Prefrontal, parietal, and temporal cortex networks underlie decision-making in the presence of uncertainty

Decision-making in the presence of uncertainty, i.e., selecting a sequence of responses in an uncertain environment according to a self-generated plan of action, is a complex activity that involves both cognitive and noncognitive processes. Using functional magnetic resonance imaging, the neural substrates of decision-making in the presence of uncertainty are examined. Normal control subjects show a significant activation of a frontoparietal and limbic neural system during a two-choice prediction task relative to a two-choice response task. The most prevalent response strategy during the two-choice prediction task was "win-stay/lose-shift," where subjects will repeat the previous response if it successfully predicted the stimulus and switch to the alternative response otherwise. Increased frequency of responses that are consistent with this strategy is associated with activation in the superior temporal gyrus. In comparison, increased frequency of response inconsistent with win-stay/lose-shift is associated with parietal cortex activation. These results support the hypothesis that subjects use a frontoparietal neural system to establish a contingency based decision-making strategy even in the presence of random reinforcement.     

1例额颞顶叶脑梗死引起单侧肢体忽略自伤病人的护理

脑梗死是指局部脑组织包括神经细胞、胶质细胞和血管由于血液供应缺乏而发生的坏死[1]。额叶、颞叶、顶叶损害的病人常伴有一些精神症状:额叶病变表现精神活动方面的障碍,易出现痴呆、人格改变及病变对侧上肢强握与摸索反射;颞叶病变表现为幻嗅幻味、错觉幻觉、自动症及似曾相识症、旧事如新或生疏感、精神异常、内脏症状、情感异常及抽搐;顶叶病变时出现计算不能、不能识别手指、左右侧认识不能和书写不能;右侧顶叶邻近角回损害易出现自体认识不能:表现为不认识自己患侧身体的存在,认为左侧上下肢不是自己的;右侧顶叶邻近缘上回处损害出现…     

1例额颞顶叶脑梗死引起单侧肢体忽略自伤病人的护理

脑梗死是指局部脑组织包括神经细胞、胶质细胞和血管由于血液供应缺乏而发生的坏死。额叶、颞叶、顶叶损害的病人常伴有一些精神症状：额叶病变表现精神活动方面的障碍，易出现痴呆、人格改变及病变对侧上肢强握与摸索反射；颞叶病变表现为幻嗅幻味、错觉幻觉、自动症及似曾相识症、旧事如新或生疏感、精神异常、内脏症状、情感异常及抽搐；     

脑灌注磁共振成像观察内侧颞叶癫痫部分及继发全面发作

目的观察部分及继发全面发作内侧颞叶癫痫(mTLE)患者脑区灌注的差异,分析在继发全面发作中起作用的相关脑区,探讨继发全面发作的mTLE网络的相关脑区。方法选取51例mTLE患者,其中16例部分发作(PS组),35例部分发作继发全面发作(sGS组)。利用3.0T MR脉冲式动脉自旋标记(PASL)序列采集两组患者发作间期脑血流量(CBF)数据。采用体素依赖统计分析(VBA)技术对两组患者脑灌注存在差异的脑区进行评价;并基于此选取患侧颞叶、丘脑及额叶等区域作为ROI,分别评价两组患者各ROI间的CBF的相关性。结果与PS组相比(校正后,P<0.05),sGS组患者表现为发作间期患侧丘脑、基底核及部分默认模式网络区域如双侧楔前叶、前扣带回、后扣带回、内侧前额叶等CBF降低;sGS组患者患侧颞叶与额叶(r=0.50,P<0.05)、丘脑与额叶(r=0.36,P<0.05)的CBF均有明显相关性。结论丘脑在继发全面发作的癫痫活动传播中起重要作用;癫痫活动通过特定网络传播到远处脑区。部分发作继发全面发作mTLE患者相比部分性发作患者部分脑区功能受损更严重。     

