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Results for “Dorsolateral Prefrontal Cortex”

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PubMed1996

Cerebral activation during the exertion of sustained static force in man.

The aim of our study was to determine alterations of cerebral activity during prolonged static force exertion. Regional cerebral blood flow (rCBF) was measured using H2(15)O positron emission tomography (PET) while six male normal subjects pressed a morse-key with their right index finger with a constant force of 20% of their maximal voluntary contraction (MVC) for different periods of time (1.5-4.5 min). Exertion of static force led to activation which was at least as extensive as that during exertion of repetitive dynamic force pulses. Despite a considerable sense of fatigue and increased effort at the end of a 4.5 min key press, no compensatory changes of activity were detected in motor or sensory related structures. The right dorsolateral prefrontal cortex demonstrated a significant correlation between rCBF and duration of key-press, possibly reflecting processes over-riding fatigue. Prominent basal ganglia activation was demonstrated in this static force task, but not in a previous force task involving repetitive dynamic force pulses. This suggests that sustained exertion of a static force is an active process modulated, at least in part, by the basal ganglia.

Adult↗

PubMed1997

Mental navigation along memorized routes activates the hippocampus, precuneus, and insula.

Positron emission tomography was used to investigate the functional anatomy of mental simulation of routes (MSR) in five normal volunteers. Normalized regional cerebral blood flow was measured while subjects mentally navigated between landmarks of a route which had been previously learned by actual navigation. This task was contrasted with both static visual imagery of landmarks (VIL) and silent Rest. MSR appears to be subserved by two distinct networks: a non-specific memory network including the posterior and middle parts of the hippocampal regions, the dorsolateral prefrontal cortex and the posterior cingulum, and a specific mental navigation network, comprising the left precuneus, insula and medial part of the hippocampal regions.

Adult↗

PubMed1997

A functional magnetic resonance imaging study of episodic memory.

We have used whole brain fMRI and canonical variate analysis to investigate the anatomical location of brain activity subserving episodic memory encoding and recognition. Recognition of previously presented words did not specifically activate right prefrontal areas although right-sided activations were seen during transitions between the target and reference phases of the paradigm. Encoding was associated with left sided prefrontal activation, but this was within Broca's area rather than dorsolateral prefrontal cortex. The temporal resolution of fMRI, combined with analysis of the apparent functional connectivity of activations observed, revealed activity within complex networks each functionally specialized for the demands of particular aspects of a cognitive task.

Adult↗

PubMed1999

Electrophysiological evidence of two different types of error in the Wisconsin Card Sorting Test.

The specificity of the Wisconsin Card Sorting Test (WCST) for assessing frontal lobe pathology remains controversial, although lesion and cerebral blood flow studies continue to suggest a role for the dorsolateral prefrontal cortex in WCST performance. Inconsistencies might derive from the extended use of various WCST scores as equivalent indicators of frontal pathology. In this study, event-related potentials (ERPs) were recorded from 32 normal subjects who committed perseverative and non-perseverative errors. Both types of WCST errors evoked anomalous but distinct ERP patterns over frontal lobe regions. Perseverative errors were also associated with a dysfunctional extrastriate response to stimulation. This evidence suggests that perseverative and non-perseverative errors result from disruptions in two different prefrontal neural networks engaged during card sorting.

Adult↗

PubMed2001

An fMRI study of stimulus equivalence.

In order to study brain activation during the formation of equivalence relations, 12 subjects underwent fMRI during matching-to-sample (MTS) tests of (1) previously trained arbitrary relationships between iconic stimuli and the untrained, emergent relations of (2) symmetry, (3) transitivity, and (4) symmetry with transitivity, plus a test of verbal fluency (VF). Brain activation was similar in all MTS tasks and in the VF task. In particular, both types of task activated dorsolateral prefrontal cortex (DLPFC) and posterior parietal cortex bilaterally. However VF, but not the MTS tasks, activated Broca's area. In three of the four MTS tasks, behavioural accuracy was significantly correlated with left lateralisation of DLPFC activity. Brain activation patterns during equivalence thus resembled those involved in semantic processing underlying language, without involving regions concerned with the simple sub-vocal articulation of stimulus names.

Adult↗

PubMed2001

An fMRI study of anticipation and learning of smooth pursuit eye movements in humans.

