Visuo-spatial imagery impairment in posterior cortical atrophy: a cognitive and SPECT study

This study investigated the cognitive profile and the cerebral perfusion pattern in a highly educated 70 year old gentleman with posterior cortical atrophy (PCA). Visuo-perceptual abilities, spatial memory, spatial representation and navigation, visuo-spatial mental imagery, semantic and episodic-autobiographical memory were assessed. Regional cerebral blood flow (rCBF) was imaged with SPECT. Cognitive testing showed visual-perceptual impairment, apperceptive visual and landmark agnosia, topographical disorientation with way-finding deficits, impaired map learning and poor mental image generation. Semantic memory was normal, while episodic-autobiographical memory was impaired. Reduced rCBF was found mainly in the right hemisphere, in the precentral gyrus, posterior cingulate and middle temporal gyri, cuneus and precuneus, in the left superior temporal and lingual gyri and in the parahippocampus bilaterally. Hypoperfusion in occipito-parietal regions was associated with visuo-spatial deficits, whereas deficits in visuo-spatial mental imagery might reflect dysfunction related to hypoperfusion in the parahippocampus and precuneus, structures which are responsible for spatial and imagery processing. Dissociating performance between preserved semantic memory and poor episodic-autobiographical recall is consistent with a pattern of normal perfusion in frontal and anterior temporal regions but abnormal rCBF in the parahippocampi. The present findings indicate that PCA involves visuo-spatial imagery deficits and provide further validation to current neuro-cognitive models of spatial representation and topographical disorientation.     

Differential prefrontal-temporal neural correlates of semantic processing in children

This study used functional magnetic resonance imaging (fMRI) to examine brain-behavior correlations in a group of 16 children (9- to 12-year-olds). Activation was measured during a semantic judgment task presented in either the visual or auditory modality that required the individual to determine whether a final word was related in meaning to one of two previous words (e.g., found-tank-lost). The main finding was that higher performers (i.e., accuracy) were associated with more activation in posterior representational systems including the inferior and middle temporal gyri, whereas lower performers were associated with more activation in anterior regions including the inferior and middle frontal gyri. This pattern of results was interpreted as reflecting an elaborated semantic representational system in temporal areas for the high accuracy performers that allowed them to efficiently and accurately make meaning based judgments. The low accuracy performers may have an inaccurate or weakly interconnected semantic system that results in greater use of frontal areas in a feature selection process.     

Differential prefrontal–temporal neural correlates of semantic processing in children

This study used functional magnetic resonance imaging (fMRI) to examine brain–behavior correlations in a group of 16 children (9- to 12-year-olds). Activation was measured during a semantic judgment task presented in either the visual or auditory modality that required the individual to determine whether a final word was related in meaning to one of two previous words (e.g., found–tank–lost). The main finding was that higher performers (i.e., accuracy) were associated with more activation in posterior representational systems including the inferior and middle temporal gyri, whereas lower performers were associated with more activation in anterior regions including the inferior and middle frontal gyri. This pattern of results was interpreted as reflecting an elaborated semantic representational system in temporal areas for the high accuracy performers that allowed them to efficiently and accurately make meaning based judgments. The low accuracy performers may have an inaccurate or weakly interconnected semantic system that results in greater use of frontal areas in a feature selection process.     

The functional anatomy of word comprehension and production

This review describes the functional anatomy of word comprehension and production. Data from functional neuroimaging studies of normal subjects are used to determine the distributed set of brain regions that are engaged during particular language tasks and data from studies of patients with neurological damage are used to determine which of these regions are necessary for task performance. This combination of techniques indicates that the left inferior temporal and left posterior inferior parietal cortices are required for accessing semantic knowledge; the left posterior basal temporal lobe and the left frontal operculum are required for translating semantics into phonological output and the left anterior inferior parietal cortex is required for translating orthography to phonology. Further studies are required to establish the specific functions of the different regions and how these functions interact to provide our sophisticated language system.     