全面强直阵挛癫痫静息态功能连接脑网络研究

目的 采用静息态功能MRI (fMRI)功能连接分析技术,观察全面强直阵挛癫痫患者发作间期静息态脑网络的改变,探讨强直阵挛癫痫的病理生理机制.方法 52例全面强直阵挛癫痫患者与57名止常志愿者(对照组)参与了,本研究.采集闭眼静息态fMRI数据.分别以双侧丘脑,双侧后扣带皮质为种子点,观察丘脑网络、默认网络(DMN)在患者中的功能改变.结果 组内单样本t检验结果提示,以双侧丘脑为种子点的功能连接模式主要分布于额顶叶,而以双侧后扣带皮质为种子点的功能连接模式主要表现为默认网络.进一步组间比较发现,患者的丘脑与双侧运动皮层及右侧岛叶的功能连接增强,而与DMN脑区及基底节的功能连接减弱;而DMN内部与后扣带皮质的功能连接在双侧颞极、内侧前额叶和缘上回的功能连接减弱,而与双侧角回、丘脑和左侧额上回的功能连接增强.结论 丘脑是强直阵挛癫痫网络的重要节点,它与运动皮层间增强的功能连接可能与癫痫发作时患者肌肉的强直阵挛有关.而默认网络内功能连接的异常可能与癫痫发作时的意识丧失有关.即使在发作间期,全面强直阵挛癫痫的脑功能也有着显著改变.     

The effect of medial frontal and posterior parietal demyelinating lesions on stroop interference

Functional imaging has consistently shown that attention-related areas of medial frontal and posterior parietal cortices are active during the attentional conflict induced by color naming in the presence of distracting words (Stroop task). Such studies, however, have provided few details of the correlational nature between observed regional brain activations and reaction time delay occurring in this situation. We analyzed the effect of medial frontal and posterior parietal lesions on the Stroop response in a group of patients with multiple sclerosis, a neurological disorder in which Stroop response speed is affected to varying degrees. Forty-five patients were assessed using a computer-presented verbal version of the Stroop task and specific MRI protocol. Demyelination areas were measured on five anatomical divisions of the medial frontal white matter and on white matter of the posterior parietal lobe. We found that a combination of frontal and parietal lesion measurements accounted for 45% of the Stroop interference time variance. Patients with more right frontal than left parietal demyelination showed slowed Stroop responses, whereas the predominance of lesions in the left posterior parietal region was associated with a reduced Stroop interference. These results may contribute to defining the specific participation of these attention-related brain areas in the conflict of attention represented by the Stroop paradigm. They also help to explain the variability of the Stroop effect in multiple sclerosis patients and suggest that the Stroop test does not assess just a single cognitive operation, but rather the combined effect of anatomically segregated neural processes.     

额叶、颞叶肿瘤事件相关电位P3的研究

目的　研究额叶、颞叶肿瘤患者事件相关电位P3各项参数的变化特点,探讨P3的发生源。方法　采用视觉分辨刺激序列测查P3,选取额叶、颞叶肿瘤占位患者各15例。结果　颞叶肿瘤占位患者P3潜伏期、地形图等参数变化明显,而额叶则无明显变化。结论　由此推断颞叶皮层对P3的发生有重要贡献。通过分析P3潜伏期、波幅、面积及地形图各项参数,认为P3潜伏期、地形图可以较好地反映脑内处理器激活的时间和程度,以及P3与各脑叶的关系,是研究P3的可靠的、客观的参数。     

Viewing the motion of human body parts activates different regions of premotor, temporal, and parietal cortex

Activation of premotor and temporoparietal cortex occurs when we observe others movements, particularly relating to objects. Viewing the motion of different body parts without the context of an object has not been systematically evaluated. During a 3T fMRI study, 12 healthy subjects viewed human face, hand, and leg motion, which was not directed at or did not involve an object. Activation was identified relative to static images of the same human face, hand, and leg in both individual subject and group average data. Four clear activation foci emerged: (1) right MT/V5 activated to all forms of viewed motion; (2) right STS activated to face and leg motion; (3) ventral premotor cortex activated to face, hand, and leg motion in the right hemisphere and to leg motion in the left hemisphere; and (4) anterior intraparietal cortex (aIP) was active bilaterally to viewing hand motion and in the right hemisphere leg motion. In addition, in the group data, a somatotopic activation pattern for viewing face, hand, and leg motion occurred in right ventral premotor cortex. Activation patterns in STS and aIP were more complex--typically activation foci to viewing two types of human motion showed some overlap. Activation in individual subjects was similar; however, activation to hand motion also occurred in the STS with a variable location across subjects--explaining the lack of a clear activation focus in the group data. The data indicate that there are selective responses to viewing motion of different body parts in the human brain that are independent of object or tool use.     

