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Results for “Dorsolateral Prefrontal Cortex”

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PubMed1996

Cerebral activation during performance of a card sorting test.

The Wisconsin Card Sorting Test (WCST) is used clinically for evaluating frontal lobe function, but there is some controversy as to its specificity for detecting frontal lobe damage. To investigate the cerebral regions essential to the performance of the Card Sorting Test, we measured the regional cerebral blood flow (rCBF) in 18 normal subjects by PET under the three conditions: (i) during the Modified Card Sorting Test (MCST); (ii) during a matching-to-sample (MTS) task, based on the MCST, but with selective attention to one of three stimulus categories (colour, number or shape) as a control to cancel the effects of maintenance of sets in the MCST; (iii) under resting conditions as overall control. When rCBF during the MCST was compared with that during each MTS task separately, significant activations were observed during the MCST in the left or bilateral dorsolateral prefrontal cortex (DLPFC), bilateral inferior parietal lobes, left superior occipital gyrus and left cerebellum. Compared with all the MTS tasks inclusively, significant increase in rCBF was detected during the MCST in the bilateral DLPFC, inferior parietal lobes, striate cortex, cerebellum and left occipital cortex. These results suggest the involvement of the DLPFC and other related areas such as the inferior parietal cortex in the execution of the MCST, and may help explain why a variety of brain lesions can result in impaired performance on the Card Sorting Test.

Adult↗

PubMed1996

Frontal lobe dysfunction in amyotrophic lateral sclerosis. A PET study.

PET measurements of regional cerebral blood flow (rCBF) were used to explore frontal lobe dysfunction in amyotrophic lateral sclerosis (ALS). An activation paradigm of executive frontal lobe function (verbal fluency), which contrasted rCBF during word generation and word repetition, was used. Two groups of ALS patients, defined by the presence or absence of cognitive impairment (ALSi) (impaired, n = 6: ALSu unimpaired, n = 6) were compared with healthy age-matched controls (n = 6). Patient selection was based on prior performance on a written test of verbal fluency. Additional neuropsychological assessment of the patients revealed evidence of executive and memory dysfunction in the ALSi group only, with marked deficits in tests of intrinsic generation. The ALSi patients displayed significantly (P < 0.001) impaired activation in cortical and subcortical regions including the dorsolateral prefrontal cortex (DLPFC; areas 46 and 9), lateral premotor cortex (areas 8 and 6), medial prefrontal and premotor cortices (areas 8 and 9), insular cortex bilaterally and the anterior thalamic nuclear complex. Although the three groups showed matched word generation performance on the scanning paradigm, the ALSu group displayed a relatively unimpaired pattern of activation. These results support the presence of extra-motor neuronal involvement, particularly along a thalamo-frontal association pathway, in some non-demented ALS patients. In addition, this study suggests dysfunction of DLPFC in some ALS patients with associated cognitive impairments.

Aged↗

PubMed1999

Context-dependent, neural system-specific neurophysiological concomitants of ageing: mapping PET correlates during cognitive activation.

We used PET to explore the neurophysiological changes that accompany cognitive disability in ageing, with a focus on the frontal lobe. Absolute regional cerebral blood flow (rCBF) was measured in 41 healthy volunteers, evenly distributed across an age range of 18-80 years, during two task paradigms: (i) the Wisconsin Card Sorting Test (WCST), which depends heavily on working memory and is particularly sensitive to dysfunction of the dorsolateral prefrontal cortex (DLPFC); and (ii) Raven's Progressive Matrices (RPM), which may also have a working memory component, but depends more on visuo-spatial processing and is most sensitive to dysfunction of postrolandic regions. We used voxel-wise correlational mapping to determine age-related changes in WCST and RPM activation and developed a method to quantitate and localize statistical differences between the correlation maps for the two task paradigms. Because both WCST and RPM performance declined with age, as expected, correlational analyses were performed with and without partialling out the effect of task performance. Task-specific reductions of rCBF activation with age were found in the DLPFC during the WCST and in portions of the inferolateral temporal cortex involved in visuo-spatial processing during the RPM. We also found reduced ability to suppress rCBF in the right hippocampal region during the WCST and in mesial and polar portions of the prefrontal cortex during both task conditions. Task-dependent alterations with age in the relationship between the DLPFC and the hippocampus were also documented; because the collective pattern of changes in the hippocampal-DLPFC relationship with ageing was opposite to that seen in a previous study using dextroamphetamine, we postulated a dopaminergic mechanism. These results indicate that, despite some cognitive overlap between the two tasks and the age-related cognitive decline in both, many of the changes in rCBF activation with age were task-specific, reflecting functional alteration of the different neural circuits normally engaged by young subjects during the WCST and RPM. Reduced activation of areas critical for task performance (i.e. the DLPFC during the WCST and posterior visual association areas of the inferolateral temporal cortex during the RPM), in conjunction with the inability to suppress areas normally not involved in task performance (i.e. the left hippocampal region during the WCST and mesial polar prefrontal cortex during both the WCST and RPM), suggest that, overall, reduced ability to focus neural activity may be impaired in older subjects. The context dependency of the age-related changes is most consistent with systems failure and disordered connectivity.

