An fMRI study of sex differences in regional activation to a verbal and a spatial task

Sex differences in cognitive performance have been documented, women performing better on some phonological tasks and men on spatial tasks. An earlier fMRI study suggested sex differences in distributed brain activation during phonological processing, with bilateral activation seen in women while men showed primarily left-lateralized activation. This blood oxygen level-dependent fMRI study examined sex differences (14 men, 13 women) in activation for a spatial task (judgment of line orientation) compared to a verbal-reasoning task (analogies) that does not typically show sex differences. Task difficulty was manipulated. Hypothesized ROI-based analysis documented the expected left-lateralized changes for the verbal task in the inferior parietal and planum temporal regions in both men and women, but only men showed right-lateralized increase for the spatial task in these regions. Image-based analysis revealed a distributed network of cortical regions activated by the tasks, which consisted of the lateral frontal, medial frontal, mid-temporal, occipitoparietal, and occipital regions. The activation was more left lateralized for the verbal and more right for the spatial tasks, but men also showed some left activation for the spatial task, which was not seen in women. Increased task difficulty produced more distributed activation for the verbal and more circumscribed activation for the spatial task. The results suggest that failure to activate the appropriate hemisphere in regions directly involved in task performance may explain certain sex differences in performance. They also extend, for a spatial task, the principle that bilateral activation in a distributed cognitive system underlies sex differences in performance.     

Effect of short lateralized signals on arousal versus activation on tasks requiring visuospatial or elementary semantic stimulus processing

The results of the experiment offer indirect evidence for the basic hypothesis that the brain self-regulates its own arousal and activation as a function of the intensity and type of ongoing cortical activity. When subjects perform a task which can be assumed to be primarily attended to by the right hemisphere, the result of a supplementary information-processing load seems to be increased arousal. On a task primarily attended to by the left hemisphere, the consequence is increased activation. The evidence is indirect because no measurements have been made of the neurological events and processes which are assumed to intervene in this self-regulation process. Although indirect, the evidence may help to formulate more precise psychological hypotheses about the factors controlling the putative effort system which, according to Pribram and McGuinness in 1975, coordinates the arousal and activation of cerebral processes.     

The phonological-similarity effect differentiates between two working memory tasks

Working memory is a set of interactive cognitive processes that maintain information on–line and available for analysis. Part of the system is specialized for maintaining verbal information, a core component of which is thought to be a phonological store. On the basis of the study of patients with acquired brain lesions, this store has been localized to the supramarginal and angular gyri of the speech–dominant hemisphere, and some functional neuroimaging studies support this localization. However, other imaging studies localize the phonological store in a more dorsal region of the parietal lobe. To reconcile these findings, we examined the phonological–similarity effect in two different tasks. A phonological–similarity effect was observed only in the task that involved sequential presentation and explicit verbal rehearsal. We conclude that at least one possible source of the differences in brain activation between different working memory tasks may be differences in phonological processing.     

Behavioral performances in participants with phonological dyslexia and different patterns on the N170 component

Adults with phonological dyslexia and controls performed a lexical decision task while ERPs were recorded in the occipitotemporal pathway. Based on N170 durations, two subgroups were formed: dysl1 showing longer N170 durations and dysl2 showing normal N170 durations. While the dysl1 subgroup had poorer accuracy for infrequent words and pseudo-words, the dysl2 group responded more slowly than controls to pseudo-words. N170 amplitudes were larger in the left hemisphere for controls irrespective of items. In the dysl1 subgroup, N170 amplitudes were larger in the left hemisphere than the right for words but not for pseudo-words, a sign of hemispheric compensation, while in the dysl2 subgroup signs of bilateralization were observed. Moreover, in the dysl1 subgroup, P100 amplitudes were smaller than controls. These results indicate different behavioral profiles of dyslexics with different patterns of P100 and N170 components. The ERP changes may be due to different behavioral strategies employed by each subgroup, logographic in dysl2 and phonological in dysl1.     