Self-referential processing of negative stimuli within the ventral anterior cingulate gyrus and right amygdala

Neural activity associated with self-referential processing of emotional stimuli was investigated using whole brain functional magnetic resonance imaging (fMRI). Fifteen healthy subjects underwent fMRI scanning while making judgments about positive and negative trait words in four conditions (self-reference, other-reference, semantic processing, and letter processing). Significant activity was observed in the right ventral anterior cingulate gyrus and the right amygdala in the negative-word/self-reference condition, and in the left amygdala in the positive-word/self-reference condition. Compared with the semantic-processing condition, the self-reference conditions showed significantly more activity in the medial prefrontal and temporal gyri, posterior cingulate gyrus, and precuneus. These results suggest that the medial prefrontal gyrus, posterior cingulate gyrus, and precuneus are associated with a self-referential processing, and the ventral anterior cingulate gyrus is involved in self-referential processing of negative emotional stimuli. The results also suggest that the amygdala is associated with self-referential processing of both positive and negative emotional stimuli.     

The neural basis of autobiographical and semantic memory: new evidence from three PET studies

A novel, neuropsychologically informed paradigm (extended retrieval of events in response to a cue word) was used to investigate the neural basis of autobiographical and semantic memory. Contrasting retrieval of autobiographical memories with retrieval of semantic facts (ABM-SEM) in 24 subjects across three PET studies revealed bilateral involvement of the middle temporal gyrus (BA 21) and medial frontal cortex (BA 9/10). The opposite contrast, SEM-ABM, resulted in increased regional cerebral blood flow in left posterior temporal regions (BA 37) and left prefrontal cortex (BA 45/46). Laterality maps suggest that the bilateral pattern seen in our studies, but not often in other neuroimaging investigations, reflects the use of a task stressing retrieval of specific personal events. Further comparisons revealed that the activation in the right anterior temporal lobe during autobiographical recall was virtually identical to that seen during retrieval of information about famous people or events in contrast with retrieval of general semantic facts. These findings suggest that the retrieval of an autobiographical event requires participation from conceptual knowledge, and that this type of knowledge is bilaterally distributed in the temporal lobes.     

An event-related fMRI study of syntactic and semantic violations

We used event-related functional magnetic resonance imaging to identify brain regions involved in syntactic and semantic processing. Healthy adult males read well-formed sentences randomly intermixed with sentences which either contained violations of syntactic structure or were semantically implausible. Reading anomalous sentences, as compared to well-formed sentences, yielded distinct patterns of activation for the two violation types. Syntactic violations elicited significantly greater activation than semantic violations primarily in superior frontal cortex. Semantically incongruent sentences elicited greater activation than syntactic violations in the left hippocampal and parahippocampal gyri, the angular gyri bilaterally, the right middle temporal gyrus, and the left inferior frontal sulcus. These results demonstrate that syntactic and semantic processing result in nonidentical patterns of activation, including greater frontal engagement during syntactic processing and larger increases in temporal and temporo-parietal regions during semantic analyses.     

Neural correlates of metacognitive monitoring during episodic and semantic retrieval

Activity in the posterior parietal cortex (PPC) has been shown to be a strong correlate of successful recognition performance. We assessed the degree to which the PPC mediates metacognitive judgments by assessing the feeling of knowing (FOK) for recently learned (episodic) and well-learned (semantic) facts (e.g., "The sport that is associated with Wimbledon is . . ."). Activity in ventral regions of the PPC was observed for strong FOKs for both sets of facts, although greater activity was observed for episodic than for semantic facts. Strong semantic FOKs activated anterior temporal regions. Weaker FOK ratings, when contrasted with strong FOKs, activated dorsal parietal regions, a finding that parallels contrasts during explicit tests in which low-confident responses were compared with high-confident responses. These findings demonstrate retrieval-related parietal activity during metacognitive judgments. Furthermore, they show that the ventral PPC is particularly engaged during context-specific, episodic retrieval, as compared to semantic retrieval.     