Adolescent↗

PubMed2002

The functional significance of perinatal corpus callosum damage: an fMRI study in young adults.

We used functional MRI (fMRI) to establish the functional significance of corpus callosum damage in young adults who had been born very preterm. Seven subjects from a cohort of individuals who had been born at <33 weeks gestation and who had sustained callosal damage visualized on structural MRI were compared while they carried out auditory and visual tasks requiring callosal transfer with nine very preterm subjects with corpora callosa of normal appearance on structural MRI, and with seven full-term controls. The very preterm subjects with damaged corpora callosa had significantly different activation patterns compared with the two control groups. In the visual task, additional activity was seen in the right dorsolateral prefrontal cortex of the damaged callosum group, possibly because the task was accomplished by storing information in working memory. On the auditory task, a deficit of activity was seen in the right temporal lobe of the callosum group. The findings reveal a plasticity of function compensating for early damage to the corpus callosum.

Adolescent↗

PubMed2002

Excessive recruitment of neural systems subserving logical reasoning in schizophrenia.

Schizophrenic patients generally perform poorly on tasks that address executive functions. According to several imaging studies, the dorsolateral prefrontal cortex is hypoactive in schizophrenic patients during these tasks. It is not, however, clear whether this finding is associated more with impaired performance than with the illness itself, as performance has not been taken into account. We examined brain activity associated with executive function in schizophrenia using an experimental fMRI design that reveals performance effects, enabling correction for performance differences between groups. As this approach has not been reported before, and because brain function can be affected by medication, the effect of antipsychotic medication was also investigated. A task was used that requires logical reasoning, alongside a closely matched control task. Performance was accounted for by including individual responses in fMRI image analyses, as well as in group-wise analysis. Effects of medication were addressed by comparing medication-naïve patients and patients on atypical antipsychotic medication with healthy controls in two separate experiments. Imaging data were analysed with a novel, performance-driven method, but also with a method that is similar to that used in earlier studies, which reported hypofrontality. A modest reduction in performance was found in both patient groups. Brain activity associated with logical reasoning was correlated positively with performance in all groups. In patients on medication, activity did not differ from that in controls after correcting for difference in performance. In contrast, performance-corrected activity was significantly elevated in medication-naïve patients. This study indicates that schizophrenia may be associated with excessive recruitment of brain systems during logical reasoning. Considering the fact that performance was reduced in the patients, we argue that the efficiency of neural communication may be affected by the illness. It appears that in patients on atypical antipsychotic medication, this neural inefficiency is normalized. The study shows that performance is an important factor in the interpretation of differences between schizophrenic patients and controls. The reported association between performance and brain activity is relevant to clinical imaging studies in general.

Adult↗

PubMed2004

fMRI correlates of state and trait effects in subjects at genetically enhanced risk of schizophrenia.

Schizophrenia is a highly heritable disorder that typically develops in early adult life. Structural imaging studies have indicated that patients with the illness, and to some extent their unaffected relatives, have subtle deficits in several brain regions, including prefrontal and temporal lobes. It is, however, not known how this inherited vulnerability leads to psychosis. This study used a covert verbal initiation fMRI task previously shown to elicit frontal and temporal activity (the Hayling sentence completion task) to examine this issue. A large (n = 69) number of young participants at high risk of developing schizophrenia for genetic reasons took part, together with a matched group of healthy controls (n = 21). At the time of investigation, none had any psychotic disorder, but on detailed interview some of the high-risk participants (n = 27) reported isolated psychotic symptoms. The study aimed to determine: (i) whether there were activation differences that occurred in all subjects with a genetic risk of schizophrenia (i.e. 'trait' effects); and (ii) whether there were activation differences that only occurred in those at high risk who had isolated psychotic symptoms ('state' effects). No activation differences were found in regions commonly reported to be abnormal in the established illness, namely the dorsolateral prefrontal cortex or in the temporal lobes, but group differences of apparent genetic cause were evident in medial prefrontal, thalamic and cerebellar regions. In addition, differences in activation in those with symptoms were found in the intraparietal sulcus. No significant differences in performance were found between the groups, and all subjects were antipsychotic naïve. These findings therefore suggest that vulnerability to schizophrenia may be inherited as a disruption in a fronto-thalamic-cerebellar network, and the earliest changes specific to the psychotic state may be related to hyperactivation in the parietal lobe.

