Laterality effects in selective attention to threat after repetitive transcranial magnetic stimulation at the prefrontal cortex in female subjects

Recently, several experiments have indicated that the left and right prefrontal cortex (PFC) are differently involved in emotional processing. The aim of this study was to investigate the role of the left and right PFC in selective attention to angry faces by using a pictorial emotional Stroop task. Slow repetitive transcranial magnetic stimulation (rTMS) was applied to the left and right PFC of 10 female subjects for 15 min on separate days. Results showed a significant effect of stimulation position: right PFC rTMS resulted in selective attention towards angry faces, whereas left PFC rTMS resulted in selective attention away from angry faces. This finding is in accordance with theoretical accounts of the neural implementation of approach and withdrawal systems.     

On the role of posterior parietal and prefrontal cortex in visuo-spatial perception and attention

Summary Monkeys with bilateral removal of caudal prefrontal cortex (area 8) or dorso-lateral parietal cortex (areas 5 and 7) or the inferior temporal cortex (area TE) were presented with two versions of a go-left/go-right visuo-spatial discrimination. In the first task they had to displace either the left or right of two identical plaques according to whether both plaques were black or white respectively. There were no performance differences among groups. In the second task, the two plaques were always red and the appropriate response was indicated by whether a spatially remote third plaque was black or white. Both the prefrontal and parietal groups were impaired relative to the inferotemporal group on this task. The results indicate that whether an impairment occurs on a task that is thought to test the perception of egocentric space may depend on whether the animal has to notice and attend to a remote cue, and that an attentional disorder may also explain impairments reported on tests of allocentric perception where the critical cue is spatially remote from the response site.     

Influences of lesions of parietal cortex on visual spatial attention in humans

Summary Several brain areas have been identified with attention, because damage to these regions leads to neglect and extinction. We have tested elements of visual attentional processing in patients with parietal, frontal, or temporal lesions and compared their responses to control subjects. Normal humans respond faster in a reaction time task when the spatial location of a target is correctly predicted by an antecedent stimulus (valid cue) than when the location is incorrectly predicted (invalid cue). The cue is hypothesized to shift attention towards its location and thereby facilitate or impede response latencies. The reaction times of individuals with damage to the parietal lobe are somewhat slowed for targets ipsilateral or contralateral to the side of the lesion if the targets are preceded by valid cues. These same patients are extremely slow in responding to targets in the visual field contralateral to the lesion when the cue has just appeared in the unaffected (ipsilateral) visual field. In addition, these individuals are especially slow in responding to targets in either visual field when the lights are preceded by weak, diffuse illumination of the entire visual field. Patients with lesions of the frontal lobe have very slow reaction times in general and, as is the case for patients with lesions of the temporal lobe, are slow in all conditions for targets in the field contralateral to the lesion. These patterns are probably not associated with attentional defects. For patients with parietal lesions, these studies demonstrate a further deficit in a cued reaction-time task suggesting abnormal visual attention. Since different sites of brain damage yield different patterns of responses, tests such as these could be of analytic and diagnostic value.     

Event-related brain potential and heart rate manifestations of visual selective attention

Twenty-eight volunteers were instructed to attend stimuli presented at one side of the computer screen and to ignore stimuli presented at the other side. Both attended and unattended stimulus series consisted of targets (25%) and nontargets (75%) defined on the basis of stimulus shape. Attended targets required a binary choice based on stimulus color. Selective attention led to the expected increase in both midlatency (N2b) and late (P3) brain potential components. Furthermore, selective attention led to increased anticipatory cardiac slowing preceding the target stimulus and to increased primary bradycardia. Correlational analyses revealed a positive relation between the effects of selective attention on N2b amplitude and primary bradycardia suggestive of cortical involvement in the chronotropic control of heart rate.     

跨颅磁刺激观察前额叶皮层在学习记忆中的作用

目的为了探讨前额叶皮层的功能。方法在被试进行联合搜索作业(conjunction search task)时,使用跨颅磁刺激干扰被试者右侧前额叶皮层的活动,观察被试者在训练前后反应时间的变化。结果发现磁刺激干扰前额叶的活动,明显地延长了被试者在训练前的反应时间,对训练之后的反应时间几乎没有变化。结论这说明右侧前额叶参与了记忆的编码,对记忆的提取没有作用。     

Prefrontal cortex of the cat: Paucity of afferent projections from the parietal cortex