类别性空间记忆右侧化优势及其受威胁情境的影响

以往研究发现类别空间关系表征具有左半球激活优势,但在行为表现中是否存在对侧化的右侧化优势尚且不明确。本研究采用两个被试内实验,探讨空间记忆的行为表现是否具有右侧化优势以及这种优势是否受威胁情境的影响。实验1被试学习完一幅模拟地图中物体位置关系后进行相对位置判断任务,结果发现了显著的空间行为反应右侧化优势。实验2使被试在威胁情境中完成相同任务,发现右侧化优势消失。实验表明类别性空间记忆的行为表现具有右侧化优势,且具有情境不稳定性,这为空间记忆的偏侧化研究提供了一定的行为实验证据。     

Cognitive and AI models of reasoning

Although relatively few in number, cognitive neuroscience studies of reasoning have two general implications for cognitive theories of deduction. First, an important distinction among these theories is whether they focus on the effect of personally relevant content on the processes and representations underlying deductive reasoning. Evidence is reviewed indicating that there is a neuroanatomical basis for both content-independent and content-dependent theories of deduction. Clinical and neuroimaging studies appear to show that content-independent reasoning is mediated by the left hemisphere, whereas content-dependent reasoning is mediated by regions in the right hemisphere and the bilateral ventromedial frontal cortex. In normal subjects, reasoning is likely to be based on contributions from both hemispheres. Second, clinical evidence indicates that the visuospatial processes used in deductive reasoning are mediated by the posterior areas of the left hemisphere, and that verbal and visuospatial reasoning representations overlap at the neuroanatomical level. This finding weighs against the claims of mental-model theory that deduction involves a significant nonverbal component. Further investigation, particularly with contemporary neuroimaging methods, is needed to test these preliminary conclusions.     

Evidence for right hemisphere phonology in a backward masking task

The extent to which orthographic and phonological processes are available during the initial moments of word recognition within each hemisphere is under specified, particularly for the right hemisphere. Few studies have investigated whether each hemisphere uses orthography and phonology under constraints that restrict the viewing time of words and reduce overt phonological demands. The current study used backward masking in the divided visual field paradigm to explore hemisphere differences in the availability of orthographic and phonological word recognition processes. A 20 ms and 60 ms SOA were used to track the time course of how these processes develop during pre-lexical moments of word recognition. Nonword masks varied in similarity to the target words such that there were four types: orthographically and phonologically similar, orthographically but not phonologically similar, phonologically but not orthographically similar and unrelated. The results showed the left hemisphere has access to both orthography and phonology early in the word recognition process. With more time to process the stimulus, the left hemisphere is able to use phonology which benefits word recognition to a larger extent than orthography. The right hemisphere also demonstrates access to both orthography and phonology in the initial moments of word recognition, however, orthographic similarity improves word recognition to a greater extent than phonological similarity.     

Neural dissociation of phonological and visual attention span disorders in developmental dyslexia: FMRI evidence from two case reports

A dissociation between phonological and visual attention (VA) span disorders has been reported in dyslexic children. This study investigates whether this cognitively-based dissociation has a neurobiological counterpart through the investigation of two cases of developmental dyslexia. LL showed a phonological disorder but preserved VA span whereas FG exhibited the reverse pattern. During a phonological rhyme judgement task, LL showed decreased activation of the left inferior frontal gyrus whereas this region was activated at the level of the controls in FG. Conversely, during a visual categorization task, FG demonstrated decreased activation of the parietal lobules whereas these regions were activated in LL as in the controls. These contrasted patterns of brain activation thus mirror the cognitive disorders’ dissociation. These findings provide the first evidence for an association between distinct brain mechanisms and distinct cognitive deficits in developmental dyslexia, emphasizing the importance of taking into account the heterogeneity of the reading disorder.     

Cognition is cool: Can hemispheric activation be assessed by tympanic membrane thermometry?

