The ups and downs of repetition: Modulation of the perirhinal cortex by conceptual repetition predicts priming and long-term memory

In order to better understand how concepts might be represented in the brain, we used a cross-modal conceptual priming paradigm to examine how repetition-related activity changes in the brain are related to conceptual priming. During scanning, subjects made natural/manmade judgments on a continuous stream of spoken nouns, written nouns and pictures of objects. Each stimulus either repeated in the same or a different modality with 1–4 intervening trials between repetitions. Behaviorally, participants showed significant perceptual and conceptual priming effects. The fMRI data showed that the conditions associated with the greatest behavioral priming exhibited the largest decreases in BOLD activity in left perirhinal cortex (PRc), as well as a few other regions. Furthermore, the PRc was the only region to show this relationship for the cross-modal conditions alone, where the concept but not the percept repeated. Conversely, repetition-related increases in PRc activity predicted better subsequent memory as assessed by a post-scan recognition test. These results suggest that repetition-related activity changes in the PRc are related both to the speed of access to a repeated concept and to that concept's later memorability.     

Preferential responses to faces in superior temporal and medial prefrontal cortex in three-year-old children

Perceiving faces and understanding emotions are key components of human social cognition. Prior research with adults and infants suggests that these social cognitive functions are supported by superior temporal cortex (STC) and medial prefrontal cortex (MPFC). We used functional near-infrared spectroscopy (fNIRS) to characterize functional responses in these cortical regions to faces in early childhood. Three-year-old children (n = 88, M(SD) = 3.15(.16) years) passively viewed faces that varied in emotional content and valence (happy, angry, fearful, neutral) and, for fearful and angry faces, intensity (100%, 40%), while undergoing fNIRS. Bilateral STC and MPFC showed greater oxygenated hemoglobin concentration values to all faces relative to objects. MPFC additionally responded preferentially to happy faces relative to neutral faces. We did not detect preferential responses to angry or fearful faces, or overall differences in response magnitude by emotional valence (100% happy vs. fearful and angry) or intensity (100% vs. 40% fearful and angry). In exploratory analyses, preferential responses to faces in MPFC were not robustly correlated with performance on tasks of early social cognition. These results link and extend adult and infant research on functional responses to faces in STC and MPFC and contribute to the characterization of the neural correlates of early social cognition.     

Social appraisal in chronic psychosis: Role of medial frontal and occipital networks

Persons with schizophrenia often appraise other individuals as threatening or persecutory. To evaluate social appraisal in schizophrenia, we probed brain networks with a task in which subjects judged whether or not they liked face stimuli with emotional expressions. We predicted that appraising negative expressions would engage patients, more than controls, and negative faces would be related to higher levels of negative affect and produce increased activity in the medial frontal cortex, an area involved in social appraisal. Twenty-one stable outpatients with chronic non-affective psychosis (16 schizophrenic, 5 schizoaffective) and 21 healthy subjects underwent functional magnetic resonance imaging. Compared with the control subjects, patients were slower to respond, but particularly slow when they judged negatively-valenced faces, a slowness correlated with negative affect in the psychosis patients. Appraisal activated the medial prefrontal cortex (mPFC) across all face valences. For negative expressions, patients exhibited greater activation of the dorsal anterior cingulate cortex (dACC). A psychophysiological interaction analysis of the dACC revealed co-modulation of the mPFC in controls, significantly less in patients, and a trend for co-modulation of occipital cortex in the patients. Activity in occipital cortex correlated with poor social adjustment and impaired social cognition, and co-modulation of the occipital gyrus by the dACC was correlated with poorer social cognition. The findings link appraisal of negative affect with aberrant activation of the medial frontal cortex, while early sensory processing of this social cognitive task was linked with poor social function, reflecting either top-down or bottom-up influences.     

Cerebral cortex and amino acid neurotransmitters: Higher levels of aspartic acid but not GABA in the frontal cortex of the rat

Endogenous levels of Aspartic acid, GABA and Glutamic acid plus Glutamine were measured in the frontal, occipital, temporal and parietal cortex. Aspartic acid levels were found higher in the frontal cortex than in the rest of the cortical areas studied. GABA, however, had a homogenous distribution among all cortical areas.     