Functional connectivity in an fMRI study of semantic and phonological processes and the effect of L-Dopa

We describe an fMRI experiment examining the functional connectivity (FC) between regions of the brain associated with semantic and phonological processing. We wished to explore whether L-Dopa administration affects the interaction between language network components in semantic and phonological categorization tasks, as revealed by FC. We hypothesized that L-Dopa would decrease FC due to restriction of the semantic network. During two test sessions (placebo and L-Dopa) each participant performed two fMRI runs, involving phonological and semantic processing. A number of brain regions commonly activated by the two tasks were chosen as regions if interest: left inferior frontal, left posterior temporal and left fusiform gyri, and left parietal cortex. FC was calculated and further analyzed for effects of either the drug or task. No main effect for drug was found. A significant main effect for task was found, with a greater average correlation for the phonological task than for the semantic task. These findings suggest that language areas are activated in a more synchronous manner for phonological than for semantic tasks. This may relate to the fact that phonological processes are mediated to a greater extent within language areas, whereas semantic tasks likely require greater interaction outside of the language areas. Alternatively, this may be due to differences in the attentional requirements of the two tasks.     

Event-related potential (ERP) evidence for the differential cognitive processing of semantic jokes and pun jokes

Brain-imaging studies report that separate neural correlates are associated with processing of different types of humorous materials. However, such evidence lacks temporal information. In this study, we examined the temporal dynamics of humour comprehension between two types of jokes: semantic (SEMs) and pun (PUNs) jokes, using electroencephalographic (EEG) techniques. Thirty SEMs and 30 PUNs were presented to 16 healthy subjects, and their EEG data were concurrently recorded. PUNs consequently showed a larger N400 amplitude than did SEMs, without a specified scalp site, which implies that PUNs induce greater surprise and semantic violation. Meanwhile, SEMs induced a larger P600-like amplitude at the posterior site, which implies that, in order to understand SEMs, higher working memory loads are needed to form novel associations and successfully frame-shift. A possible explanation is the differing logical mechanisms used to understand SEMs and PUNs: the former builds on semantic relationships, the latter on phonological causality.     

The question shapes the answer: the neural correlates of task differences reveal dynamic semantic processing

Task effects in semantic processing were investigated by contrasting the neural activation associated with two semantic categorization tasks (SCT) using event-related fMRI. The two SCTs involved different decision categories: is it an animal? vs. is it a concrete thing? Participants completed both tasks and, across participants, the same core set of items were presented in both tasks. Results showed task differences in the neural activation associated with these items: in the animal SCT there was greater activation in a number of frontal and temporal regions, including left superior and middle temporal gyri, while in the concrete SCT there was greater activation in left medial frontal gyrus and bilaterally in the precentral gyri. These results are interpreted as evidence of top-down modulation of semantic processing; participants make adjustments to optimize performance in a given task and these adjustments have consequences for the activation observed.     

Aging affects both perceptual and lexical/semantic components of word stem priming: An event-related fMRI study

In this event-related fMRI study, brain activity patterns were compared in extensive groups of young (N=25) and older (N=38) adults, while they were performing a word stem completion priming task. Based on behavioral findings, we tested the hypothesis that aging affects only the lexical/semantic, but not the perceptual component of word stem priming. To this end, we distinguished between priming-related activity reductions in posterior regions involved in visual processing, and regions associated with lexical/semantic retrieval processes, i.e., left lateral temporal and left prefrontal regions. Both groups revealed significant priming-related response time reductions. However, in accordance with earlier findings, a larger priming effect was found in the group of young participants. In line with previous imaging studies, the groups showed common priming-related activity reductions in the anterior cingulate, and the left inferior prefrontal cortex extending into the anterior portion of the left superior temporal gyrus, and at lower thresholds also in the right occipital lobe. However, when directly comparing the groups, greater priming-related reductions were found for the young group in the left anterior superior temporal gyrus and the right posterior occipital lobe. These findings suggest that, converse to current psychological views, aging affects both perceptual and lexical/semantic components of repetition priming.     