Bupropion seizure proportion among new-onset generalized seizures and drug related seizures presenting to an emergency department

Bupropion is a relatively new and popular medication with seizures as its major side effect. This drug can produce seizures with an overdose. The purpose of this investigation was to determine the relative importance of this medication as the etiology of new-onset seizures relative to other drugs and new-onset seizures in general. The study design was a retrospective case series. All new onset generalized seizures were evaluated over a 4-year period in subjects 16 years of age and older. Etiologic diagnosis was determined from the neurology consultation and all patients with new-onset seizures were admitted to the hospital as per hospital policy and received a routine chemistry screening and a neuroimaging study as a minimum. The results indicate that 17 of 279 or 6.1% of the new-onset seizures were drug related. After cocaine intoxication (6/279 or 2.2%) and benzodiazepine withdrawal (5/279 or 1.8%) seizures, bupropion (4/279 or 1.4%) was the third leading cause of drug related seizures. In addition, all the bupropion related seizures occurred in patients taking what was considered to be a therapeutic dose or 450 mg/day or less. Sleep deprivation, previous history of attention deficit disorder and bulimia, and previous heavy alcohol use were associated in three of the patients taking bupropion who had seizures. We conclude that although drug related new-onset seizures are not a common cause of seizures overall, bupropion might be a more common cause of drug related new-onset generalized seizures presenting to the Emergency Department than previously thought, occurring in more than one-fifth of this subgroup of cases. Possibly, greater exclusion criteria are needed than currently recommended for the use of bupropion at therapeutic doses.     

Increased water diffusivity in the frontal and temporal cortices of schizophrenic patients

Schizophrenia has been suggested to be the result of both macroscopic and microscopic abnormalities in the brain. Although no definitive clinico-pathological correlations have been found to reconcile the many facets inherent in this disorder, the recent development of the magnetic resonance diffusion tensor imaging (DTI) has allowed us to gather useful information regarding the microcircuitry of the brain. Specifically, the apparent diffusion coefficient (ADC) reflects the degree of diffusion barriers and heterosynaptic communication for the brain neurotransmitter. Nineteen patients with DSM-IV schizophrenia and 21 age- and sex-matched control subjects participated in DTI, and the severity of the patients' symptoms was evaluated according to the Positive and Negative Syndrome Scale (PANSS). The ADC values were determined and compared between patients and control subjects via voxel-based morphometry. The results show an increased ADC in the bilateral fronto-temporal regions of the schizophrenic patients, as compared with those of the control subjects. In addition, the ADC values in the area of the right insular were correlated with the negative syndromes from the PANSS. Our findings of increased water diffusivity in the fronto-temporal regions of schizophrenic patients and the correlation between negative symptom scales and the ADC in the right insular region indicate that damaged brain microcircuitry might contribute to the pathophysiology of schizophrenia. These findings contribute towards integrating micro and macrostructural abnormalities and syndromes of schizophrenia.     

Event-related optical imaging reveals the temporal dynamics of right temporal and frontal cortex activation in pre-attentive change detection

The mismatch negativity (MMN) is a pre-attentive brain response to auditory environmental change. Temporal and frontal cortex generators of pre-attentive change detection have been proposed based on source localization of event-related potentials (ERP), positron emission tomography (PET), and functional magnetic resonance imaging (fMRI) studies. The temporal cortex generators are believed to underlie change detection, whereas the frontal cortex generators are thought to subserve reorientation of attention in response to change. The present study used the event-related optical signal (EROS), an imaging technique that is sensitive to activity related changes in the light scattering properties of neurons, to investigate the pre-attentive brain response to stimulus omissions. The stimulus train comprised 10 ms tone pips presented with a stimulus onset asynchrony (SOA) of 84 ms. Occasional tone omissions elicited a significant increase in right superior temporal gyrus (STG) activity 140 ms after the omitted stimulus, followed 60 ms later by right inferior frontal gyrus (IFG) activity. This result provides support for a temporal-frontal cortical network that underlies pre-attentive change detection.     

Comparison of impaired subcortico-frontal metabolic networks in normal aging, subcortico-frontal dementia, and cortical frontal dementia.