Hemispheric activation during cognitive tasks using functional magnetic resonance imaging (fMRI) can be difficult to interpret, uncomfortable, and is not widely available. This study investigated whether tympanic membrane thermometry could be used as a broad measure of hemispheric activation. Infrared probes measured ear temperature continuously while subjects performed left or right hemisphere tasks. Temperature decreased in the left ear as activation increased in the left hemisphere during a verbal task, and in the right ear during a visuo-spatial task. When compared to a baseline, ear temperature measurements appeared to reflect relative changes in activation of the left and right hemispheres. Tympanic membrane thermometry therefore may be used as a broad marker of hemispheric activation. Its ability to demonstrate relative involvement of the two hemispheres during cognitive processes makes it especially useful in studies of hemispheric interaction. Its low cost, rapid set-up, and non-invasive nature also make it particularly attractive.     

Right hemisphere participation in reading

This study examined whether the right hemisphere's contribution to lexical semantic processing is greatest when it is "disinhibited." Skilled reading may require the controlled modulation of interhemispheric interaction: the left hemisphere (or some other control mechanism) may regulate the subprocesses of reading by selectively "inhibiting" and "disinhibiting" right hemisphere function. Right-handed undergraduates concurrently performed two tasks: a lateralized semantic or rhyme task and a verbal memory task. It was hypothesized that right hemisphere reading processes would be disinhibited when the left hemisphere was "occupied" with the memory task. This hypothesis was supported for a subgroup of subjects who showed evidence of inhibition of right hemisphere function (i.e., left hemisphere dominance for lexical processing) when the lateralized semantic task was performed alone. Across subjects, there was a strong correlation between the degree of left hemisphere dominance in the single-task semantic conditions and the degree of disinhibition of right hemisphere function in the dual-task semantic condition.     

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.     

偏侧化颜色范畴知觉不依赖于语言?

本研究探讨了偏左脑颜色范畴知觉依赖于语言还是范畴。三组被试分别完成无干扰、语言加工干扰和范畴加工干扰视觉搜索任务。结果发现：无干扰组、语言加工干扰组和范畴加工干扰组的视觉搜索任务中分别出现了偏左脑颜色范畴知觉、左脑劣势颜色范畴知觉和无偏侧化颜色范畴知觉。此结果表明,偏左脑颜色范畴知觉可能主要是语言范畴作为一种范畴对颜色知觉的影响效应,但语言范畴的语言属性也会对颜色知觉产生影响。     

Temporal discrimination in the split brain

Divided visual field studies of neurologically normal adults indicate that the left hemisphere is superior to the right in making temporal judgments. Some neuroimaging and neuropsychological studies, however, have suggested a role for the right hemisphere in temporal processing. We tested the divided hemispheres of a split-brain patient in two tasks requiring temporal judgments about visually presented stimuli. In one task, the patient judged whether two circles presented to one visual field appeared for the same or different durations. In the second task, the patient judged whether the temporal gaps in two circles occurred simultaneously or sequentially. In both tasks, the performance of the right hemisphere was superior to that of the left. This suggests that the right hemisphere plays an important role in making temporal judgments about visually presented stimuli.     

The angular gyrus in developmental dyslexia: task-specific differences in functional connectivity within posterior cortex

Converging evidence from neuroimaging studies of developmental dyslexia reveals dysfunction at posterior brain regions centered in and around the angular gyrus in the left hemisphere. We examined functional connectivity (covariance) between the angular gyrus and related occipital and temporal lobe sites, across a series of print tasks that systematically varied demands on phonological assembly. Results indicate that for dyslexic readers a disruption in functional connectivity in the language-dominant left hemisphere is confined to those tasks that make explicit demands on assembly. In contrast, on print tasks that do not require phonological assembly, functional connectivity is strong for both dyslexic and nonimpaired readers. The findings support the view that neurobiological anomalies in developmental dyslexia are largely confined to the phonological-processing domain. In addition, the findings suggest that right-hemisphere posterior regions serve a compensatory role in mediating phonological performance in dyslexic readers.     