We studied the neural substrate of anticipation and learning of smooth pursuit eye movements in humans using fMRI. Both predictable and non-predictable eye movements, compared to baseline, activated a common network previously associated with oculomotor function. The temporal dynamics of activity in a subset of these areas suggested a strong correlation with type of condition. Specifically, differential decreases in activity were seen in dorsolateral prefrontal cortex and the intraparietal sulcus during the predictable condition. During the non-predictable condition the same areas exhibited evidence of high levels of activity that further increased throughout the condition. In contrast, differential increases associated with the predictable condition were seen in anterior cingulate and preSMA cortex regions. These changes in activity mirror the time course of the short-term learning of eye movements seen behaviourally, and are congruent with learning-related changes that have been reported for other motor paradigms.

Adult↗

PubMed2001

Timing and magnitude of frontal activity differentiates refixation and anti-saccade performance.

EEG data were recorded while 10 subjects generated refixation saccades towards a visual target and antisaccades away from a visual cue. Theoretically, the same basic neural circuitry supports refixation and correct anti-saccade performances, with additional activity in primarily dorsolateral prefrontal cortex circuitry supporting antisaccade-associated inhibitory processes. Analyses demonstrated that sensory registration of visual stimuli is similar for refixation and anti-saccade conditions. Increased frontal brain activity at 5 and 15 Hz was observed preceding correct antisaccades when compared to refixation saccades. These analyses provide specific information suggesting that 160-60 ms before saccade generation is the critical period for response inhibition.

Adult↗

PubMed2001

Making sense during conversation: an fMRI study.

Although language is thought of as a left hemisphere function, there is increasing evidence that the right hemisphere contributes to language processing by identifying the theme of spoken and written language. Using fMRI, we examined the role played by the right and left hemispheres in making sense of a conversation. When this process involves implicit appraisal of changes in the conversation's topic, the neural network has a right hemisphere bias and includes Broca's and Wernicke's areas, their right hemisphere homologues, right dorsolateral prefrontal cortex, and the cerebellum. When making sense of conversation involves appraisal of the conversation's reasoning, however, the network includes Broca's and Wernicke's areas. Thus, right and left hemisphere systems contribute uniquely to the linguistic skills involved in making sense of a conversation.

Adult↗

PubMed2002

A neural network elicited by parametric manipulation of the attention load.

We used a parametric experimental design to identify the rCBF variations related to a continuous variation of the attention load. The experiment involved goal-directed visual tasks. The length of time during which the subject's attention was engaged toward the external stimulus was taken as the factor of interest. The neural network revealed areas that positively (left cerebellum, bilateral MT/V5 complex and superior parietal lobule, right inferior temporal lobe and dorsolateral prefrontal cortex) or negatively (precuneus, anterior cingulate and medial superior frontal cortex) correlate with the attention load. Results demonstrate that the activity of these areas varies continuously as a function of the variation in the attention load.

Adult↗

PubMed2005

Functional magnetic resonance imaging measure of automatic and controlled auditory processing.

Activity within fronto-striato-temporal regions during processing of unattended auditory deviant tones and an auditory target detection task was investigated using event-related functional magnetic resonance imaging. Activation within the middle frontal gyrus, inferior frontal gyrus, anterior cingulate gyrus, superior temporal gyrus, thalamus, and basal ganglia were analyzed for differences in activity patterns between the two stimulus conditions. Unattended deviant tones elicited robust activation in the superior temporal gyrus; by contrast, attended tones evoked stronger superior temporal gyrus activation and greater frontal and striatal activation. The results suggest that attention enhances neural activation evoked by auditory pitch deviance in auditory brain regions, possibly through top-down control from the dorsolateral prefrontal cortex involved in goal-directed selection and response generation.

Acoustic Stimulation↗

PubMed2005

Left prefrontal repetitive transcranial magnetic stimulation impairs performance in affective go/no-go task.

Functional neuroimaging studies have associated affective go/no-go function with lateral prefrontal activation, but they have not established a causal role and have not determined whether one hemisphere is predominantly engaged. In the present study, 11 normal volunteers underwent slow repetitive transcranial magnetic stimulation of the left and right dorsolateral prefrontal cortex, and the occipital cortex prior to performance of a picture-based affective go/no-go task. We found an interfering effect of left prefrontal repetitive transcranial magnetic stimulation compared with both right prefrontal and occipital repetitive transcranial magnetic stimulation. This impairment concerned positive and negative task stimuli to a similar extent, and tended to be greater in shift compared with nonshift blocks. Our findings demonstrate a functionally relevant lateralization of the prefrontal contribution to affective go/no-go tasks.

Adult↗

PubMed2003

Relative effects of repetitive transcranial magnetic stimulation and electroconvulsive therapy on mood and memory: a neurocognitive risk-benefit analysis.