Adult↗

PubMed2004

Globus pallidus internus stimulation in primary generalized dystonia: a H215O PET study.

Globus pallidus internus (GPi) deep brain stimulation (DBS) increasingly shows promising efficacy in the treatment of severe primary generalized dystonia. Functional imaging studies have shown previously that dystonia could be related to abnormal cortical activation during voluntary movement. In the present study, the effects of GPi DBS on regional cerebral blood flow (rCBF) during a motor task were studied in patients with primary generalized dystonia. rCBF was measured using H215O and PET in eight control subjects and six patients with dystonia treated with bilateral GPi DBS. Subjects were scanned at rest and while performing joystick movements. Dystonic patients were tested in two conditions: 'OFF' (stimulator bilaterally switched off) and 'ON' (unilateral stimulation). In the 'OFF' condition, compared with rest, motor activation of the most dystonic hand was associated with overactivity in the contralateral dorsolateral prefrontal cortex, gyrus frontalis medialis, superior frontal gyrus (area 10), frontoorbital cortex and thalamus. In the 'ON' condition, GPi DBS contralaterally to the most dystonic hand induced a decrease of the overactivation in the same areas, as well as the putamen. According to the present study, generalized dystonia is associated with prefrontal overactivation which can be reversed by effective GPi DBS.

Adolescent↗

PubMed2005

Functional disconnectivity in subjects at high genetic risk of schizophrenia.

Schizophrenia is a highly heritable psychotic disorder. It has been suggested that deficits of the established state arise from abnormal interactions between brain regions. We sought to examine whether such connectivity abnormalities would be present in subjects at high genetic risk for the disorder. Functional connectivity analysis was carried out on functional MRI images from 21 controls and 69 high risk subjects performing the Hayling sentence completion task; 27 high risk subjects reported isolated psychotic symptoms, the remaining high risk subjects and controls did not. There were no significant differences in task performance between the groups. Based on previous findings we hypothesized: (i) state-related differences in connectivity between dorsolateral prefrontal cortex and lateral temporal lobe; (ii) genetically mediated reductions in a medial prefrontal-thalamic-cerebellar network; and (iii) increased prefrontal-parietal connectivity in high risk subjects (to a greater extent in those with isolated psychotic symptoms). Connectivity analysis was performed in two ways: with and without variance associated with task effects modelled and removed from the data. We did not find evidence to support our first hypothesis with either analysis method. However, consistent with hypothesis (ii), decreased connectivity between right medial prefrontal regions and contralateral cerebellum was found. This was only statistically significant in the analysis with task effects modelled and removed from the data. Finally, consistent with hypothesis (iii), increased connectivity between the left parietal and left prefrontal regions in high risk subjects was found in both analyses. These results, all in a situation uncontaminated by the effects of anti-psychotic medication, performance differences and prolonged illness, suggest there are abnormalities in functional connectivity over and above those attributable to task effects in high risk subjects. These connectivity abnormalities may underlie the diverse deficits seen in the established condition and the more subtle deficits seen in close relatives of those with the disorder.

Adolescent↗

PubMed2005

Object working memory deficits predicted by early brain injury and development in the preterm infant.

Children born preterm and of very low birth weight are at increased risk of learning difficulties and educational under-achievement. However, little is known about the specific neuropsychological problems facing these children or their neurological basis. Using prospective longitudinal data from a regional cohort of 92 preterm and 103 full-term children, this study examined relations between term MRI measures of cerebral injury and structural brain development and children's subsequent performance on an object working memory task at the age of 2 years. Results revealed clear between-group differences, with preterm children having greater difficulty encoding new information in working memory than term control children. Within the preterm group, task performance at the age of 2 years was related to both qualitative MRI measures of white matter (WM) injury and quantitative measures of total and regional brain volumes assessed at term equivalent. Bilateral reductions in total tissue volumes (%region) of the following cerebral regions were specifically related to subsequent working memory performance: dorsolateral prefrontal cortex, sensorimotor, parietooccipital and premotor. Associations between total cerebral tissue volumes at term (adjusted and unadjusted for intracranial volume) persisted even after the effects of WM injury were taken into account. This suggests that early disturbance in cerebral development may have an independent adverse impact on later working memory function in the preterm infant. These findings add to our understanding of the neuropathological pathways associated with later executive dysfunction in the very preterm infant.

