Human ventral parietal cortex plays a functional role on visuospatial attention and primary consciousness. A repetitive transcranial magnetic stimulation study

In this paper, we used repetitive transcranial magnetic stimulation (rTMS) in 18 normal subjects to investigate whether the ventral posterior parietal cortex (PPC) plays a causal role on visuospatial attention and primary consciousness and whether these 2 functions are linearly correlated with each other. Two distinct experimental conditions involved a similar visual stimuli recognition paradigm. In "Consciousness" experiment, number of consciously perceived visual stimuli was lower by about 10% after rTMS (300 ms, 20 Hz, motor threshold intensity) on left or right PPC than after sham (pseudo) rTMS. In "Attentional" Posner's experiment, these stimuli were always consciously perceived. Compared with sham condition, parietal rTMS slowed of about 25 ms reaction time to go stimuli, thus disclosing effects on endogenous covert spatial attention. No linear correlation was observed between the rTMS-induced impairment on attention and conscious perception. Results suggest that PPC plays a slight but significant causal role in both visuospatial attention and primary consciousness. Furthermore, these high-level cognitive functions, as modulated by parietal rTMS, do not seem to share either linear or simple relationships.     

Imaging the brain activity changes underlying impaired visuospatial judgments: simultaneous FMRI, TMS, and behavioral studies

Damage to parietal cortex impairs visuospatial judgments. However, it is currently unknown how this damage may affect or indeed be caused by functional changes in remote but interconnected brain regions. Here, we applied transcranial magnetic stimulation (TMS) to the parietal cortices during functional magnetic resonance imaging (fMRI) while participants were solving visuospatial tasks. This allowed us to observe both the behavioral and the neural effects of transient parietal activity disruption in the active healthy human brain. Our results show that right, but not left, parietal TMS impairs visuospatial judgment, induces neural activity changes in a specific right-hemispheric network of frontoparietal regions, and shows significant correlations between the induced behavioral impairment and neural activity changes in both the directly stimulated parietal and remote ipsilateral frontal brain regions. The revealed right-hemispheric neural network effect of parietal TMS represents the same brain areas that are functionally connected during the execution of visuospatial judgments. This corroborates the notion that visuospatial deficits following parietal damage are brought about by a perturbation of activity across a specific frontoparietal network, rather than the lesioned parietal site alone. Our experiments furthermore show how concurrent fMRI and magnetic brain stimulation during active task execution hold the potential to identify and visualize networks of brain areas that are functionally related to specific cognitive processes.     

Developmental changes in mental arithmetic: evidence for increased functional specialization in the left inferior parietal cortex

Arithmetic reasoning is arguably one of the most important cognitive skills a child must master. Here we examine neurodevelopmental changes in mental arithmetic. Subjects (ages 8-19 years) viewed arithmetic equations and were asked to judge whether the results were correct or incorrect. During two-operand addition or subtraction trials, for which accuracy was comparable across age, older subjects showed greater activation in the left parietal cortex, along the supramarginal gyrus and adjoining anterior intra-parietal sulcus as well as the left lateral occipital temporal cortex. These age-related changes were not associated with alterations in gray matter density, and provide novel evidence for increased functional maturation with age. By contrast, younger subjects showed greater activation in the prefrontal cortex, including the dorsolateral and ventrolateral prefrontal cortex and the anterior cingulate cortex, suggesting that they require comparatively more working memory and attentional resources to achieve similar levels of mental arithmetic performance. Younger subjects also showed greater activation of the hippocampus and dorsal basal ganglia, reflecting the greater demands placed on both declarative and procedural memory systems. Our findings provide evidence for a process of increased functional specialization of the left inferior parietal cortex in mental arithmetic, a process that is accompanied by decreased dependence on memory and attentional resources with development.     

Connection patterns distinguish 3 regions of human parietal cortex

Three regions of the macaque inferior parietal lobule and adjacent lateral intraparietal sulcus (IPS) are distinguished by the relative strengths of their connections with the superior colliculus, parahippocampal gyrus, and ventral premotor cortex. It was hypothesized that connectivity information could therefore be used to identify similar areas in the human parietal cortex using diffusion-weighted imaging and probabilistic tractography. Unusually, the subcortical routes of the 3 projections have been reported in the macaque, so it was possible to compare not only the terminations of connections but also their course. The medial IPS had the highest probability of connection with the superior colliculus. The projection pathway resembled that connecting parietal cortex and superior colliculus in the macaque. The posterior angular gyrus and the adjacent superior occipital gyrus had a high probability of connection with the parahippocampal gyrus. The projection pathway resembled the macaque inferior longitudinal fascicle, which connects these areas. The ventral premotor cortex had a high probability of connection with the supramarginal gyrus and anterior IPS. The connection was mediated by the third branch of the superior longitudinal fascicle, which interconnects similar regions in the macaque. Human parietal areas have anatomical connections resembling those of functionally related macaque parietal areas.     