A role for acetylcholine in conditioning-related responses of rat frontal cortex neurons: microiontophoretic evidence

In an associative conditioning paradigm, an auditory stimulus (CS+) was paired with rewarding medial forebrain bundle stimulation or a tone of different frequency (CS-) was presented without pairing. After training, slow potential (SP) and single neuron responses were recorded from rat frontal cortex. When cortical SP responses indicated the development of discrimination between CS+ and CS- tones, single neurons could be isolated that exhibited a discriminative response to CS+. Seventy-three percent of the 56 neurons which discriminated between CS+ and CS- were excited by the paired tone while the remainder were inhibited. Iontophoretically applied acetylcholine increased spontaneous firing rate in 90% of the excited cells and 87% of the inhibited cells. Iontophoretic administration of a muscarinic receptor antagonist, either atropine or tropicamide, during trial presentation attenuated the conditioning-related response to CS+ as well as the response to acetylcholine in the majority of neurons. The largest group of discriminating neurons were excited by both CS+ and acetylcholine, and both responses were suppressed by the antagonists. The results provide evidence that conditioning-related responses of a major population of frontal cortex neurons are modulated by cholinergic input, a portion of which may originate in the basal forebrain area. There also may be a significant non-cholinergic influence on these neuronal responses.     

Evidence for 5-HT4 receptor involvement in the enhancement of acetylcholine release by p-chloroamphetamine in rat frontal cortex

The roles of endogenous serotonin (5-HT) and 5-HT receptor subtypes in regulation of acetylcholine (ACh) release in frontal cortex of conscious rats were examined using a microdialysis technique. Systemic administration (1 and 3 mg/kg, i.p.) of the 5-HT-releasing agent p-chloroamphetamine (PCA) elevated ACh output in a dose-dependent manner. Depletion of endogenous 5-HT by p-chlorophenylalanine significantly attenuated the facilitatory effect of PCA on ACh release. The PCA (3 mg/kg)-induced increase in ACh release was significantly inhibited by local application of the 5-HT₄ receptor antagonists RS23597 (50 μM) and GR113803 (1 μM), while the 5-HT_1A antagonist WAY-100135 (10 mg/kg, i.p.; 100 μM), 5-HT_1A/1B/β-adrenoceptor antagonists (−)-pindolol (8 mg/kg, i.p.) and (−)-propranolol (150 μM), 5-HT_2A/2C antagonist ritanserin (1 mg/kg, i.p.; 10 μM) and 5-HT₃ antagonist ondansetron (1 mg/kg, i.p.; 10 μM) failed to significantly modify the effect of PCA. These results suggest that PCA-induced enhancement of 5-HT transmission facilitates ACh release from rat frontal cortex at least in part through 5-HT₄ receptors.     

Evidence for involvement of the frontal cortex in pain-related cerebral events in cats: increase in local cerebral blood flow by noxious stimuli

Noxious stimuli were shown to induce a remarkable increase in local cerebral blood flow restricted to the forepart of the cerebral hemispheres bilaterally anterior to the posterior sigmoid gyrus in cats. This increase in local cerebral blood flow was averted by lesions in the bilateral ventromedial thalamus and attenuated by pretreatment with an intraventricular injection of 6-hydroxydopamine.     

The effect of ACPD on the responses to NMDA and AMPA varies with layer in slices of rat visual cortex

The effect of 1S,3R-aminocyclopentane dicarboxylic acid (ACPD) was measured on cells from various layers in slices of the rat visual cortex using whole-cell recording techniques. The position of the recorded cell was estimated by distance from pia to the layer VI/white matter boundary, and verified in 34/97 cells by staining with biocytin. Potentiation or depression of the responses to NMDA and AMPA by the metabotropic glutamate agonist ACPD was examined by iontophoresis of the drugs close to the cell body. Iontophoresis of ACPD had different effects in different layers. In layer VI, ACPD produced a substantial depolarization, which augmented the responses to NMDA and AMPA. In layer V, ACPD did not produce a significant depolarization, but potentiated the response to NMDA and AMPA. In layer IV, ACPD produced a small hyperpolarization, and depressed the response to NMDA. In layers II and III, the results were small and variable. Most recordings from stained cells were from pyramidal cells. Where recordings from non-pyramidal cells were obtained (3/34), results were the same as from pyramidal cells in the same layer. The same results were obtained when tetrodotoxin was in the bath solution. We conclude that the potentiation or depression of the response to NMDA and AMPA by ACPD varies with layer in rat visual cortex.     