Summary Twenty-one cat brains with cortical injections of horseradish peroxidase resulting in labelled cells in the thalamic mediodorsal nucleus (MD) were screened for afferent projections from the parietal cortex. Contrary to expectation, nearly the whole prefrontal cortex (PFC) situated around the frontal pole was free of parietal afferents, while a small area in the anterior sylvian gyrus (orbito-insular subregion of PFC) consistently received afferents from the parietal cortex. The few afferents projecting to the cortex around the frontal pole originated exclusively from the convexity of the suprasylvian gyrus, while the great majority of the parietal neurons projecting to the anterior sylvian gyrus was situated within the fundus of the suprasylvian sulcus. While the main regions of the prefrontal cortex of the rhesus monkey receive a substantial projection from the parietal lobe, whereas the main regions of the cat's prefrontal cortex are free of afferents from the parietal cortex, possible differences in the parieto-prefrontal organization of both species are discussed. Furthermore, differences between the orbito-insular subregion and the rest of the PFC are emphasized.This study was carried out mainly at the University of Konstanz.Dr. B. Petrovi-Mini was a visiting scientist at the University of Konstanz. Research was supported in part by grant Ma 795 from the Deutsche Forschungsgemeinschaft (DFG)     

Effects of repetitive transcranial magnetic stimulation over dorsolateral prefrontal and posterior parietal cortex on memory-guided saccades

We investigated the role of the dorsolateral prefrontal cortex (DLPFC) and the posterior parietal cortex (PPC) in a visuospatial delayed-response task in humans. Repetitive transcranial magnetic stimulation (20 Hz, 0.5 s) was used to interfere temporarily with cortical activity in the DLPFC and PPC during the delay period. Omnidirectional memory-guided saccades with a 3-s delay were used as a quantifiable motor response to a visuospatial cue. The question addressed was whether repetitive transcranial magnetic stimulation (rTMS) over the DLPFC or PPC during the sensory of memory phase affects accuracy of memory-guided saccades. Stimulation over the primary motor cortex served as control. Stimulation over the DLPFC significantly impaired accuracy of memory-guided saccades in amplitude and direction. Stimulation over the PPC impaired accuracy of memory-guided saccades only when applied within the sensory phase (50 ms after cue offset), but not during the memory phase (500 ms after cue offset). These results provide further evidence for a parieto-frontal network controlling performance of visuospatial delayed-response tasks in humans. It can be concluded that within this network the DLPFC is mainly concerned with the mnemonic respresentation and the PPC with the sensory representation of spatially defined perceptual information. Received: 22 April 1996/Accepted: 16 June 1997     

Inter-individual differences in the polarity of early visual responses and attention effects

While there is a general agreement about the sensory properties of the early-latency C1 (P/N80) and P1 components of visual evoked potentials (VEPs), the literature is not consistent about the timing of modulatory attention effects at an early sensory stage for either space- or object-based stimulus features. The aim of this study was to investigate whether inter-individual differences in VEP morphology might affect the nature and polarity of amplitude changes via selective visual attention. EEG was recorded in 20 right-handed individuals while they viewed drawings of familiar objects presented slightly lateralized and performed a categorization task. It consisted in paying attention and responding to a conjunction of space and object features. On the basis of VEP morphology, and independently of task factors, subjects were subdivided in two groups: one group exhibited a prominent N80 and the other a prominent P80 in the same latency range from the same electrode sites. RTs to targets were identical in the two groups, suggesting that morphology was independent of task-related factors. VEP morphology affected the direction and amplitude of spatial and non-spatial attention effects. While attention effects always resulted in increased positivity for the P80 group (at both the C1 and P1 levels), shape relevance was associated with enhanced N80 and P1 responses in the N80 group. These data provide evidence for an inversion of attention effects, in addition to inversion of C1 polarity, in people exhibiting negative C1 at mesial occipital sites.     

Segregation of working memory functions within the dorsolateral prefrontal cortex

It is now widely accepted that the prefrontal cortex (PFC) plays a critical role in the neural network subserving working memory (WM). At least three related questions are still under debate: (1) is the PFC critical for all constituent processes of WM (i.e., short-term storage, manipulation, and utilization of mental representations) or only in one or a few of them? (2) Is there segregation of function among different cytoarchitectonic subdivisions of the PFC? (3) If this be the case, is this segregation based on the nature of the information being processed or on the type of cognitive operation performed? The present review article describes findings in the monkey supporting a modular "domain-specific" model of PFC functional organization with respect to WM operations. In this model, the dorsolateral prefrontal cortex (DLPFC) is composed of several subregions, based primarily on the nature of the information being processed in WM. Storage and processing functions are integrally related in each area. Future studies designed to map as yet uncharted areas of prefrontal cortex with refined anatomical and physiological approaches may provide a critical test of the model and evaluate the extent to which it applies generally or, instead, mainly to visual domains or only to dorsolateral convexity areas.     