Color discrimination involves ventral and dorsal stream visual areas

We used positron emission tomography (PET) and functional magnetic resonance imaging (fMRI) in human subjects to investigate whether the ventral and dorsal visual stream cooperate when active judgements about color have to be made. Color was used as the attribute, because it is processed primarily in the ventral stream. The centrally positioned stimuli were equiluminant shades of brown. The successive color discrimination task was contrasted to a dimming detection task, in which retinal input was identical but with double the number of motor responses. The stimulus presentation rate was parametrically varied and a constant performance level was obtained for all conditions. The visual activation sites were identified by retinotopic mapping and cortical flattening. In addition, one psychophysical and two fMRI experiments were performed to control for differences in visuospatial attention and motor output. Successive color discrimination involved early visual areas, including V1 and VP and the ventral color-responsive region, as well as anterior and middle dorsal intraparietal sulcus, dorsal premotor cortex and pre-SMA. Cortical regions involved in dimming detection and motor output included area V3A, hMT/V5+, lateral occipital sulcus, posterior dorsal intraparietal sulcus, primary motor cortex and SMA. These experiments demonstrated that even with color as the attribute, successive discrimination, in which a decision process has to link visual signals to motor responses, involves both ventral and dorsal visual stream areas.     

Anatomy of the parietal lobe: Mapping the individual pattern

Summary Using magnetic resonance imaging with planes of section tangential to the left or right perietal convexity, we studied the sulcus pattern of the parietal lobes in 50 healthy subjects. The postcentral sulcus and the intraparietal sulcus were easily identified. As a characteristic landmark, and corresponding to postmortem findings, both sulci joined in 77% of the 100 hemispheres. The presurgical recognition of individual parietal lobe anatomy may improve surgical planning, in particular with an intended persulcal approach.     

Priming frequencies of transcranial magnetic stimulation over Wernicke's area modulate word detection

Priming stimulations have shown powerful effects on motor cortex behavior. However, the effects over language areas have not been explored. We assessed the effects of different priming frequencies of repetitive transcranial magnetic stimulation (rTMS), 1 Hz rTMS or 50 Hz bursts of rTMS (theta burst stimulation [TBS]), on temporoparietal language areas (i.e., Wernicke's area) localized with functional magnetic resonance imaging. Functional maps were acquired during an auditory word-detection task with native or foreign language sentences in 14 healthy men. Frameless stereotaxy was used to guide the transcranial magnetic stimulation coil position over Wernicke's area. Active and placebo randomized sessions of priming stimulations (1 Hz rTMS or TBS) were applied at rest, and response times (RTs) were recorded during the auditory word-detection task performed subsequently with 1 Hz rTMS. Individual anatomofunctional maps localized activation in Wernicke's area. Repeated-measure analysis of variance for RTs revealed that priming with 1 Hz rTMS facilitated the detection of native words, whereas priming with TBS facilitated the detection of foreign words. Consistent with motor cortex studies, these findings suggest that priming frequency plays a crucial role in word detection in the auditory stream.     

Modification of practice-dependent plasticity in human motor cortex by neuromodulators

Practice-dependent plasticity underlies motor learning in everyday life and motor relearning after lesions of the nervous system. Previous studies showed that practice-dependent plasticity is modifiable by neuromodulating transmitters such as norepinephrine (NE), dopamine (DA) or acetylcholine (ACh). Here we explored, for the first time comprehensively and systematically, the modifying effects of an agonist versus antagonist in each of these neuromodulating transmitter systems on practice-dependent plasticity in healthy subjects in a placebo-controlled, randomized, double-blind crossover design. We found that the agonists in all three neuromodulating transmitter systems (NE: methylphenidate; DA: cabergoline; ACh: tacrine) enhanced practice-dependent plasticity, whereas the antagonists decreased it (NE: prazosin; DA: haloperidol; ACh: biperiden). Enhancement of plasticity under methylphenidate and tacrine was associated with an increase in corticomotoneuronal excitability of the prime mover of the practice, as measured by the motor evoked potential amplitude, but with a decrease under cabergoline. Our findings demonstrate that agonists and antagonists in various neuromodulating transmitter systems produce significant and oppositely directed modifications of practice-dependent plasticity in human motor cortex. Enhancement of plasticity occurred through different strategies that either favoured extrinsic (NE, ACh) or intrinsic (DA) modulating influence on the motor cortical output network.     