Using real-time fMRI neurofeedback to restore right occipital cortex activity in patients with left visuo-spatial neglect: proof-of-principle and preliminary results

Hemineglect is common after right parietal stroke, characterised by impaired awareness for stimuli in left visual space, with suppressed neural activity in the right visual cortex due to losses in top-down attention signals. Here we sought to assess whether hemineglect patients are able to up-regulate their right visual cortex activity using auditory real-time functional magnetic resonance imaging (rt-fMRI) neurofeedback. We also examined any effect of this training procedure on neglect severity. Two different neurofeedback methods were used. A first group of six patients was trained to up-regulate their right visual cortex activity and a second group of three patients was trained to control interhemispheric balance between their right and left visual cortices. Over three sessions, we found that the first group successfully learned to control visual cortex activity and showed mild reduction in neglect severity, whereas the second group failed to control the feedback and showed no benefit. Whole brain analysis further indicated that successful up-regulation was associated with a recruitment of bilateral fronto-parietal areas. These findings provide a proof of concept that rt-fMRI neurofeedback may offer a new approach to the rehabilitation of hemineglect symptoms, but further studies are needed to identify effective regulation protocols and determine any reliable impact on clinical symptoms.     

Somatosensory cortex responses to median nerve stimulation: fMRI effects of current amplitude and selective attention.

OBJECTIVES: The aim of this study was to localize and to investigate response properties of the primary (SI) and the secondary (SII) somatosensory cortex upon median nerve electrical stimulation. METHODS: Functional magnetic resonance imaging (fMRI) was used to quantify brain activation under different paradigms using electrical median nerve stimulation in healthy right-handed volunteers. In total 11 subjects were studied using two different stimulus current values in the right hand: at motor threshold (I(max)) and at I(min) (1/2 I(max)). In 7 of these 11 subjects a parametric study was then conducted using 4 stimulus intensities (6/6, 5/6, 4/6 and 3/6 I(max)). Finally, in 10 subjects an attention paradigm in which they had to perform a counting task during stimulation with I(min) was done. RESULTS: SI activation increased with current amplitude. SI did not show significant activation during stimulation at I(min). SII activation did not depend on current amplitude. Also the posterior parietal cortex appeared to be activated at I(min). The I(min) response in SII significantly increased by selective attention compared to I(min) without attention. At I(max) significant SI activity was observed only in the contralateral hemisphere, the ipsilateral cerebellum, while other areas possibly showed bilateral activation. CONCLUSIONS: Distributed activation in the human somatosensory cortical system due to median nerve stimulation was observed using fMRI. SI, in contrast to SII, appears to be exclusively activated on the contralateral side of the stimulated hand at I(max), in agreement with the concept of SI's important role in processing of proprioceptive input. Only SII remains significantly activated in case of lower current values, which are likely to exclusively stimulate the sensible fibres mediating cutaneous receptor input. Selective attention only enhances SII activity, indicating a higher-order role for SII in the processing of somatosensory input.     

Phase locking of neuronal responses to the vertical refresh of computer display monitors in cat lateral geniculate nucleus and striate cortex

The proliferation of low-cost microcomputer systems has led to the use of these systems as alternatives to expensive display devices for visual physiology and psychophysics experiments. The video displays of these systems often lack the flexibility of achieving wide linear luminance ranges and high vertical refresh rates — two parameters which may influence data acquisition. We have examined the responses of neurons and pairs of neurons in cat LGN and striate cortex to bar and sinusoidal grating stimuli generated by a conventional PC-based VGA graphics card and displayed on a NEC Multisync + color monitor with a 60 Hz vertical (display) refresh rate. Responses to these stimuli were autocorrelated and power spectral densities (PSD) were calculated, revealing that the majority of simple and complex cortical cells and nearly all LGN cells exhibited significant peaks in their autocorrelations at 16.7 ms and in the PSD at 60 Hz. Responses to identical stimuli generated with an optical bench using an incandescent light source contained no power at 60 Hz. Furthermore, cross-correlations between the spike trains of neuron-pairs were severely contaminated by peaks directly attributable to the entrainment of the two elements of the pair to the vertical refresh signal. Thus, we suggest that the use of conventional computer displays introduces a temporal artifact into neuronal spike trains in both single and multiple spike train analysis.     