Divided attention years after severe closed head injury: the effect of dependencies between the subtasks

Lesions of white matter which connects distant brain areas are characteristic for closed head injury (CHI). It was predicted that this impairs divided attention only if dependent subtasks are used which require communication between corresponding brain processes. Fourteen chronic severe CHI patients (mean age 42 years) and 14 healthy controls, matched on age, gender, and education, participated in an experiment on divided attention. A typical left hemisphere task and a typical right hemisphere task must be simultaneously performed in a condition where they are completely independent and in conditions with dependencies between the tasks. Only in the dependent conditions the CHI group showed poor divided attention performance.     

Hemisphere-dependent holistic processing of familiar faces

In two behavioral experiments involving lateralized stimulus presentation, we tested whether one of the most commonly used measures of holistic face processing—the composite face effect—would be more pronounced for stimuli presented to the right as compared to the left hemisphere. In experiment 1, we investigated the composite face effect in a verbal identification task, similar to its original report (Young, Hellawell, & Hay, 1987). Aligning top and bottom halves of composite face stimuli led to performance decreases irrespective of hemifield, indicating holistic processing of comparable magnitude for inputs provided separately to either hemisphere. However, when matching of the same top parts was required in experiment 2, an alignment-dependent performance decrease was found for stimuli presented in the left, but not right visual field. These observations suggest that the right hemisphere dominates in early stages of holistic processing, as indexed by the composite face effect, but that later processes such as face identification and naming are based on unified representations that are independent of input lateralization. Moreover, the composite face effect may not rely on the exact same representation(s) when measured in matching and identification tasks.     

Gender differences in empathy: the role of the right hemisphere

The relationship between activation of the right cerebral hemisphere (RH) and empathy was investigated. Twenty-two men and 73 women participated by completing a chimeric face task and empathy questionnaire. For the face task, participants were asked to pick which of the two chimeric faces looked happier. Both men and women were significantly more likely to say the chimera with the smile to their left was happier, suggesting activation of the RH. As expected, men scored significantly lower than women on the empathy questionnaire, p = .003. A correlation was found between RH activation on the face task and empathy for women only, p = .037, suggesting a possible neural basis for gender differences in empathy.     

On the other hand am I rational? Hemispheric activation and the framing effect

In recent decades the investigation of framing effects has become the foremost studied phenomenon of rational/irrational decision making. Two experiments were conducted to determine whether the functional specializations of the left and the right hemispheres would produce different responses to a traditional framing task. In Experiment 1, a behavioral task of finger tapping was used to induce asymmetrical activation of the respective hemispheres. In Experiment 2, a monaural listening procedure was used. In both experiments, the predicted results were found. Framing effects were found when the right hemisphere was selectively activated whereas they were not observed when the left hemisphere was selectively activated. The results are interpreted in light of a dual-processing approach of decision-making.     

The direction of hemispheric asymmetries for object categorization at different levels of abstraction depends on the task

In this study hemispheric asymmetries for categorizing objects at the basic versus subordinate level of abstraction were investigated. As predictions derived from different theoretical approaches are contradictory and experimental evidence is inconclusive in this regard, we conducted two categorization experiments, where we contrasted two experimental paradigms. In the first experiment, subjects had to verify whether a word and a laterally presented picture matched or not. In the second experiment, subjects had to identify laterally presented pictures of animals either at the basic or subordinate level by pressing a corresponding response key. Whereas the first experiment revealed an advantage of the left hemisphere (LH) for categorizing objects at the basic level and of the right hemisphere (RH) for categorizing at the subordinate level, just the opposite brain asymmetry was found in the second experiment. As the stimuli were identical in both experiments, hemispheric asymmetries seem to be strongly task dependent.     

Sex differences in verbal skills: Use of spelling-sound and lexical information

An experiment is described in which possible sex differences in lexical and phonological skills were investigated. A spelling test was used which could not be done on a phonological basis alone and which entailed lexical access for good performance. Women were judged on the evidence for this task to have better lexical ability than men, but no difference was found on a task designed to tap knowledge and use of phonological information in the form of spelling-sound correspondences.