Prefrontal cortex asymmetry for memory encoding of words and abstract shapes

Previous work suggested a differential contribution of prefrontal cortex (PFC) to successful encoding depending on the stimulus material. Here, we tested the hypothesis that encoding of words preferentially involves the left PFC, while encoding of nonverbal items (abstract shapes) relies on the right PFC. We used an experimental design that evaluated encoding of both words and abstract shapes in the same healthy volunteers. A transient virtual lesion of the left or the right PFC was elicited with transcranial magnetic stimulation (TMS) while subjects memorized verbal and nonverbal items. We found that encoding of verbal material was disrupted by left PFC stimulation, whereas encoding of nonverbal material was disrupted by right PFC stimulation. These results demonstrate a functionally relevant lateralization of prefrontal contribution for verbal and nonverbal memory encoding.     

Role of the superior temporal region in human visual motion perception

While moving objects are usually seen using luminance (first-order) cues, humans can perceive the motion of objects via non-luminance (second-order) cues. Contrary to previous case reports, no physiological studies have elucidated distinct differences in the cortical regions involved in first- and second-order motion processes. We investigated brain responses related to these two types of motion perception in human subjects using 3 T functional magnetic resonance imaging and strictly controlled apparent motion stimulus pairs. Comparison of brain activation to moving versus static states of each motion stimulus isolated cortical activity related to each type of motion perception. We found a selective neural response to second-order motion stimulus in the anterior part of the superior temporal sulcus (STS) contralateral to stimulus presentation and cue-invariant activation of MT/V5+. No significant activation in the STS was observed by the first-order motion, even when its visibility was reduced to levels comparable to that of second-order motion. Furthermore, the STS demonstrated significant activation for highly visible motion stimulus with both first- and second-order attributes. The STS represents the cardinal structure for perception of second-order motions, although further studies are needed to elucidate the exact neural process occurring in this area.     

Suppressing versus releasing a habit: frequency-dependent effects of prefrontal transcranial magnetic stimulation

When subjects are required to generate a random sequence of numbers they typically produce too many forward and backward 'counts' (e.g. 5-6, 4-3). This counting bias is interpreted as the consequence of an interference by overlearned tendencies to arrange numbers according to their natural order. Inhibition of such well-learned routines is known to rely on frontal lobe functioning. We examined differential effects of slow (1 Hz) and fast (10 Hz) repetitive transcranial magnetic stimulation (rTMS) over the left or right dorsolateral prefrontal cortex (DLPFC) on random number generation (RNG) performance. Eighteen healthy men performed an RNG task. Those subjects stimulated over the left DLPFC showed a frequency-dependent rTMS effect: counting bias was significantly reduced after the 1 Hz stimulation compared with baseline, but significantly exaggerated after the 10 Hz stimulation compared with 1 Hz stimulation. In contrast, the sequences of the subjects stimulated over the right DLPFC showed the well-known excess of counting in all conditions (i.e. baseline, 1 Hz and 10 Hz). These findings confirm the functional importance of specifically the left DLPFC in sequential response production and show, for the first time, that rTMS affects cognitive processing in a frequency-dependent manner.     

Repetitive transcranial magnetic stimulation effects on brain function and cognition among elders with memory dysfunction. A randomized sham-controlled study

In the present study, we aimed to investigate the effects of repetitive transcranial magnetic stimulation (rTMS) on memory performance and brain activity in elders presenting with subjective memory complaints and a memory performance within the low normal range. Forty participants underwent 2 functional magnetic resonance imaging (fMRI) sessions, in which they were administered 2 equivalent face-name memory tasks. Following each fMRI, subjects were asked to pair faces with their corresponding proper name. In-between, high-frequency rTMS was applied randomly using real or sham stimulation in a double-blind design. Only subjects who received active rTMS improved in associative memory significantly. This was accompanied by additional recruitment of right prefrontal and bilaterial posterior cortical regions at the second fMRI session, relative to baseline scanning. Our findings reflect a potentiality of rTMS to recruit compensatory networks, which participate during the memory-encoding process. Present results represent the first evidence that rTMS is capable of transitorily and positively influencing brain function and cognition among elders with memory complaints.     