Normal aging, progressive supranuclear palsy (PSP), and frontotemporal dementia (FTD) are characterized by different degrees of decline in frontal lobe functions. We used (18)FDG-PET and statistical parametric mapping (SPM96) to compare relative subcorticofrontal metabolic impairment at rest in 21 healthy elderly subjects (HES), 20 PSP patients, and 6 FTD patients. When HES were compared to 22 healthy young subjects, widespread decrease in metabolism was observed in bilateral medial prefrontal areas including anterior cingulate cortices, in dorsolateral prefrontal areas, in left lateral premotor area, in Broca's area, and in left insula. In PSP compared to the 43 healthy subjects (HS), we observed subcorticofrontal metabolic impairment including both motor and cognitive neural networks. Impairment of functional connections between midbrain tegmentum and cerebellar, temporal and pallidal regions was demonstrated in PSP as compared to HS. When comparing FTD to HS, glucose uptake was primarily reduced in dorsolateral and ventrolateral prefrontal cortices and in frontopolar and anterior cingulate regions. There was also bilateral anterior temporal, right inferior parietal, and bilateral striatal hypometabolism. Finally, FTD showed more severe striatofrontal metabolic impairment than PSP, while mesencephalothalamic involvement was only observed in PSP. Our data suggest that subcorticofrontal metabolic impairment is distributed in distinct subcorticocortical networks in normal aging, PSP, and FTD. Subcorticofrontal dementia in PSP is related to hypometabolism in discrete frontal areas, which are probably disconnected from certain subcortical structures. The concept of subcortical dementia is reinforced by our data, which show disrupted functional connections between mesencephalon and cerebellar cortex, inferior and medial temporal regions, and pallidum.     

Separate time behaviors of the temporal and frontal mismatch negativity sources

It has been proposed that mismatch negativity (MMN) is generated by temporal and frontal lobe sources, the former being associated with change detection and the latter with involuntary switching of attention to sound change. If this switching of attention is triggered by the temporal cortex change-detection mechanism, one would expect that the frontal component of MMN is activated later than the temporal one. This was studied by using 64-channel electroencephalography (EEG) and 122-channel magnetoencephalography (MEG) with realistically shaped head models to determine the source current distribution in different lobes as a function of time. Minimum-norm estimation (MNE) was performed, constraining the solution to the reconstructed cortical sheet. The results support the hypothesis that the frontal MMN generator is activated later than the auditory cortex generator.     

Cue validity modulates the neural correlates of covert endogenous orienting of attention in parietal and frontal cortex

Parietal brain regions have been implicated in reorienting of visuospatial attention in location-cueing paradigms when misleading advance information is provided in form of a spatially invalid cue. The difference in reaction times to invalidly and validly cued targets is termed the "validity effect" and used as a behavioral measure for attentional reorienting. Behavioral studies suggest that the magnitude of the validity effect depends on the ratio of validly to invalidly cued targets (termed cue validity), i.e., on the amount of top-down information provided. Using fMRI, we investigated the effects of a cue validity manipulation upon the neural mechanisms underlying attentional reorienting using valid and invalid spatial cues in the context of 90% and 60% cue validity, respectively. We hypothesized that increased parietal activation would be elicited when subjects need to reorient their attention in a context of high cue validity. Behaviorally, subjects showed significantly higher validity effects in the high as compared to the low cue validity condition, indicating slower reorienting. The neuroimaging data revealed higher activation of right inferior parietal and right frontal cortex in the 90% than in the 60% cue validity condition. We conclude that the amount of top-down information provided by predictive cues influences the neural correlates of reorienting of visuospatial attention by modulating activation of a right fronto-parietal attentional network.     

Abnormalities of language networks in temporal lobe epilepsy

Functional magnetic resonance imaging (fMRI) in patients with temporal lobe epilepsy (TLE) has demonstrated reorganisation of language functions with greater involvement of the non-dominant hemisphere. The structural brain connections supporting this atypical language dominance have not previously been identified. We performed fMRI of language functions and imaging of white matter connections using MR tractography in 14 patients with unilateral TLE and hippocampal sclerosis and 10 controls. Verb generation and reading comprehension paradigms were used to define functional regions which were used to generate starting regions for tractography. Controls and right TLE patients had a left-lateralised pattern of both language-related activations and the associated structural connections. Left TLE patients showed more symmetrical language activations, along with reduced left hemisphere and increased right hemisphere structural connections. Subjects with more lateralised functional activation had also more highly lateralised connecting pathways. We provide evidence for structural reorganisation of white matter tracts that reflects the altered functional language lateralisation in left TLE patients. The combination of fMRI and tractography offers a promising tool for studying the reorganisation of language functions in many neurological conditions and may prove useful in predicting language deficits following temporal lobe surgery.     

Differential correlation of frontal and parietal activity with the number of alternatives for cued choice saccades

Temporal processing underlies many aspects of human perception, performance and cognition. The present study used fMRI to examine the functional neuroanatomy of a temporal discrimination task and to address two questions highlighted by previous studies: (1) the effect of task difficulty on neuronal activation and (2) the involvement of the dorsolateral prefrontal cortex (DLPFC) in timing. Twenty healthy subjects were scanned while either judging whether the second in a pair of tones was shorter or longer in duration than the standard tone or simply responding to the presentation of two identical tones as a control condition. Two levels of difficulty were studied. Activation during the less difficult condition was observed only in the cerebellum and superior temporal gyrus. As difficulty increased, additional activation of the supplementary motor area, insula/operculum, DLPFC, thalamus and striatum was observed. These results suggest the cerebellum plays a critical role in timing, particularly in gross temporal discrimination. These results also suggest that recruitment of frontal and striatal regions during timing tasks is load-dependent. Additionally, robust activation of the dorsolateral prefrontal cortex under conditions of minimal working memory involvement supports the specific involvement of this region in temporal processing rather than a more general involvement in working memory.     