OBJECTIVE: Two procedures for treating major depressive disorder were compared with regard to their respective effects on mood and cognition. BACKGROUND: Fourteen patients underwent treatment with electroconvulsive therapy and 14 underwent treatment with repetitive transcranial magnetic stimulation. Patients were tested on three occasions: before initiation of treatment, at the end of treatment, and 2 weeks after the end of treatment. METHODS: Electroconvulsive therapy was applied unilaterally approximately three times per week for 2 to 4 weeks. Repetitive transcranial magnetic stimulation was applied in sessions of 1600 stimuli at 10 Hertz and 90% of motor threshold intensity to the left dorsolateral prefrontal cortex daily (Monday through Friday) for 2 consecutive weeks. RESULTS: Results indicate that electroconvulsive therapy had a more positive effect on mood than did a 2-week trial of repetitive transcranial magnetic stimulation. With regard to cognitive outcome measures, electroconvulsive therapy exerted a deleterious but transient effect on various components of memory that were no longer detected 2 weeks after the end of treatment; however, there was evidence of persistent retrograde amnesia after treatment with electroconvulsive therapy. As a group, repetitive transcranial magnetic stimulation patients experienced only a modest reduction in depression severity but there was no evidence of anterograde or retrograde memory deficits in the aftermath of treatment with repetitive transcranial magnetic stimulation. CONCLUSIONS: Findings suggest that electroconvulsive therapy is associated with transient negative cognitive side effects, most of which dissipate in the days after treatment. Deficits of this sort are not apparent after treatment with a 2-week course of repetitive transcranial magnetic stimulation.

Affect↗

PubMed2006

Cerebral metabolic effects of intravenous glycine in healthy human subjects.

Enhancing N-methyl-D-aspartate (NMDA) receptor function via increasing synaptic concentrations of glycine is currently investigated as a novel approach to treat schizophrenia. The neural correlates of enhanced NMDA receptor function in humans, however, are unclear to date. The present study determines the effects of intravenous administration of the glycine on regional cerebral metabolic rate of glucose (rCMRGlu) in healthy control subjects by using [18F]fluorodeoxyglucose and positron emission tomography and on neuropsychological behavioral measures. Thirteen healthy volunteers were recruited, and 12 subjects completed the protocol. These individuals participated in 1 magnetic resonance imaging study and 2 [18F]fluorodeoxyglucose positron emission tomography studies. In a double-blind, randomized, controlled, crossover design, participants received on one test day an intravenous glycine infusion and on the other test day a placebo infusion. There were no significant behavioral and neuropsychological effects of glycine compared with placebo. However, there was a significant reduction of whole-brain CMRGlu during administration of glycine compared with placebo (t = 2.60, df = 11, P = 0.023). In the a priori-selected regions of interest, there was a significant reduction in the cerebellum (t = -3.18, df = 11, P = 0.009) and the dorsolateral prefrontal cortex (t = -2.31, df = 11, P = 0.041). When corrected for whole-brain CMRGlu, rCMRGlu differences were not significant. This study suggests that studies of whole-brain cerebral metabolism may be useful for studying glycine-related mechanisms in healthy humans because there is not a clear cognitive or behavioral signal related to glycine administration at doses thought to be important clinically in patient populations.

Adult↗

PubMed2003

Functional imaging of cognition in Parkinson's disease.

PURPOSE OF REVIEW: Cognitive deficits that occur even early in the course of Parkinson's disease have received increasing attention in current imaging research. The exact physio-pathological processes mediating the deficits and the complex relationship of cognitive signs and antiparkinsonian treatment are not well understood. A clearer understanding of these mechanisms could potentially influence treatment choices, drug development and, ultimately, patient care. RECENT FINDINGS: Abnormal networks identified in studies of resting state metabolism in Parkinson's disease represent metabolic markers for remote effects of striato-nigral degeneration. These metabolic changes include subcortico-cortical networks, in particular cognitive cortico-striato-pallidal-thalamocortical loops. Recent brain studies focus on intervention-related brain changes. They illustrate different task-specific changes in brain activation with deep brain stimulation and with levodopa. Variable results of stimulation can be attributed to different effects on segregated cortico-striato-pallidal-thalamocortical loops during stimulation. By contrast, the heterogeneity observed in studies with levodopa possibly reflects the disease-stage and task-specific effects of levodopa. A decline in caudate dopamine modulated basal ganglia outflow appears to contribute to executive dysfunction and to brain activation changes in these loops at early Parkisnon's disease stages, while mesocortical degeneration mediated increases of inefficient dorsolateral prefrontal cortex activation may display a feature of more advanced disease stages only. SUMMARY: Despite evidence for the role of dopamine and cortico-striato-pallidal-thalamocortical loops in cognition, the specific contributions of mesocortical dopamine depletion and striatal dysfunction with downstream consequences on the loops remain to be separated. Additionally, more research is needed into the role of non-dopaminergic pathology in cognitive decline in Parkinson's disease.