Magnetic Resonance Imaging Data in the Evaluation of Effects of Functional Electrical Stimulation on Knee Joints of Adolescents with Spinal Cord Injury

Abstract

Diagnostic imaging, consisting of roentgenograms and magnetic resonance images (MRIs), was performed as part of an evaluation of the effects of a functional electrical stimulation (FES) program on the knee joints of 29 adolescents with spinal cord injuries following implantation of fine-wire intramuscular electrodes in their lower extremity muscles. The subjects underwent a regimen consisting of stimulated exercise, standing and/or walking. The effects of FES on knee joints were prospectively studied by reviewing diagnostic imaging data. Evaluation of MRIs and plain radiographs showed no evidence of knee joint pathology secondary to FES exercise or weight bearing. In fact, based on follow-up of MRI scan, many of the joints improved following participation in the program. The MRI data supported the clinical examination of the knee joints of these children. Clinical examination appears adequate for screening for potential knee joint problems.     

Cortical mechanisms for shifting and holding visuospatial attention

Access to visual awareness is often determined by covert, voluntary deployments of visual attention. Voluntary orienting without eye movements requires decoupling attention from the locus of fixation, a shift to the desired location, and maintenance of attention at that location. We used event-related functional magnetic resonance imaging to dissociate these components while observers shifted attention among 3 streams of letters and digits, one located at fixation and 2 in the periphery. Compared with holding attention at the current location, shifting attention between the peripheral locations was associated with transient increases in neural activity in the superior parietal lobule (SPL) and frontal eye fields (FEF), as in previous studies. The supplementary eye fields and separate portions of SPL and FEF were more active for decoupling attention from fixation than for shifting attention to a new location. Large segments of precentral sulcus (PreCS) and posterior parietal cortex (PPC) were more active when attention was maintained in the periphery than when it was maintained at fixation. We conclude that distinct subcomponents of the dorsal frontoparietal network initiate redeployments of covert attention to new locations and disengage attention from fixation, while sustained activity in lateral regions of PPC and PreCS represents sustained states of peripheral attention.     

不同剂量芬太尼对疼痛激活脑区的影响:功能性磁共振成像研究

目的 应用功能性磁共振成像技术,评价不同剂量芬太尼对疼痛激活脑区的影响.方法 选取右利手男性健康志愿者20名,年龄20～40岁,采用随机数字表法,将受试者随机分为2组(n=10):芬太尼1.0 μg/kg组(F1组)和芬太尼1.5 μg/kg组(F2组).300 g von Frey纤维丝刺激受试者左足心作为机械性伤害性刺激.静脉注射各组相应剂量芬太尼.于给药前、给药后5、10、15、20 min时给予机械性伤害性刺激,记录VAS评分.1周后行功能性磁共振成像扫描.扫描序列包括结构像扫描和功能像扫描,其中功能像扫描包括机械性伤害性刺激P1扫描、不同剂量芬太尼的药物扫描(扫描前单次静脉注射芬太尼)和机械性伤害性刺激P2扫描.P1、P2扫描包括10 s的初始采集信号扫描及静息态(20 s)与刺激态(20 s)交替循环6次扫描.给药扫描包括空白平衡扫描4 min和给药后扫描8 min.记录芬太尼给药前后疼痛激活脑区的改变.结果 F1组(P2-P1)激活的脑区:同侧扣带回;F2组(P2 -P1)激活的脑区:双侧扣带回和对侧岛叶.F2组与F1组功能磁共振成像叠加相比(F2组-F1组)可见同侧扣带回激活.结论 机械性伤害性刺激时芬太尼可促进扣带回和岛叶的活动,且与剂量有关,提示这两个脑区可能是芬太尼发挥镇痛作用的靶位.     