Topography of commissural fibers of the prefrontal cortex in the rhesus monkey

Summary The topography of commissural fibers of the prefrontal cortex was studied in the rhesus monkey using autoradiography. Commissural fibers originating in the medial prefrontal and the caudal orbital regions course through the anterior portion of the genu and the rostrum of the corpus callosum, while those from the arcuate concavity travel at the rostral border of the body of the corpus callosum. Fibers emanating from the peri-principalis region occupy an intermediate position in the genu of the corpus callosum.     

Relationship between trait anxiety, prefrontal cortex, and attention bias to angry faces in children and adolescents

Using event-related functional magnetic resonance imaging (fMRI) with a visual-probe task that assesses attention to threat, we investigated the cognitive and neurophysiological correlates of trait anxiety in youth. During fMRI acquisition, 16 healthy children and adolescents viewed angry-neutral face pairs and responded to a probe that was on the same (angry-congruent) or opposite (angry-incongruent) side as the angry face. Attention bias scores were calculated by subtracting participants' mean reaction time for angry-congruent trials from angry-incongruent trials. Trait anxiety was positively associated with attention bias towards angry faces. Neurophysiologically, trait anxiety was positively associated with right dorsolateral prefrontal cortex (PFC) activation on a contrast of trials that reflect the attention bias for angry faces (i.e. angry-incongruent versus angry-congruent trials). Trait anxiety was also positively associated with right ventrolateral PFC activation on trials with face stimuli (vesus baseline), irrespective of their emotional content.     

Spatio-temporal integration in the substrate for self-stimulation of the prefrontal cortex

The number of stimulation pulses required to maintain a half maximal rate of self-stimulation of the prefrontal cortex (PFC) was determined for various currents. Over a restricted range, the effects of decreasing the stimulation frequency could be compensated for by increasing the current. This finding cannot easily be reconciled with the hypothesis that the rewarding impact of PFC stimulation is unaffected by increments in current. The minimum current that would support self-stimulation of the PFC at high frequencies was larger than has been reported at medial forebrain bundle sites.     

Dorsolateral prefrontal cortex stimulation modulates electrocortical measures of visual attention: evidence from direct bilateral epidural cortical stimulation in treatment-resistant mood disorder

Electrocortical activity is increasingly being used to study emotion regulation and the impact of cognitive control on neural response to visual stimuli. In the current study, we used direct epidural cortical stimulation (EpCS) to examine regional specificity of PFC stimulation on the parietally-maximal late positive potential (LPP), an event-related potential (ERP) biomarker of visual attention to salient stimuli. Five patients with treatment-resistant mood disorders were stereotactically implanted with stimulating paddles over frontopolar (FP) and dorsolateral (DL) prefrontal cortex bilaterally. On their first day of activation, patients underwent sham-controlled EpCS coupled with 64-channel electroencephalograph (EEG) recordings and passive viewing of aversive and neutral images. In addition to sham, patients had either FP or DL prefrontal cortex stimulated at 2 or 4 V while they viewed neutral and aversive pictures. As expected during the sham condition, LPP was larger for aversive compared to neutral stimuli (F(1,4)=232.07, P<.001). Stimulation of DL compared to FP prefrontal cortex resulted in a reduction of the LPP (F(1,4)=8.15, P=.048). These data provide additional and unique support to the role of the DL prefrontal cortex in regulating measures of neural activity that have been linked to emotional arousal and attention. Future studies with EpCS can help directly map out various prefrontal functions in treatment-resistant mood disorder.     

Functional compensation in the lateral suprasylvian visual area following bilateral visual cortex damage in kittens

Summary Previous studies have shown that functional compensation is present in the cat's posteromedial lateral suprasylvian (PMLS) area of cortex after damage to areas 17, 18, and 19 (visual cortex) early in life but not after damage in adults. These studies all have investigated animals with a unilateral visual cortex lesion, whereas all behavioral studies of compensation for early visual cortex damage have investigated animals with a bilateral lesion. In the present experiment, we investigated whether functional compensation also is present in PMLS cortex after a bilateral visual cortex lesion early in life. We recorded from single neurons in the PMLS cortex of adult cats that had received a bilateral lesion of areas 17, 18, and 19 on the day of birth or at 8 weeks of age. We found that PMLS cells in both groups of cats had functional compensation (normal direction selectivity and ocular dominance) similar to that seen after a unilateral lesion at the same ages. These results are consistent with the hypothesis that PMLS cortex is involved in the behavioral compensation seen after early visual cortex damage. In addition, the results indicate that inputs from contralateral visual cortex are not necessary for the development of functional compensation seen in PMLS cortex.     

Delayed alternation behavior following ablations of the medial or dorsal prefrontal cortex in dogs

Medial, but nor dorsal, prefrontal ablations interfered with retention in a spatial delayed alternation task. In this problem, normal dogs showed systematic bodily orientations during the delays. It has been found previously that dorsal, but not medial, lesions produced deficits in other delayed response type tasks in which positional mediations were not used. Occurrence of impairment after a given lesion appeared to be related to whether or not the animal adopted a positional strategy for solving the task. It was suggested that the medial prefrontal cortex subserves responding to kinesthetic cues, while the dorsal cortex may have a function in behavior based on retained spatial stimuli. Comparisons were made between properties of prefrontal cortices in dog and monkey.     

