Cerebral bases of subliminal and supraliminal priming during reading

Several studies have investigated the neural correlates of conscious perception by contrasting functional magnetic resonance imaging (fMRI) activation to conscious and nonconscious visual stimuli. The results often reveal an amplification of posterior occipito-temporal activation and its extension into a parieto-frontal network. However, some of these effects might be due to a greater deployment of attentional or strategical processes in the conscious condition. Here, we examined the brain activity evoked by visible and invisible stimuli, both of which were irrelevant to the task. We collected fMRI data in a masking paradigm in which subliminal versus supraliminal letter strings were presented as primes while subjects focused attention on another subsequent, highly visible target word. Under those conditions, prime visibility was associated with greater activity confined to bilateral posterior occipito-temporal cortices, without extension into frontal and parietal cortices. However, supraliminal primes, compared with subliminal primes, evoked more extensive repetition suppression in a widely distributed set of parieto-frontal areas. Furthermore, only supraliminal primes caused phonological repetition enhancement in left inferior frontal and anterior insular cortex. Those results suggest a 2-stage view of conscious access: Relative to masked stimuli, unmasked stimuli elicit increased occipito-temporal activity, thus allowing them to compete for global conscious access and to induce priming in multiple distant areas. In the absence of attention, however, their access to a second stage of distributed parieto-frontal processing may remain blocked.     

Attention to simultaneous unrelated auditory and visual events: behavioral and neural correlates

The cognitive and neural bases of the ability to focus attention on information in one sensory modality while ignoring information in another remain poorly understood. We hypothesized that bimodal selective attention results from increased activity in corresponding sensory cortices with a suppression of activity in non-corresponding sensory cortices. In a functional magnetic resonance imaging (fMRI) study, we presented melodies and shapes alone (unimodal) or simultaneously (bimodal). Subjects monitored for changes in an attended modality while ignoring the other. Subsequently, memory for both attended and unattended stimuli was tested. Subjects remembered attended stimuli equally well in unimodal and bimodal conditions, and significantly better than ignored stimuli in bimodal conditions. When a subject focused on a stimulus, the blood-oxygen-level-dependent (BOLD) response increased in sensory cortices corresponding to that modality in both unimodal and bimodal conditions. Additionally, the BOLD response decreased in sensory cortices corresponding to the non-presented modality in unimodal conditions and the unattended modality in bimodal conditions. We conclude that top-down attentional effects modulate the interaction of sensory cortical areas by gating sensory input. This interaction between sensory cortices enhances processing of one modality at the expense of the other during selective attention, and subsequently affects memory encoding.     

Distinct and convergent visual processing of high and low spatial frequency information in faces

We tested for differential brain response to distinct spatialfrequency (SF) components in faces. During a functional magneticresonance imaging experiment, participants were presented with"hybrid" faces containing superimposed low and high SF informationfrom different identities. We used a repetition paradigm wherefaces at either SF range were independently repeated or changedacross consecutive trials. In addition, we manipulated whichSF band was attended. Our results suggest that repetition andattention affected partly overlapping occipitotemporal regionsbut did not interact. Changes of high SF faces increased responsesof the right inferior occipital gyrus (IOG) and left inferiortemporal gyrus (ITG), with the latter response being also modulatedadditively by attention. In contrast, the bilateral middle occipitalgyrus (MOG) responded to repetition and attention manipulationsof low SF. A common effect of high and low SF repetition wasobserved in the right fusiform gyrus (FFG). Follow-up connectivityanalyses suggested direct influence of the MOG (low SF), IOG,and ITG (high SF) on the FFG responses. Our results reveal thatdifferent regions within occipitotemporal cortex extract distinctvisual cues at different SF ranges in faces and that the outputsfrom these separate processes project forward to the right FFG,where the different visual cues may converge.     

The interaction of brain regions during visual search processing as revealed by transcranial magnetic stimulation

Although it has long been known that right posterior parietal cortex (PPC) has a role in certain visual search tasks, and human motion area V5 is involved in processing tasks requiring attention to motion, little is known about how these areas may interact during the processing of a task requiring the speciality of each. Using transcranial magnetic stimulation (TMS), this study first established the specialization of each area in the form of a double dissociation; TMS to right PPC disrupted processing of a color/form conjunction and TMS to V5 disrupted processing of a motion/form conjunction. The key finding of this study is, however, if TMS is used to disrupt processing of V5 at its critical time of activation during the motion/form conjunction task, concurrent disruption of right PPC now has a significant effect, where TMS at PPC alone does not. Our findings challenge the conventional interpretation of the role of right PPC in conjunction search and spatial attention.     