Disturbing visual working memory: electrophysiological evidence for a role of the prefrontal cortex in recovery from interference

Single cell recordings in monkeys support the notion that the lateral prefrontal cortex (PFC) controls reactivation of visual working memory representations when rehearsal is disrupted. In contrast, recent fMRI findings yielded a double dissociation for PFC and the medial temporal lobe (MTL) in a letter working memory task. PFC was engaged in interference protection during reactivation while MTL was prominently involved in the retrieval of the letter representations. We present event-related potential data (ERP) that support PFC involvement in the top-down control of reactivation during a visual working memory task with endogenously triggered recovery after visual interference. A differentiating view is proposed for the role of PFC in working memory with respect to endogenous/exogenous control and to stimulus type. General implications for binding and retention mechanisms are discussed.     

正常男女性兴奋的磁共振功能成像研究

目的:利用磁共振功能成像技术探讨在色情录像刺激下正常男女性兴奋在中枢神经系统的差异。方法:健康男性和女性各20例,均为右利手,无性功能障碍史,无任何精神、心理及其他器质性疾病史。用色情录像和非色情录像刺激,每个录像片段60s,每个色情和非色情录像片段之间间隔12s。用GE1.5THD磁共振扫描系统进行血氧水平依赖的功能磁共振扫描,共扫描7.0min。用3DSPGR-T1WI序列进行全脑轴位扫描作为全脑解剖图。结果:在视听相关的性刺激下,男女激活不同的脑区:①女性双侧杏仁核激活,左侧激活体积为(220.52±17.09)mm3,右侧为(155.45±18.34)mm3,左侧明显大于右侧(P<0.05)。而男性仅左侧杏仁核被激活。②正常男性左前扣带回的激活较女性明显,男性左前扣带回激活体积为(420.75±19.37)mm3,女性为(310.67±10.53)mm3,两者差异有显著性(P<0.05);③女性胼胝体压部激活较男性明显(P<0.01),女性激活体积为(473.45±14.92)mm3,男性为(363.32±13.30)mm3。结论:男女性反应在中枢神经系统的激活存在差异,推测男女性脑结构和功能存在不同是这种差异的基础。     

Acupuncture using laser needles modulates brain function: first evidence from functional transcranial Doppler sonography and functional magnetic resonance imaging

Acupuncture using laser needles is a new totally painless stimulation method which has been described for the first time. This paper presents an experimental double-blind study in acupuncture research in healthy volunteers using a new optical stimulation method. We investigated 18 healthy volunteers (mean age±SD: 25.4±4.3 years; range: 21–30 years; 11 female, 7 male) in a randomized controlled cross-over trial using functional multidirectional transcranial ultrasound Doppler sonography (fTCD; n=17) and performed functional magnetic resonance imaging (fMRI) in one volunteer. Stimulation of vision-related acupoints resulted in an increase of mean blood flow velocity in the posterior cerebral artery measured by fTCD [before stimulation (mean±SE): 42.2±2.5; during stimulation: 44.2±2.6; after stimulation: 42.3±2.4 cm/s, n.s.]. Mean blood flow velocity in the middle cerebral artery decreased insignificantly. Significant changes (p<0.05) of brain activity were demonstrated in the occipital and frontal gyrus by fMRI. Optical stimulation using properly adjusted laser needles has the advantage that the stimulation cannot be felt by the patient (painless and no tactile stimulation) and the operator may also be unaware of whether the stimulation system is active. Therefore true double-blind studies in acupuncture research can be performed.     

The effect of visual experience on the development of functional architecture in hMT+

We investigated whether the visual hMT+ cortex plays a role in supramodal representation of sensory flow, not mediated by visual mental imagery. We used functional magnetic resonance imaging to measure neural activity in sighted and congenitally blind individuals during passive perception of optic and tactile flows. Visual motion-responsive cortex, including hMT+, was identified in the lateral occipital and inferior temporal cortices of the sighted subjects by response to optic flow. Tactile flow perception in sighted subjects activated the more anterior part of these cortical regions but deactivated the more posterior part. By contrast, perception of tactile flow in blind subjects activated the full extent, including the more posterior part. These results demonstrate that activation of hMT+ and surrounding cortex by tactile flow is not mediated by visual mental imagery and that the functional organization of hMT+ can develop to subserve tactile flow perception in the absence of any visual experience. Moreover, visual experience leads to a segregation of the motion-responsive occipitotemporal cortex into an anterior subregion involved in the representation of both optic and tactile flows and a posterior subregion that processes optic flow only.