Cerebellar modulation of frontal cortex dopamine efflux in mice: relevance to autism and schizophrenia

Cerebellar and frontal cortical pathologies have been commonly reported in schizophrenia, autism, and other developmental disorders. Whether there is a relationship between prefrontal and cerebellar pathologies is unknown. Using fixed potential amperometry, dopamine (DA) efflux evoked by cerebellar or, dentate nucleus electrical stimulation (50 Hz, 200 muA) was recorded in prefrontal cortex of urethane anesthetized lurcher (Lc/+) mice with 100% loss of cerebellar Purkinje cells and wildtype (+/+) control mice. Cerebellar stimulation with 25 and 100 pulses evoked prefrontal cortex DA efflux in +/+ mice that persisted for 12 and 25 s poststimulation, respectively. In contrast, 25 pulse cerebellar stimulation failed to evoke prefrontal cortex DA efflux in Lc/+ mice indicating a dependency on cerebellar Purkinje cell outputs. Dentate nucleus stimulation (25 pulses) evoked a comparable but briefer (baseline recovery within 7 s) increase in prefrontal cortex DA efflux compared to similar cerebellar stimulation in +/+ mice. However, in Lc/+ mice 25 pulse dentate nucleus evoked prefrontal cortex DA efflux was attenuated by 60% with baseline recovery within 4 s suggesting that dentate nucleus outputs to prefrontal cortex remain partially functional. DA reuptake blockade enhanced 100 pulse stimulation evoked prefrontal cortex responses, while serotonin or norepinephrine reuptake blockade were without effect indicating the specificity of the amperometric recordings to DA. Results provide neurochemical evidence that the cerebellum can modulate DA efflux in the prefrontal cortex. Together, these findings may explain why cerebellar and frontal cortical pathologies co-occur, and may provide a mechanism that accounts for the diversity of symptoms common to multiple developmental disorders.     

Changes in neuronal activity related to the repetition and relative familiarity of visual stimuli in rhinal and adjacent cortex of the anaesthetised rat

Employing the same techniques as have been used with conscious rats, this study describes neuronal responses signalling information concerning the prior occurrence of visual stimuli in unconscious rats. Recordings of the activity of 387 neurones were made while anaesthetised rats were shown objects. Changes in neuronal responses related to stimulus repetition and the relative familiarity of visual stimuli were sought. The areas sampled were lateral occipital cortex, area TE of temporal cortex, perirhinal cortex and the hippocampal formation. The response to the first presentations of unfamiliar objects was significantly different from that to their second presentations for 30 (35%) of 86 visually responsive neurones; for 23 of the neurones was smaller when the stimulus was repeated, whereas for 7 it was larger. For all of these neurones the response change was maintained across intervening trials on which other stimuli were shown. For 4 (25%) of 16 neurones so tested, the response decrement persisted across at least 10 intervening trials. The activity of 63 neurones was recorded while rats were shown highly familiar as well as unfamiliar objects. The response to unfamiliar objects was significantly different from that to highly familiar objects for 3 (23%) of 13 visually responsive neurones. The types of neuronal response and their incidence expressed as a proportion of the number of visually responsive neurones were similar to those found in unanaesthetised rats (though the proportion of visually responsive neurones encountered in the anaesthetised rat was lower). The results indicate that information concerning the prior occurrence of stimuli is processed even under anaesthesia.     

Quantitative analysis of a vulnerable subset of pyramidal neurons in Alzheimer's disease: I. Superior frontal and inferior temporal cortex

Various cytoskeletal proteins have been implicated in the cellular pathology of Alzheimer's disease. A monoclonal antibody (SMI32) that recognizes nonphosphorylated epitopes on the medium (168 kDa) and heavy (200 kDa) subunits of neurofilament proteins has been used to label and analyze a specific subpopulation of pyramidal neurons in the prefrontal and inferior temporal cortices of normal and Alzheimer's disease brains. In Alzheimer's disease, the distribution of neuropathological markers predominates in layers III and V in these association areas. In these neocortical regions, SMI32 primarily labels the perikarya and dendrites of large pyramidal neurons, predominantly located within layers III and V. In Alzheimer's disease, a dramatic loss of SMI32-immunoreactive (ir) cells was observed, affecting particularly the largest cells (i.e., cells with a cross-sectional perikaryal area larger than 350 microns 2). The staining intensity of the largest SMI32-ir neurons was significantly reduced in Alzheimer's disease cases, suggesting that an inappropriate phosphorylation of these cytoskeletal proteins may take place in the course of the pathological process. In addition, the SMI32-ir neuron loss and total neuron loss were highly correlated with neurofibrillary tangle counts, whereas such a correlation was not observed with neuritic plaque counts. These quantitative data suggest that SMI32-ir neurons represent a small subset of pyramidal cells that share certain anatomical and molecular characteristics and are highly vulnerable in Alzheimer's disease. Other studies have suggested that SMI32-ir neurons are likely to furnish long corticocortical projections. Thus, their loss would substantially diminish the effectiveness of the distributed processing capacity of the neocortex, resulting in a neocortical isolation syndrome as reflected by the clinical symptomatology observed in these patients. Such correlations between the expression of a selective cellular pathology and specific elements of cortical circuitry will increase our understanding of the molecular and cellular characteristics underlying a given neuronal subclass vulnerability in Alzheimer's disease or other neurodegenerative disorders.     