Unitary vs multiple semantics: PET studies of word and picture processing

In this paper we examine a central issue in cognitive neuroscience: are there separate conceptual representations associated with different input modalities (e.g., Paivio, 1971, 1986; Warrington & Shallice, 1984) or do inputs from different modalities converge on to the same set of representations (e.g., Caramazza, Hillis, Rapp, & Romani, 1990; Lambon Ralph, Graham, Patterson, & Hodges, 1999; Rapp, Hillis, & Caramazza, 1993)? We present an analysis of four PET studies (three semantic categorisation tasks and one lexical decision task), two of which employ words as stimuli and two of which employ pictures. Using conjunction analyses, we found robust semantic activation, common to both input modalities in anterior and medial aspects of the left fusiform gyrus, left parahippocampal and perirhinal cortices, and left inferior frontal gyrus (BA 47). There were modality-specific activations in both temporal poles (words) and occipitotemporal cortices (pictures). We propose that the temporal poles are involved in processing both words and pictures, but their engagement might be primarily determined by the level of specificity at which an object is processed. Activation in posterior temporal regions associated with picture processing most likely reflects intermediate, pre-semantic stages of visual processing. Our data are most consistent with a hierarchically structured, unitary system of semantic representations for both verbal and visual modalities, subserved by anterior regions of the inferior temporal cortex.     

Neuroanatomical correlates of oral reading in acute left hemispheric stroke

Oral reading is a complex skill involving the interaction of orthographic, phonological, and semantic processes. Functional imaging studies with nonimpaired adult readers have identified a widely distributed network of frontal, inferior parietal, posterior temporal, and occipital brain regions involved in the task. However, while functional imaging can identify cortical regions engaged in the process under examination, it cannot identify those brain regions essential for the task. The current study aimed to identify those neuroanatomical regions critical for successful oral reading by examining the relationship between word and nonword oral reading deficits and areas of tissue dysfunction in acute stroke. We evaluated 91 patients with left hemisphere ischemic stroke with a test of oral word and nonword reading, and magnetic resonance diffusion-weighted and perfusion-weighted imaging, within 24-48 h of stroke onset. A voxel-wise statistical map showed that impairments in word and nonword reading were associated with a distributed network of brain regions, including the inferior and middle frontal gyri, the middle temporal gyrus, the supramarginal and angular gyri, and the middle occipital gyrus. In addition, lesions associated with word deficits were found to be distributed more frontally, while nonword deficits were associated with lesions distributed more posteriorly.     

Shindigs,brunches, and rodeos: The neural basis of event words

Events (e.g., “running” or “eating”) constitute a basic type within human cognition and human language. We asked whether thinking about events, as compared to other conceptual categories, depends on partially independent neural circuits. Indirect evidence for this hypothesis comes from previous studies showing elevated posterior temporal responses to verbs, which typically label events. Neural responses to verbs could, however, be driven either by their grammatical or by their semantic properties. In the present experiment, we separated the effects of grammatical class (verb vs. noun) and semantic category (event vs. object) by measuring neural responses to event nouns (e.g., “the hurricane”). Participants rated the semantic relatedness of event nouns, as well as of two categories of object nouns—animals (e.g., “the alligator”) and plants (e.g., “the acorn”)—and three categories of verbs—manner of motion (e.g., “to roll”), emission (e.g., “to sparkle”), and perception (e.g., “to gaze”). As has previously been observed, we found larger responses to verbs than to object nouns in the left posterior middle (LMTG) and superior (LSTG) temporal gyri. Crucially, we also found that the LMTG responds more to event than to object nouns. These data suggest that part of the posterior lateral temporal response to verbs is driven by their semantic properties. By contrast, a more superior region, at the junction of the temporal and parietal cortices, responded more to verbs than to all nouns, irrespective of their semantic category. We concluded that the neural mechanisms engaged when thinking about event and object categories are partially dissociable.     

新颖语义联结形成的右半球优势效应

新颖语义联结形成是创造性思维的重要加工过程。采用谜题型歇后语为材料,直接操控语义联结的新颖性,通过两个实验考察汉语新颖语义联结形成的神经机制。实验1采用fMRI记录谜题型歇后语阅读理解过程的神经活动,结果显示相对于寻常语义关联条件,新颖语义关联条件更强地激活了右侧颞上回,该脑区可能与新颖语义信息的激活有关。实验2采用ERP技术在语义关联性判断任务中考察新颖语义联结形成神经加工的时空特征,结果显示相对于寻常语义关联条件,新颖语义关联条件在右侧颞区和右侧额区诱发了更正的晚期正成分,可能分别反映了新颖语义信息的激活以及选择与整合。研究结果支持了新颖语义联结形成的右半球加工优势效应。     