Right TPJ deactivation during visual search: functional significance and support for a filter hypothesis

Behavioral performance depends on attending to important objects in the environment rather than irrelevant objects. Regions in the right temporal-parietal junction (TPJ) are thought to be involved in redirecting attention to new objects that are behaviorally relevant. When subjects monitor a stream of distracter objects for a target, TPJ deactivates until the target is detected. We have proposed that the deactivation reflects the filtering of irrelevant inputs from TPJ, preventing unimportant objects from being attended. This hypothesis predicts that the mean deactivation to distracters should be larger when the subsequent target is detected than missed, reflecting more efficient filtering. An analysis of the blood oxygenation level-dependent (BOLD) task-evoked signals from 20 subjects during 2 monitoring tasks confirmed this prediction for regions in right supramarginal gyrus (SMG). Because the deactivation preceded the target, this mean BOLD-detection relationship did not reflect feedback from target detection or postdetection processes. The SMG regions showing this relationship overlapped or neighbored some regions associated with a "default" mode of brain function, suggesting the functional significance of deactivations in some default regions during task performance.     

The rise and fall of priming: how visual exposure shapes cortical representations of objects

How does the amount of time for which we see an object influence the nature and content of its cortical representation? To address this question, we varied the duration of initial exposure to visual objects and then measured functional magnetic resonance imaging (fMRI) signal and behavioral performance during a subsequent repeated presentation of these objects. We report a novel 'rise-and-fall' pattern relating exposure duration and the corresponding magnitude of fMRI cortical signal. Compared with novel objects, repeated objects elicited maximal cortical response reduction when initially presented for 250 ms. Counter-intuitively, initially seeing an object for a longer duration significantly reduced the magnitude of this effect. This 'rise-and-fall' pattern was also evident for the corresponding behavioral priming. To account for these findings, we propose that the earlier interval of an exposure to a visual stimulus results in a fine-tuning of the cortical response, while additional exposure promotes selection of a subset of key features for continued representation. These two independent mechanisms complement each other in shaping object representations with experience.     

Neural system for controlling the contents of object working memory in humans

Working memory (WM), the active maintenance of currently relevant information, is a flexible system allowing for fast and frequent goal-directed changes of rehearsed information. Successful WM maintenance prevents interference from distracting stimuli while allowing new task-relevant information to update the contents of WM. We used functional magnetic resonance imaging to show that when WM contents were updated, regardless of stimulus type (faces or houses), a frontoparietal network showed transient increases in activation. Some of these regions are highly similar to those identified in studies of shifting attention, supporting the idea that updating WM involves a change in the attentional priority afforded to the current perceptual input. A region within the mid-ventrolateral prefrontal cortex, near the junction of the inferior frontal sulcus and precentral sulcus (inferior frontal junction), that has previously been implicated in cognitive control, demonstrated transient increases in activity during updating as well as sustained maintenance activity. A more anterior prefrontal region, middle frontal gyrus, previously implicated in protecting the contents of WM from interfering stimuli during maintenance, demonstrated transient increases in activity during updating. The current study suggests that updating WM results from a combination of increased attention to the visual stimulus and a change in the system's interference protection state.     

A technique for autologous priming of the veno-venous bypass circuit during liver transplantation

Orthotopic liver transplantations (OLT) have been associated with significant blood loss and hemodilution, necessitating significant homologous blood component replacement. Increasing administration of homologous blood products has been found to be inversely related to patient and graft survival. Various methods to reduce the amount of blood products patients receive during OLT, such as antifibrinolytic therapy, thromboelastography-guided transfusion, phlebotomy, reduced central venous pressures intraoperatively, and the use of the veno-venous bypass (VVB) circuit, have been explored.The asanguineous priming volume of the VVB circuit increases the likelihood of the patient receiving homologous blood products due to hemodilution. It was reasoned that autologous priming of the VVB circuit in OLT surgery was a plausible adjunctive blood conservation technique given its application to the extracorporeal circuit during cardiac surgery. We describe our technique of modifying the VVB circuit for autologous priming. This technique adds minimal risk and a small amount of cost to the procedure, requires slightly more communication among members of the surgical team, and with proper sequencing, adds no additional length to the surgical procedure. It is recommended that this technique be considered for addition to the arsenal of blood conservation techniques when VVB is used during OLT.     