Brain↗

PubMed2006

fMRI revealed neural substrate for reversible working memory dysfunction in subclinical hypothyroidism.

Cognitive impairments have been found in thyroid hormone-related diseases (e.g. hyperthyroidism and hypothyroidism) for a long time. However, whether and how subclinical hypothyroidism (SCH) causes any deficits in brain functions, and whether a hormone-replacement treatment is necessary for SCH patients, still remain controversial subjects. In the present study, functional MRI (fMRI) was used to measure brain functions by asking euthyroid subjects, hyperthyroid patients and SCH patients to perform the widely used digit n-back working memory task. After having been treated with l-thyroxine for approximately 6 months, the SCH patients were asked to do the same fMRI experiment. The hypothyroid and SCH patients scored significantly lower in the 2-back task than either the hyperthyroid patients or the euthyroid subjects (P < 0.012). The fMRI showed that a common frontoparietal network, including bilateral middle/inferior frontal gyri (M/IFG), bilateral dorsolateral prefrontal cortex (DLPFC), bilateral premotor areas (PreMA), the supplementary motor area/anterior cingulate cortex (SMA/ACC) and bilateral parietal areas (PA), was activated by the n-back task in all the subjects. Further quantitative analysis showed that the load effect of blood oxygen level-dependent (BOLD) response appeared in all the five regions of interest (ROIs) in the euthyroid and hyperthyroid subjects. In the pre-treatment SCH patients, however, the load effect of BOLD response was only found in the PA and PreMA, but not in other frontal cortex ROIs [general linear model (GLM), F < 2.6, P > 0.1]. After an approximately 6 month treatment with LT4, the SCH patients exhibited the same load effects in all five ROIs as the euthyroid subjects (GLM, F > 6, P < 0.05) along with an improvement of performance in n-back task. These results suggest that working memory (but not other memory functions) is impaired in SCH patients, mainly as far as disorders of the frontoparietal network were concerned. Both the memory performance and frontal executive functions were improved after an l-thyroxine-replacement treatment.

Adolescent↗

PubMed2006

Mixing pro- and antisaccades in patients with parkinsonian syndromes.

Prosaccades and antisaccades were investigated in three groups of patients with parkinsonian syndromes, Parkinson's disease, corticobasal degeneration (CBD) and progressive supranuclear palsy (PSP), and in a control group. Saccade tasks were performed in single-task blocks (i.e. either blocks of prosaccades or blocks of antisaccades) and in mixed-task blocks (i.e. in blocks of randomly interleaved pro- and antisaccades). Saccade latencies and directional errors (misdirected saccades) were analysed in each subject, and we concentrated more specifically on the comparison of error rates in single tasks and in repeated trials of mixed tasks (i.e. mixing costs). The performance of each group in single tasks was largely consistent with previous studies, with normal antisaccade error rates in Parkinson's disease and CBD patients and increased antisaccade error rates in PSP patients. In contrast, a double dissociation was observed in mixed tasks. Parkinson's disease and CBD patients showed a marked increase in prosaccade and antisaccade error rates in repeated trials of mixed tasks, illustrated by increased mixing costs, whereas PSP patients showed similar error rates in single and repeated trials of mixed tasks, i.e. normal mixing costs. These results demonstrate that: (i) antisaccade performances may be differentially affected in mixed tasks and single tasks; (ii) the region of the dorsolateral prefrontal cortex which is crucial for reflexive saccade inhibition does not seem to be involved in the additional processes required in mixed-task conditions; (iii) the study of interleaved pro- and antisaccades may increase the accuracy of the differential diagnosis between these parkinsonian syndromes.

Aged↗

PubMed2000

Cortical connections of the insular and adjacent parieto-temporal fields in the cat.

