolateral and the right ventromedial areas.

Adult↗

PubMed2001

The sensory nature of mnemonic representation in the primate prefrontal cortex.

A long-standing issue concerning the function of the primate dorsolateral prefrontal cortex is whether the activity of prefrontal neurons reflects the perceived sensory attributes of a remembered stimulus, or the decision to execute a motor response. To distinguish between these possibilities, we recorded neuronal activity from monkeys trained to make a saccade toward the brighter of two memoranda, under conditions of varied luminance. Our results indicated that during the delay period when sensory information was no longer available, neuronal discharge was modulated by the luminance of the stimulus appearing in the receptive field, and was directly correlated with psychophysical performance in the task. The findings suggest that although prefrontal cortex codes for a diversity of representations, including the decision for an impending response, a population of neurons maintains the dimensional attributes of remembered stimuli throughout the delay period, which allows for flexibility in the outcome of a mnemonic process.

Action Potentials↗

PubMed2004

[Disorders of executive consciousness].

UNLABELLED: Executive function is a higher order cognitive capacity that involves memory, perception and performance of complex tasks. Disorders of the executive functions are sign of lesions in the prefrontal cortex, involving the prefrontal-striatal-thalamic networks and the parietal association areas. According to signs and localization, five basic prefrontal syndromes are recognised. 1. Damage in posterior dorsolateral prefrontal cortex and subcortical nuclei causes the dorsolateral syndrome with impaired decision making, working memory and planning. 2. The ventromedial-orbitofrontal syndrome: if lesion spares the basal forebrain, memory can be preserved, but poor social decision making develops. 3. The dorsomedial syndrome consists of attention disorder, akinesia, mutism and apathy. 4. The bilateral ventrolateral prefrontal regions serve perception of self and environment. 5. The ventral lateral (verbalizer) area of the dominant hemisphere coordinates language. Executive impairments can be found in cerebrovascular, Parkinson's and other diseases of basal ganglia, and in frontotemporal lobar degeneration. The dorsolateral syndrome can be examined by the use of Wisconsin card sorting test, self ordered pointing task and the delayed response task. Prefrontal-basal function can be assessed by Gambling-, Faux Pas-, and Emotion identification tasks. CONCLUSIONS: 1. A dysexecutive syndrome does not fulfil the criteria of dementia. 2. A "frontal syndrome" is an indefinite eponym. Focal lesions in prefrontal systems lead to localization-specific symptoms, which can be defined by psychometric tests. 3. In neurological diseases associated with multifocal damage of the brain neuropsychologic tests may help to determine strategic lesions, which are responsible for the actual syndromes.

Akinetic Mutism↗

PubMed2001

Selective deficits in prefrontal cortex function in medication-naive patients with schizophrenia.

BACKGROUND: Previously we proposed that dorsolateral prefrontal cortex (PFC) supports a specific working memory (WM) subcomponent: the ability to represent and maintain context information necessary to guide appropriate task behavior. By context, we mean prior task-relevant information represented in such a form that it supports selection of the appropriate behavioral response. Furthermore, we hypothesized that WM deficits in schizophrenia reflect impaired context processing due to a disturbance in dorsolateral PFC. We use functional magnetic resonance imaging to examine PFC activation in medication-naive, first-episode patients with schizophrenia during a WM, task-isolating context processing. METHODS: Fourteen first-episode, medication-naive patients with schizophrenia and 12 controls similar in age, sex, and parental education underwent functional magnetic resonance imaging during performance of an A-X version of the Continuous Performance Test. RESULTS: Patients with schizophrenia demonstrated deficits in dorsolateral PFC activation in task conditions requiring context processing but showed intact activation of posterior and inferior PFC. In addition, patients demonstrated intact activation of the primary motor and somatosensory cortex in response to stimulus processing demands. CONCLUSIONS: These results demonstrate selectivity in dorsolateral PFC dysfunction among medication-naive first-episode patients with schizophrenia, suggesting that a specific deficit in PFC function is present at illness onset, prior to the administration of medication or the most confounding effects of illness duration. Furthermore, these results are consistent with the hypothesis that WM deficits in patients with schizophrenia reflect an impairment in context processing due to a disturbance in dorsolateral PFC function.

Adult↗

PubMed2000

The prefrontal cortex: response selection or maintenance within working memory?

It is controversial whether the dorsolateral prefrontal cortex is involved in the maintenance of items in working memory or in the selection of responses. We used event-related functional magnetic resonance imaging to study the performance of a spatial working memory task by humans. We distinguished the maintenance of spatial items from the selection of an item from memory to guide a response. Selection, but not maintenance, was associated with activation of prefrontal area 46 of the dorsal lateral prefrontal cortex. In contrast, maintenance was associated with activation of prefrontal area 8 and the intraparietal cortex. The results support a role for the dorsal prefrontal cortex in the selection of representations. This accounts for the fact that this area is activated both when subjects select between items on working memory tasks and when they freely select between movements on tasks of willed action.

Animals↗