Changes in fMRI activation following rehabilitation of reading and visual processing deficits in subjects with traumatic brain injury

In this case series fMRI was used to examine activation patterns during presentation of a reading comprehension (RC) task in three adult subjects with a history of severe traumatic brain injury (TBI). These subjects received cognitive rehabilitation therapy (CRT) for visual processing and acquired reading deficits. fMRI and neuropsychological testing occurred pre- and post-rehabilitation. The study's objective was to evaluate the neurobiological changes using fMRI occurring with CRT and to compare these results to repeat fMRI in matched control subjects. While improvements in neuropsychological testing occurred post-CRT, diffuse and variable activation patterns in the subjects with TBI were still demonstrated when compared to the control subjects repeat imaging. Multiple networks exist to accomplish the complex task of sentence reading and rehabilitation of the cognitive components of reading, such as visual processing; in subjects with TBI, can alter the activation pattern demonstrated during reading comprehension in subjects many years post-injury. This is the first demonstration of changes in network activation patterns post-CRT in patients with severe, chronic TBI on an fMRI task shown to have imaging stability in a normal control sample.     

Evidence for separate perceptual reactivation and search processes during remembering

Remembering involves the coordinated recruitment of strategic search processes and processes involved in reconstructing the content of the past experience. In the present study we used a cueing paradigm based on event-related functional magnetic resonance imaging to separate activity in the initial preparation phases of retrieval from later phases during which retrieval search ensued, and detailed auditory and visual memories were reconstructed. Results suggest a dissociation among inferior temporal (IT) and parieto-occipital (PO) processing regions in how they were influenced by preparatory cues prior to remembering, and indicate a dissociation in how they were influenced by the subsequent validity of those cues during remembering. Regions in IT cortex appeared to show search-related activity during retrieval, as well as robust modality effects, but they were not influenced by preparatory cues. These findings suggest a specific role for IT regions in reconstruction of visual details during remembering. While dorsal regions in parietal and superior occipital cortex also appeared to show search-related activity as well as robust modality effects, they were also influenced by preparatory cues during the retrieval phase, and to a lesser degree during the cue phase. These findings indicate a role in integrating perceptual reactivation and search processes during remembering.     

The prefrontal cortex shows context-specific changes in effective connectivity to motor or visual cortex during the selection of action or colour

The role of the prefrontal cortex remains controversial. Neuroimaging studies support modality-specific and process-specific functions related to working memory and attention. Its role may also be defined by changes in its influence over other brain regions including sensory and motor cortex. We used functional magnetic imaging (fMRI) to study the free selection of actions and colours. Control conditions used externally specified actions and colours. The prefrontal cortex was activated during free selection, regardless of modality, in contrast to modality-specific activations outside prefrontal cortex. Structural equation modelling (SEM) of fMRI data was used to test the hypothesis that although the same regions of prefrontal cortex may be active in tasks within different domains, there is task-dependent effective connectivity between prefrontal cortex and non-prefrontal cortex. The SEM included high-order interactions between modality, selection and regional activity. There was greater coupling between prefrontal cortex and motor cortex during free selection and action tasks, and between prefrontal cortex and visual cortex during free selection of colours. The results suggest that the functions of the prefrontal cortex may be defined not only by selection-specific rather than modality-specific processes, but also by changing patterns of effective connectivity from prefrontal cortex to motor and sensory cortices.     