We present a comprehensive analysis of the cortical connections of the insular and adjacent cortical areas in the domestic cat by using microinjections of wheat-germ agglutinin conjugated to horseradish peroxidase. We examined the identity and extent of the cortical fields connected to each area, the relative anatomical weights of the various connections, their laminar origin, and their paths across the cerebral commissures. Our main finding is that despite their relatively small size and close apposition, the connections of the insular and adjacent areas are far more widespread and more specific to each area than previously realized, suggesting that each area is involved in disparate aspects of cortical integration. The granular insular area is linked to a constellation of somatosensory, motor, premotor and prefrontal districts. The dysgranular insular area is chiefly associated with lateral prefrontal and premotor, lateral somatosensory and perirhinal cortices. The dorsal agranular insular area is connected with limbic neocortical fields, while the ventral agranular insular area is associated with an array of olfactory allocortical fields. The anterior sylvian area is associated with visual, auditory and multimodal areas, with the dorsolateral prefrontal cortex, and with perirhinal area 36. The parainsular area is linked to non-tonotopic auditory and ventromedial frontal areas. Trajectories followed by the callosal axons of each of the investigated areas are extremely divergent. As a whole, the picture of the insular region that emerges from this and a parallel study (Clascá et al., J Comp Neurol 384:456-482, 1997) is that of an extreme heterogeneity, both in terms of histological architecture and neural connections. Comparison with earlier published reports on primates suggests that most, but not all, of the areas we investigated in cats may have an direct counterpart within the insula of Old World monkeys.

Afferent Pathways↗

PubMed2001

Enhanced or impaired cognitive function in Parkinson's disease as a function of dopaminergic medication and task demands.

We investigated how dopamine (DA) systems contribute to cognitive performance in the domain of learning and attentional flexibility by examining effects of withdrawing DA-ergic medication in patients with Parkinson's disease (PD). Medication remediated impairments in switching between two tasks, thought to depend on circuitry connecting the dorsolateral prefrontal cortex and the posterior parietal cortex to the dorsal caudate nucleus, which is profoundly DA-depleted in PD. By contrast, the same medication impaired probabilistic reversal learning that implicates orbitofrontal cortex- ventral striatal circuitry, which is relatively spared of DA loss in PD. Hence, DA-ergic medication improves or impairs cognitive performance depending on the nature of the task and the basal level of DA function in underlying cortico-striatal circuitry.

Attention↗

PubMed2001

Parieto-frontal interactions in visual-object and visual-spatial working memory: evidence from transcranial magnetic stimulation.

This study aimed to investigate whether transcranial magnetic stimulation (TMS) can induce selective working memory (WM) deficits of visual-object versus visual-spatial information in normal humans. Thirty-five healthy subjects performed two computerized visual n-back tasks, in which they were required to memorize spatial locations or abstract patterns. In a first series of experiments, unilateral or bilateral TMS was delivered on posterior parietal and middle temporal regions of both hemispheres after various delays during the WM task. Bilateral temporal TMS increased reaction times (RTs) in the visual-object, whereas bilateral parietal TMS selectively increased RTs in the visual-spatial WM task. These effects were evident at a delay of 300 ms. Response accuracy was not affected by bilateral or unilateral TMS of either cortical region. In a second group of experiments, bilateral TMS was applied over the superior frontal gyrus (SFG) or the dorsolateral prefrontal cortex (DLPFC). TMS of the SFG selectively increased RTs in the visual-spatial WM task, whereas TMS of the DLPFC interfered with both WM tasks, in terms of both accuracy and RTs. These effects were evident when TMS was applied after a delay of 600 ms, but not one of 300 ms. These findings confirm the segregation of WM buffers for object and spatial information in the posterior cortical regions. In the frontal cortex, the DLPFC appears to be necessary for WM computations regardless of the stimulus material.

Adult↗

PubMed2002

Oculomotor effects of delta-9-tetrahydrocannabinol in humans: implications for the functional neuroanatomy of the brain cannabinoid system.

The significance of cannabinoid signaling for human cognition and motor control is still poorly understood. Here, we have investigated acute behavioral effects of oral delta-9-tetrahydrocannabinol (THC) with oculomotor paradigms in 12 healthy human subjects. Compared to baseline testing: (i) THC increased latencies of reflexive visually guided saccades, while their accuracy was not affected; (ii) latencies of memory-guided saccades were unaffected, but THC modulated accuracy of these eye movements by increasing average gain and gain variability; (iii) frequency of anticipated memory-guided saccades and antisaccade errors was increased; (iv) the saccade amplitude/peak velocity relationships were not affected. These results show that THC acts on selected aspects of saccade control, namely spatial attention shifts, fine tuning of volitional saccades, spatial working memory and inhibition of inappropriate saccades. The pattern of effects suggests modulation of neuronal activity in substantia nigra pars reticulata and/or dorsolateral prefrontal cortex and sparing of the eye fields and the final motor pathway for saccades. Behaviorally, our findings reflect the distribution of CB-1 cannabinoid receptors in the human neocortex, basal ganglia and brainstem and provide evidence for participation of the cannabinoidergic system in high level control of saccades and associated cognitive functions. Saccadic eye movements may provide an objective measure of motor and cognitive effects of cannabinoids.