顿悟的大脑机制

自从柯勒1917年提出顿悟的概念以来,这个问题一直吸引着心理学家的关注。但有关顿悟过程的精确的大脑机制却始终未被触及。从心理过程上看,顿悟是一个瞬间实现的、问题解决视角的“新旧交替”过程;它包含两个方面,一是新的有效的问题解决思路如何实现,二是旧的无效的思路如何被抛弃（即打破思维定势）。我们以谜语作为材料,利用功能性磁共振成像（fMRI）技术精确记录了人类的大脑在实现顿悟的一瞬间的活动状况。结果显示顿悟过程激活了包括额叶、颞叶、扣带前回、以及海马在内的广泛脑区。根据各方面的综合证据,本文认为：顿悟过程中,新异而有效的联系的形成依赖于海马,问题表征方式的有效转换依赖于一个“非语言的” 视觉空间信息加工网络,而思维定势的打破与转移则依赖于扣带前回与左腹侧额叶。     

新颖语义联结在顿悟促进记忆效果中的作用

采用成语谜题选择任务, 通过学习-测验范式探究顿悟促进记忆的认知神经机制。实验1采用行为实验, 验证成语谜题选择范式在探究顿悟促进记忆中的有效性, 结果显示, 相比于寻常联结条件, 新颖联结条件下被试在学习阶段具有更高的顿悟感得分, 在测试阶段具有更高的正确率, 范式的有效性得以验证。实验2采用fMRI技术探究顿悟促进记忆的关键脑区。结果显示, 相比于失败记忆新颖联结条件, 成功记忆新颖联结条件更强地激活了顿悟过程相关脑区, 包括海马、杏仁核、额中回、颞上回和颞中回。这说明在学习阶段的顿悟问题解决过程中, 对信息的深加工与积极情绪促进了随后的记忆; 对其进一步分析发现, 相比于寻常联结记忆, 新颖联结对记忆的促进效应主要与右侧海马激活有关, 它可能反映了在顿悟问题解决中新颖联结形成过程建立了情节记忆以及新颖且有价值的语义联结。研究结果表明新颖语义联结形成在顿悟促进记忆中发挥了重要作用。     

创造性思维四阶段的神经基础

华莱士(Wallas)四阶段论是创造性思维过程研究的重要模型, 该模型认为创造性思维包括准备期、酝酿期、明朗期、验证期。相关神经机制研究表明, 准备期主要包括题目呈现前大脑状态和静息状态的研究, 内侧额叶/ACC及颞叶构成准备期网络; 酝酿期主要包括酝酿期提示、延迟顿悟以及心智游移的相关研究, 这一阶段涉及左右脑的共同参与, 海马、腹内侧前额叶等脑区在酝酿过程中起重要作用; 现有顿悟研究反映明朗期和验证期神经活动, 前额叶、扣带回、颞上回、海马、楔叶、楔前叶、舌回、小脑等在内的脑区构成其神经基础, 其中, 扣带回、前额叶在不同角度进行的研究中均有参与, 颞上回是负责远距离联想的关键脑区, 海马参与定势打破与新颖联系形成, 外侧额叶是定势转移的关键脑区, 楔前叶、左侧额下/额中回、舌回在原型激活中起关键作用, 左外侧前额叶参与对答案细节性的验证加工。未来研究可从研究对象、研究内容、研究手段三方面加以改进, 以对创造性思维过程作更系统的探讨。     

Preserved ability to recognize keywords related to remote events in the absence of retrieval of relevant knowledge: a case of postencephalitic amnesia

We describe a case of severe anterograde and retrograde amnesia resulting from herpes simplex encephalitis. Magnetic resonance imaging revealed pathological changes in the bilateral hippocampi, parahippocampal gyri, fusiform gyri, medial temporal poles, posterior part of the cingulate gyri, and insula. The patient showed severe amnesia for autobiographical episodic memory in relation to events that had occurred throughout her life, but temporally graded amnesia for autobiographical semantic memory, and severe amnesia without a temporal gradient for public events and famous people. However, using a multiple-choice method, she showed a high level of accuracy when choosing keywords related to public or personal events, although this did not prompt her recollection of the events. An important indication of these results is that, even with severe retrograde amnesia, memories of past events are not completely lost. We propose that an event may be stored in a fragmented form, consisting of many components, and that normal recall of an event may require recombination or reconstruction of these components.