Priming with anticholinesterases — the effect of different combinations of anticholinesterases and different priming intervals

This study was designed to investigate the effect of different combinations of neostigmine and edrophonium when administered in divided doses and the effect of different intervals (priming intervals) between the doses. Seventy-two patients divided into 12 groups (n = 6 in each) were included in the study. An initial dose of neostigmine 0.012 mg.kg-1 or edrophonium 0.2 mg.kg-1 was administered, followed at different priming intervals (1, 2 or 3 min) by either edrophonium 0.8 mg.kg-1 or neostigmine 0.048 mg.kg-1 for antagonism of atracurium-induced neuromuscular blockade. Reversal was attempted at 10 per cent spontaneous recovery of twitch height. Adequate reversal of neuromuscular block (train-of-four ratio of 0.75) was achieved in all patients. Significant (p less than 0.05) acceleration of the recovery index (time taken for the twitch height to recover from 25 to 75 per cent of control) and reversal time (time taken from the end of injection of the priming dose until TOF ratio value had reached 0.75) was obtained in groups which received edrophonium-edrophonium combination. Recovery indices and reversal times were found to be significantly shorter (p less than 0.05) with a 1 min priming interval. In two additional groups of patients premedicated and anaesthetized as the others equipotent mixtures of the antagonists were administered as a single bolus dose. Reversal times were significantly longer (p less than 0.05) when compared to those given the same amounts of the combination but in divided doses with a 1 min priming interval.(ABSTRACT TRUNCATED AT 250 WORDS)     

fMRI investigation of working memory for faces in autism: visual coding and underconnectivity with frontal areas

Brain activation and functional connectivity were investigated in high functioning autism using functional magnetic resonance imaging in an n-back working memory task involving photographic face stimuli. The autism group showed reliably lower activation compared with controls in the inferior left prefrontal area (involved in verbal processing and working memory maintenance) and the right posterior temporal area (associated with theory of mind processing). The participants with autism also showed activation in a somewhat different location in the fusiform area than the control participants. These results suggest that the neural circuitry of the brain for face processing in autism may be analyzing the features of the face more as objects and less in terms of their human significance. The functional connectivity results revealed that the abnormal fusiform activation was embedded in a larger context of smaller and less synchronized networks, particularly indicating lower functional connectivity with frontal areas. In contrast to the underconnectivity with frontal areas, the autism group showed no underconnectivity among posterior cortical regions. These results extend previous findings of abnormal face perception in autism by demonstrating that the abnormalities are embedded in an abnormal cortical network that manages to perform the working memory task proficiently, using a visually oriented, asocial processing style that minimizes reliance on prefrontal areas.     

Preoperative Functional Magnetic Resonance Imaging (fMRI) of the Motor System in Patients with Tumours in the Parietal Lobe

Summary  Intracranial lesions may compromise structures critical for motor performance, and mapping of the cortex, especially of the motor hand area, is important to reduce postoperative morbidity. We investigated nine patients with parietal lobe tumours and used functional MRI sensitized to changes in blood oxygenation to define the different motor areas, especially the primary sensorimotor cortex, in relation to the localization of the tumour. Activation was determined by pixel-by-pixel correlation of the signal intensity time course with a reference waveform equivalent to the stimulus protocol. All subjects showed significant activation of the primary sensorimotor cortex while performing a finger opposition task with the affected and unaffected side. In five patients the finger opposition task additionally activated the ipsilateral sensorimotor cortex and the supplementary motor area (SMA). Extension and flexion of the foot, additionally performed in two patients, also activated the sensorimotor cortex, in one case within the perifocal oedema of the tumour. Tumour localization near the central sulcus induced displacement of the sensorimotor cortex as compared to the unaffected side in all patients with a relevant mass effect. The results of our study demonstrate that functional MRI at 1.5 T with a clinically used tomograph can reproducibly localize critical brain regions in patients with intracranial lesions.     

A frontoparietal network for spatial attention reorienting in the auditory domain: a human fMRI/MEG study of functional and temporal dynamics

Several studies have identified a supramodal network critical to the reorienting of attention toward stimuli at novel locations and which involves the right temporoparietal junction and the inferior frontal areas. The present functional magnetic resonance imaging (fMRI)\magnetoencephalography (MEG) study investigates: 1) the cerebral circuit underlying attentional reorienting to spatially varying sound locations; 2) the circuit related to the regular change of sound location in the same hemifield, the change of sound location across hemifields, or sounds presented randomly at different locations on the azimuth plane; 3) functional temporal dynamics of the observed cortical areas exploiting the complementary characteristics of the fMRI and MEG paradigms. fMRI results suggest 3 distinct roles: the supratemporal plane appears modulated by variations of sound location; the inferior parietal lobule is modulated by the cross-meridian effect; and the inferior frontal cortex is engaged by the inhibition of a motor response. MEG data help to elucidate the temporal dynamics of this network by providing high-resolution time series with which to measure latency of neural activation manipulated by the reorienting of attention.     