Dissociable networks involved in spatial and temporal order source retrieval

Space and time are important components of our episodic memories. Without this information, we cannot determine the "where and when" of our recent memories, rendering it difficult to disambiguate individual episodes from each other. The neural underpinnings of spatial and temporal order memory in humans remain unclear, in part because of difficulties in disentangling the contributions of these two types of source information. To address this issue, we conducted an experiment in which participants first navigated a virtual city, experiencing unique routes in a specific temporal order and learning about the spatial layout of the city. Spatial and temporal order information were dissociated in our task such that learning one type of information did not facilitate the other behaviorally. This allowed us to then address the extent to which the two types of information involved functionally distinct or overlapping brain areas. During functional magnetic resonance imaging (fMRI), participants retrieved information about the relative distance of stores within the city (spatial task) and the temporal order of stores from each other (temporal task). Comparable hippocampal activity was observed during these two tasks, but greater prefrontal activity was seen during temporal order retrieval whereas greater parahippocampal activity was seen during spatial retrieval. We suggest that while the brain possesses dissociable networks for maintaining and representing spatial layout and temporal order components of episodic memory, this information may converge into a common representation for source memory in areas such as the hippocampus.     

Differential activation of frontal and parietal regions during visual word recognition: an optical topography study

The present study examined cortical oxygenation changes during lexical decision on words and pseudowords using functional Near-Infrared Spectroscopy (fNIRS). Focal hyperoxygenation as an indicator of functional activation was compared over three target areas over the left hemisphere. A 52-channel Hitachi ETG-4000 was used covering the superior frontal gyrus (SFG), the left inferior parietal gyrus (IPG) and the left inferior frontal gyrus (IFG). To allow for anatomical inference a recently developed probabilistic mapping method was used to determine the most likely anatomic locations of the changes in cortical activation [Tsuzuki, D., Jurcak, V., Singh, A.K., Okamoto, M., Watanabe, E., Dan, I., 2007. Virtual spatial registration of stand-alone fNIRS data to MNI space. NeuroImage 43 (4), 1506-1518. Subjects made lexical decisions on 50 low and 50 high frequency words and 100 pseudowords. With respect to the lexicality effect, words elicited a larger focal hyperoxygenation in comparison to pseudowords in two regions identified as the SFG and left IPG. The SFG activation difference was interpreted to reflect decision-related mechanisms according to the Multiple Read-Out Model [Grainger, J., Jacobs, A.M., 1996. Orthographic processing in visual word recognition: A multiple read-out model. Psychological Review 103, 518-565]. The greater oxygenation response to words in the left IPG suggests that this region connects orthographic, phonological and semantic representations. A decrease of deoxygenated hemoglobin was observed to low frequency in comparison to high frequency words in a region identified as IFG. This region's sensitivity to word frequency suggests its involvement in grapheme-phoneme conversion, or its role during the selection of pre-activated semantic candidates.     

Intravenous versus intramuscular midazolam in treatment of chemically induced generalized seizures in swine

Midazolam is a water-soluble benzodiazepine proven to be efficacious in sedation, hypnosis, and induction and maintenance of anesthesia. Because of its water solubility, it is a desirable drug for the control of status epilepticus when intravenous (IV) access is not obtainable. This study compares intramuscular (IM) versus IV routes of administration of midazolam in the control of tonic-clonic activity produced by chemically induced generalized seizures in a swine model. When midazolam was administered by IV route, tonic-clonic activity lasted a mean of 34 ± 5.4 seconds, and when administered by IM route, the tonic-clonic activity lasted a mean of 116 ± 41 seconds. Both were considerably abbreviated when compared with the expected duration of pentylenetetrazol-induced seizures in the swine model. Serum levels of midazolam achieved by the IV route were considerably higher than those achieved by the IM route. It is concluded that midazolam is effective in the control of tonic-clonic manifestations of generalized seizures when administered by the IV or the IM route and that no correlation exists between serum levels achieved and the time to control the seizure.