Adult↗

PubMedDate not supplied

Active representation of shape and spatial location in man.

Neural activity during the delay period of spatial delayed response (DR) and delayed matching (DM) tasks was investigated by positron emission tomography. A distributed cortical system was activated in each condition. The bilateral dorsolateral prefrontal cortex (DLPFC) was activated in the delay period of both tasks; activation was of higher significance on the right in the DR task and the left in the DM task, and extended to the anterolateral prefrontal cortex in the DM condition. Active representation of spatial location in the DR task was associated with co-activation of the medial and lateral parietal cortex and the extrastriate visual cortex. Active representation of shape in the DM task was associated with co-activation of medial and lateral parietal cortex and the inferior temporal cortex. Response-related activity was observed in both tasks. Activation of anterior cingulate, inferior frontal, lateral promotor and rostral inferior parietal cortex was observed in the DR condition, a task characterized by preparation of a movement to a predetermined location. In contrast, preparation to move to an undetermined location in the DM task was associated with activation predominantly in rostral SMA.

Adolescent↗

PubMedDate not supplied

Physiological characteristics of capacity constraints in working memory as revealed by functional MRI.

A fundamental characteristic of working memory is that its capacity to handle information is limited. While there have been many brain mapping studies of working memory, the physiological basis of its capacity limitation has not been explained. We identified characteristics of working memory capacity using functional magnetic resonance imaging (fMRI) in healthy subjects. Working memory capacity was studied using a parametric 'n-back' working memory task involving increasing cognitive load and ultimately decreasing task performance. Loci within dorsolateral prefrontal cortex (DLPFC) evinced exclusively an 'inverted-U' shaped neurophysiological response from lowest to highest load, consistent with a capacity-constrained response. Regions outside of DLPFC, in contrast, were more heterogeneous in response and often showed early plateau or continuously increasing responses, which did not reflect capacity constraints. However, sporadic loci, including in the premotor cortex, thalamus and superior parietal lobule, also demonstrated putative capacity-constrained responses, perhaps arising as an upstream effect of DLPFC limitations or as part of a broader network-wide capacity limitation. These results demonstrate that regionally specific nodes within the working memory network are capacity-constrained in the physiological domain, providing a missing link in current explorations of the capacity characteristics of working memory.

Adolescent↗

PubMedDate not supplied

From perception to action: temporal integrative functions of prefrontal and parietal neurons.

The dorsolateral prefrontal cortex (DPFC) and the posterior parietal cortex (PPC) are anatomically and functionally interconnected, and have been implicated in working memory and the preparation for behavioral action. To substantiate those functions at the neuronal level, we designed a visuomotor task that dissociated the perceptual and executive aspects of the perception-action cycle in both space and time. In that task, the trial-initiating cue (a color) indicated with different degrees of certainty the direction of the correct manual response 12 s later. We recorded extracellular activity from 258 prefrontal and 223 parietal units in two monkeys performing the task. In the DPFC, some units (memory cells) were attuned to the color of the cue, independent of the response-direction it connoted. Their discharge tended to diminish in the course of the delay between cue and response. In contrast, few color-related units were found in PPC, and these did not show decreasing patterns of delay activity. Other units in both cortices (set cells) were attuned to response-direction and tended to accelerate their firing in anticipation of the response and in proportion to the predictability of its direction. A third group of units was related to the determinacy of the act; their firing was attuned to the certainty with which the animal could predict the correct response, whatever its direction. Cells of the three types were found closely intermingled histologically. These findings further support and define the role of DPFC in executive functions and in the temporal closure of the perception-action cycle. The findings also agree with the involvement of PPC in spatial aspects of visuomotor behavior, and add a temporal integrative dimension to that involvement. Together, the results provide physiological evidence for the role of a prefrontal-parietal network in the integration of perception with action across time.

Animals↗