局限减压结合内固定融合治疗退变性腰椎侧凸

目的探讨应用局限神经减压,椎弓根螺钉系统固定加后外侧植骨融合治疗退变性腰椎侧凸的疗效。方法回顾性分析45例退变性腰椎侧凸患者的临床特点,探讨手术适应证和禁忌证,采用局限神经减压、椎弓根螺钉系统内固定和后外侧植骨融合的术式治疗,分析手术效果和并发症,总结术中及术后注意事项,同时对减压和固定融合范围、融合方式等进行探索。结果术后随访24~46个月(平均32个月),临床疗效采用Suk标准评定,植骨融合率88.9%,优良率为93.3%。脑脊液漏1例,神经并发症3例,内固定松动、断裂1例,肺部感染1例,肺栓塞死亡1例。结论采用腰椎管局限神经减压,椎弓根螺钉钉棒系统固定加后外侧植骨融合是治疗退变性腰椎侧凸安全有效的方法,但应严格掌握手术适应证和禁忌证,减压要彻底,但范围不宜过大。     

Onset and effectiveness of rocuronium for rapid onset of paralysis in patients with major burns: priming or large bolus

Background: Burn injury leads to resistance to the effects of non-depolarizingmuscle relaxants. We tested the hypothesis that a larger bolusdose is as effective as priming for rapid onset of paralysisafter burns. Methods: Ninety adults, aged 18–59 yr with 40 (2)% [mean (SE)]burn and 30 (2) days after injury, received rocuronium as apriming dose followed by bolus (0.06+0.94 mg kg^–1), orsingle bolus of either 1.0 or 1.5 mg kg^–1. Sixty-one non-burned,receiving 1.0 mg kg^–1 as a primed (0.06+0.94 mg kg^–1)or full bolus dose, served as controls. Acceleromyography measuredthe onset times. Results: Priming when compared with 1.0 mg kg^–1 bolus in burnedpatients shortened the time to first appearance of twitch depression(30 vs 45 s, P<0.05) and time to maximum twitch inhibition(135 vs 210 s, P<0.05). The onset times between priming andhigher bolus dose (1.5 mg kg^–1) were not different (30vs 30 s for first twitch depression and 135 vs 135 s for maximaldepression, respectively). The onset times in controls, however,were significantly (P<0.05) faster than burns both for primingand for full bolus (15 and 15 s, respectively, for first twitchdepression and 75 and 75 s for maximal depression). Primingcaused respiratory distress in 10% of patients in both groups.Intubating conditions in burns were significantly better with1.5 mg kg^–1 than with priming or full 1.0 mg kg^–1bolus. Conclusions: A dose of 1.5 mg kg^–1 not only produces an initial onsetof paralysis as early as 30 s, which we speculate could be areasonable onset time for relief of laryngospasm, but also hasan onset as fast as priming with superior intubating conditionsand no respiratory side-effects.     

硬膜外利多卡因阻滞时抗室性心律失常的利多卡因给药方案探讨

18例成年病人,随机分成三个组:硬膜外利多卡因3.2mg/kg组,硬膜外利多卡因加1∶20万肾上腺素3.2mg/kg组和静注利多卡因1mg/kg组。利多卡因药时曲线变化规律符合二室开放药代动力学模型,并按一级速率过程进行消除。硬膜外腔注入利多卡因后血药浓度峰值为3.7±1.4μg/ml和2.6+0.6μg/ml,达峰时间为13.5±3.6min和16.4±3.6min。t 1/2Ka为2.901±1.305min和3.464±2.163min.t 1/2β为148.158±41.298min和167.820±34.611 min,CL为6.991±1.124ml/kg/min和6.842±1.820ml/kg/min,Vc为0.677±0.204L/kg和0.946士0.215L/kg。静注利多卡因组Co为3.3士0.8μg/ml,t 1/2β为104.541±50.213min,CL为9.744±2.122ml/kg/min.Vc为0.323士0.127L/kg。本文用药代动力学原理和公式对硬膜外利多卡因阻滞时抗室性心律失常的利多卡因给药方案进行了探讨。