Processing of binaural spatial information in human auditory cortex: Neuromagnetic responses to interaural timing and level differences

This study was designed to test two hypotheses about binaural hearing: (1) that binaural cues are primarily processed in the hemisphere contralateral to the perceived location of a sound; and (2) that the two main binaural cues, interaural timing differences and interaural level differences, are processed in separate channels in the auditory cortex. Magnetoencephalography was used to measure brain responses to dichotic pitches - a perception of pitch created by segregating a narrow band of noise from a wider band of noise - derived from interaural timing or level disparities. Our results show a strong modulation of interhemispheric M100 amplitudes by ITD cues. When these cues simulated source presentation unilaterally from the right hemispace, M100 amplitude changed from a predominant right hemisphere pattern to a bilateral pattern. In contrast, ILD cues lacked any capacity to alter the right hemispheric distribution. These data indicate that intrinsic hemispheric biases are large in comparison to any contralaterality biases in the auditory system. Importantly, both types of binaural cue elicited a circa 200 ms latency object-related negativity component, believed to reflect automatic cortical processes involved in distinguishing concurrent auditory objects. These results support the conclusion that ITDs and ILDs are processed by distinct neuronal populations to relatively late stages of cortical processing indexed by the M100. However information common to the two cues seems to be extracted for use in a subsequent stage of auditory scene segregation indexed by the object related negativity. This may place a new bound on the extent to which sound location cues are processed in separate channels of the auditory cortex.     

The pyramidal neuron in occipital,temporal and prefrontal cortex of the owl monkey (Aotus trivirgatus): regional specialization in cell structure

Recent studies have revealed marked regional variation in pyramidal cell morphology in primate cortex. In particular, pyramidal cells in human and macaque prefrontal cortex (PFC) are considerably more spinous than those in other cortical regions. PFC pyramidal cells in the New World marmoset monkey, however, are less spinous than those in man and macaques. Taken together, these data suggest that the pyramidal cell has become more branched and more spinous during the evolution of PFC in only some primate lineages. This specialization may be of fundamental importance in determining the cognitive styles of the different species. However, these data are preliminary, with only one New World and two Old World species having been studied. Moreover, the marmoset data were obtained from different cases. In the present study we investigated PFC pyramidal cells in another New World monkey, the owl monkey, to extend the basis for comparison. As in the New World marmoset monkey, prefrontal pyramidal cells in owl monkeys have relatively few spines. These species differences appear to reflect variation in the extent to which PFC circuitry has become specialized during evolution. Highly complex pyramidal cells in PFC appear not to have been a feature of a common prosimian ancestor, but have evolved with the dramatic expansion of PFC in some anthropoid lineages.     

N-Methyl-d-aspartate receptors regulate 5-HT release in the raphe nuclei and frontal cortex of freely moving rats: differential role of 5-HT1A autoreceptors

The effects of infusing N-methyl-

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-aspartate (NMDA) into the raphe nuclei on release of 5-HT in this brain region and also the frontal cortex of the same animal were studied using in vivo microdialysis in freely moving rats. Infusion of 25 μM NMDA into the raphe led to a substantial decrease in dialysate 5-HT in this region and a prolonged increase in terminal 5-HT release in the frontal cortex. These effects were blocked by the specific NMDA receptor antagonist 2-amino-5-phosphonopentanoic acid (D-AP5; 100 μM). When 25 μM NMDA was co-infused into the raphe with the selective 5-HT_1A receptor antagonist (N-{2-{4-(2-methoxyphenyl)-1-piperazinyl}ethyl-N-(2-pyridinyl)cyclohexanecarboxamide) (WAY-100635; 1.0 μM) the effect of NMDA infusion was unaltered. WAY-100635 infused alone into the raphe did not alter local 5-HT or extracellular 5-HT in the cortex. Infusion of 100 μM NMDA into the raphe was followed by an increase in local dialysate 5-HT and a decrease in 5-HT release in the cortex. These changes were reversed by D-AP5. Following infusion of 100 μM NMDA with 1.0 μM WAY-100635 into the raphe local 5-HT release was still increased, however, the decrease in 5-HT observed in the frontal cortex was abolished. These data suggest that the degree of NMDA receptor activation leads to dramatically different outcomes with regard to serotonergic transmission to the frontal cortex. Furthermore, there appears to be a differential role of the 5-HT_1A autoreceptor in regulating these effects. These data are discussed in relation to other studies on the regulation of serotonergic transmission in ascending pathways.     