Projections from inferior temporal cortex to prefrontal cortex via the uncinate fascicle in rhesus monkeys

Summary In five rhesus monkeys (Macaca, mulatta) we used anterograde and retrograde tracing techniques to investigate the projection from the inferior temporal cortex (area TE) to the prefrontal cortex as well as the course of the projecting fibers. The results showed that TE projects to both the inferior convexity and orbital surface of prefrontal cortex and that these projections course almost exclusively via the uncinate fascicle. Transection of the uncinate fascicle deprives the prefrontal cortex of virtually all input from TE, but leaves intact inputs from prestriate and parietal visual areas as well as the amygdala. Such transection also leaves intact many projections from TE to targets other than the prefrontal cortex, including the amygdala, ventral putamen, tail of the caudate nucleus, and pulvinar.     

Subcortical afferents to the prefrontal cortex in rabbits

Summary The origins of cells projecting to the prefrontal cortex of the rabbit were studied, using horseradish peroxidase (HRP) technique. HRP injected into the prefrontal cortex labeled cells in the basal forebrain, lateral hypothalamus, raphe nuclei and locus coeruleus area on both sides. Labeled cells appeared also in the nucleus medialis dorsalis of the thalamus and other thalamic nuclei on the injection side.     

Neural representation of response category and motor parameters in monkey prefrontal cortex

Conditional motor behavior, in which the relationship between stimuli and responses changes arbitrarily, is an important component of cognitive motor function in primates. It is still unclear how cognitive processing for conditional motor control determines movement parameters to directly specify motor output. To address this issue, we studied the neuronal representation of motor variables relating to conditional motor control and also directly to the metrics of motor output in prefrontal cortex (PFC). Monkeys were required to generate a force that fell within one of two categories (small and large). We found that most PFC neurons were activated as a function of force category, suggesting a role in conditional motor control. At the same time, we found that activity in many PFC neurons varied continuously with the force that was eventually produced, suggesting they participated in specifying the metrics of movements as they were executed. The results suggest that the PFC neural population encodes both what motor response should be performed and how the selected movement should be realized immediately after the visual instruction.     

Functional recovery after serial ablation of prefrontal cortex in the rat

In two experiments, adult rats with 1-stage or 2-stage ablation of discrete subfields of the prefrontal cortex were compared on spatial delayed alternation, one way active avoidance, food hoarding, ingestive behavior, and postoperative body weight. Single stage removal of the ventrolateral (sulcal or orbital) cortex produced aphagia and adipsia for several days postoperatively and a chronic reduction in body weight. Serial removal of this same cortex produced a milder effect on postoperative food and water intake, and there was no chronic reduction of body weight. Ablation of dorsomedial cortex either in one or two stages did not significantly reduce food or water intake or body weight. In contrast, single stage removal of dorsomedial cortex produced dramatic impairment on spatial delayed alternation, active avoidance, and food hoarding; whereas ventrolateral lesions either in one or two stages did not significantly affect performance on these tasks. Animals with dorsomedial lesions produced in two stages were not significantly impaired on delayed alternation or active avoidance, but on food hoarding they were just as impaired as the animals with comparable lesions induced in a single stage. It is apparent that removal of either dorsomedial or ventrolateral prefrontal cortex in two stages causes an amelioration of the deficit that is obtained with single stage destruction of these areas on some tasks, but sparing of function is not an invariant consequence of serial destruction of rat prefrontal cortex.     

The substrates for self-stimulation of the lateral hypothalamus and medial prefrontal cortex: a comparison of strength-duration characteristics

The directly activated substrates for self-stimulation of the lateral hypothalamus (LH) and medial prefrontal cortex (MPFC) were described by comparing their strength-duration characteristics. The current required to maintain a half-maximal rate of lever pressing was traded off against the pulse duration while all other stimulation parameters were kept constant. In this manner, cathodal strength-duration curves were obtained at four LH and eight MPFC sites; anodal curves were obtained at two of the LH and six of the MPFC sites. In general, the cathodal LH curves had lower rheobases than the cathodal MPFC curves and continued to descend after the MPFC curves had levelled off. At short pulse durations, the anodal curves lay above the cathodal curves, a finding more pronounced in the LH data. The two sets of curves converged at the longer pulse durations. The differences in the strength-duration curves are consistent with the notion that different directly stimulated neurons are responsible for the rewarding effects of LH and MPFC stimulation. Anatomical and physiological properties that could account for these differences are discussed.