Cerebral Cortex↗

PubMed2005

The effects of repetitive transcranial magnetic stimulation (rTMS) on procedural memory and dysphoric mood in patients with major depressive disorder.

OBJECTIVE: To study the effects of depression and treatment with repetitive transcranial magnetic stimulation (rTMS) on sequence learning. BACKGROUND: Prefrontal dysfunction in depression may affect sequence learning and be amenable to normalization by rTMS. METHOD: The serial reaction time test (SRTT) was administered to 19 patients with major depressive disorder (MDD) and 20 nondepressed control participants. MDD patients were examined before and following treatment with rTMS to the left dorsolateral prefrontal cortex in daily sessions of 1600 stimuli at 10 Hz and at an intensity of 110% of the motor threshold. Treatment occurred over a 2-week interval of time. RESULTS: MDD and nondepressed groups differed significantly with respect to baseline response speed. Following treatment with rTMS, MDD participants demonstrated significantly improved mood, improved response speed, and improved procedural learning. CONCLUSIONS: Findings suggest that rTMS over a 2-week period improves performance on tasks of response speed and procedural memory in patients with MDD. These cognitive effects are greater in those patients who showed a significant antidepressant effect to rTMS intervention.

Adult↗

PubMed2005

Differential brain activation according to chronic social reward frustration.

Neural correlates of reward frustration are increasingly studied in humans. In line with prediction error theory, omission of an expected reward is associated with relative decreases of cerebral activation in dopaminergic brain areas. We investigated whether a history of chronic work-related reward frustration influences this reward-dependent activation pattern by means of functional magnetic resonance imaging. Solving arithmetic tasks was followed by either monetary reward or omission of reward. Hyperactivations in the medial prefrontal, anterior cingulate and dorsolateral prefrontal cortex were observed in a group of healthy adults with high susceptibility to reward frustration as compared with a group with low susceptibility. Findings indicate a compromised ability of adapting brain activation among those suffering form chronic social reward frustration.

Adult↗

PubMed2005

Motor cortical excitability in depressive patients after electroconvulsive therapy and repetitive transcranial magnetic stimulation.

Electroconvulsive therapy (ECT) and repetitive transcranial magnetic stimulation (rTMS) of the dorsolateral prefrontal cortex are brain stimulation techniques that are used as therapeutic interventions in major depression. However, the exact therapeutic mode of action needs further clarification. In this case report, we describe the impact of these stimulation techniques on motor cortical excitability, as revealed by transcranial magnetic stimulation-elicited motor-evoked potentials in 2 patients who received consecutively both rTMS and ECT. Both patients showed a decrease in motor cortical excitability after response to antidepressant brain stimulation, whereas parameters of motor cortical excitability remained unchanged after the first non-successful intervention. These results suggest that both ECT and rTMS may have an impact on parameters of motor cortical neuronal excitability. Furthermore, measurement of motor cortical excitability may be a useful tool for investigating and monitoring inhibitory brain effects of different antidepressant stimulation techniques.

Adult↗

PubMed1991

Investigating a network model of word generation with positron emission tomography.

By using positron emission tomography (PET) we examined the biological validity of a network model describing changes in cerebral activity associated with intrinsic and extrinsic word generation. The production of words not specified by an extrinsic stimulus constitutes willed or intrinsic generation. Perceiving a heard word is an example of extrinsic generation. The model incorporates three neuronal systems: a pool that stores word representations in a distributed fashion, an afferent system conveying sensory input to the pool and a modulating system that alters the responsivity of neurons in the pool. Simulations based on the model suggested that intrinsic generation would be associated with low activity in the pool, consequent on reduced modulation, and extrinsic generation with high activity. We measured cerebral activity with PET during intrinsic (verbal fluency) and extrinsic (responding to heard words) word generation and found this pattern of changes in the left superior temporal region. We were able to designate this region the site of the distributed word store and implicate the left dorsolateral prefrontal cortex (DLPFC) as the source of modulation. The relation between the superior temporal gyrus and DLPFC was shown by examining the correlation between the two regions in terms of cerebral activity. We conclude that the left DLPFC is responsible for modulating the responsivity of a neural system in the superior temporal gyrus and is the probable mediator of changes in attentional and intentional states that underlies the intrinsic generation of words.

Animals↗