Evidence for bilateral control of skilled movements: ipsilateral skilled forelimb reaching deficits and functional recovery in rats follow motor cortex and lateral frontal cortex lesions

Unilateral damage to cortical areas in the frontal cortex produces sensorimotor deficits on the side contralateral to the lesion. Although there are anecdotal reports of bilateral deficits after stroke in humans and in experimental animals, little is known of the effects of unilateral lesions on the same side of the body. The objective of the present study was to make a systematic examination of the motor skills of the ipsilateral forelimb after frontal cortex lesions to either the motor cortex by devascularization of the surface blood vessels (pial stroke), or to the lateral cortex by electrocoagulation of the distal branches of the middle cerebral artery (MCA stroke). Plastic processes in the intact hemisphere were documented using Golgi-Cox dendritic analysis and by intracortical microstimulation analysis. Although tests of reflexive responses in forelimb placing identified a contralateral motor impairment following both cortical lesions, quantitative and qualitative measures of skilled reaching identified a severe ipsilateral impairment from which recovery was substantial but incomplete. Golgi-impregnated pyramidal cells in the forelimb area showed an increase in dendritic length and branching. Electrophysiological mapping showed normal size forelimb representations in the lesioned rats relative to control animals. The finding of an enduring ipsilateral impairment in skilled movement is consistent with a large but more anecdotal literature in rats, nonhuman primates and humans, and suggests that plastic changes in the intact hemisphere are related to that hemisphere's contribution to skilled movement.     

Parietal,temporal, and occipita projections to cortex of the superior temporal sulcus in the rhesus monkey: A retrograde tracer study

The afferent cortical connections of individual cytoarchitectonic areas within the superior temporal sucus (STS) of the rhesus monkey were studied by retrograde tracer techniques, including double tracer experiments. Rostral superior temporal polysensory (STP) cortex (area TPO-1) receives input from the rostral superior temporal gyrus (STG), cortex of the circular sulcus, and parahippocampal gyrus (PHG) (areas 35, TF, and TL). Mid-STP cortex (areas TPO-2 and -3) has input from the mid-STG, cortex of the mid-circular sulcus, caudal inferior parietal lodule (IPL), cingulate gyrus (areas, 23, 24, retrosplenial cortex), and mid-PHG (areas 28, TF, TH, and TL). Caudal STP cortex (area TPO-4) has afferent connections with the caudal STG, cortex of the cauda insula and caudal circular sulcus, caudal IPL, lower bank of the intraparietal sulcus (IPS), medial parietal lobe, cingulate gyrus, and mid- and caudal PHG (areas TF, TH, TL; prostriate area). The most rostral cortex of the lower bank of the STS (areasTEa and TEm), a presumed visual association area, receives input from the rostal inferotemporal (IT) region; more cauda portions of areas TEa and TEm have afferent connections with the caudal IT region, PHG, preoccipital gyrus, and cortex of the lower bank of the IPS. © 1994 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Differential roles of inferior frontal and inferior parietal cortex in task switching: Evidence from stimulus‐categorization switching and response‐modality switching

We used fMRI to investigate both common and differential neural mechanisms underlying two distinct types of switching requirements, namely switching between stimulus categorizations (color vs. form) and switching between response modalities (hand vs. foot responses). Both types of switching induced similar behavioral shift costs. However, at the neural level, switching between stimulus categorizations led to left‐hemispheric activations including the inferior frontal gyrus as well as the intraparietal sulcus extending to the superior parietal gyrus and the supramarginal gyrus. In contrast, switching between response modalities was associated mainly with left‐hemispheric activation of the intraparietal sulcus and the supramarginal gyrus. A conjunction analysis indicated common activation of the left intraparietal sulcus and the supramarginal gyrus for both types of switching. Together, these results qualify previous claims about a general role of the left prefrontal cortex in task control by suggesting that the left inferior frontal gyrus is specifically involved in switching between stimulus categorizations, whereas parietal cortex is more generally implicated in the selection of action rules. Hum Brain Mapp, 2013. © 2012 Wiley Periodicals, Inc.