Talma Hendler

Visuo-haptic object-related activation in the ventral visual pathway

The ventral pathway is involved in primate visual object recognition. In humans, a central stage in this pathway is an occipito–temporal region termed the lateral occipital complex (LOC), which is preferentially activated by visual objects compared to scrambled images or textures. However, objects have characteristic attributes (such as three-dimensional shape) that can be perceived both visually and haptically. Therefore, object-related brain areas may hold a representation of objects in both modalities. Using fMRI to map object-related brain regions, we found robust and consistent somatosensory activation in the occipito–temporal cortex. This region showed clear preference for objects compared to textures in both modalities. Most somatosensory object-selective voxels overlapped a part of the visual object-related region LOC. Thus, we suggest that neuronal populations in the occipito–temporal cortex may constitute a multimodal object-related network.

Center-periphery organization of human object areas.

The organizing principles that govern the layout of human object-related areas are largely unknown. Here we propose a new organizing principle in which object representations are arranged according to a central versus peripheral visual field bias. The proposal is based on the finding that building-related regions overlap periphery-biased visual field representations, whereas face-related regions are associated with center-biased representations. Furthermore, the eccentricity maps encompass essentially the entire extent of object-related occipito-temporal cortex, indicating that most object representations are organized with respect to retinal eccentricity. A control experiment ruled out the possibility that the results are due exclusively to unequal feature distribution in these images. We hypothesize that brain regions representing object categories that rely on detailed central scrutiny (such as faces) are more strongly associated with processing of central information, compared to representations of objects that may be recognized by more peripheral information (such as buildings or scenes).

Eccentricity Bias as an Organizing Principle for Human High-Order Object Areas

We have recently proposed a center-periphery organization based on resolution needs, in which objects engaging in recognition processes requiring central-vision (e.g., face-related) are associated with center-biased representations, while objects requiring large-scale feature integration (e.g., buildings) are associated with periphery-biased representations. Here we tested this hypothesis by comparing the center-periphery organization with activations to five object categories: faces, buildings, tools, letter strings, and words. We found that faces, letter strings, and words were mapped preferentially within the center-biased representation. Faces showed a hemispheric lateralization opposite to that of letter strings and words. In contrast, buildings were mapped mainly to the periphery-biased representation, while tools activated both central and peripheral representations. The results are compatible with the notion that center-periphery organization allows the optimal allocation of cortical magnification to the specific requirements of various recognition processes.

An fMRI investigation of the neural correlates underlying the processing of novel metaphoric expressions

The neural networks associated with processing related pairs of words forming literal, novel, and conventional metaphorical expressions and unrelated pairs of words were studied in a group of 15 normal adults using fMRI. Subjects read the four types of linguistic expressions and decided which relation exists between the two words (metaphoric, literal, or unrelated). According to the Graded Salience Hypothesis (GSH, ), which predicts a selective RH involvement in the processing of novel, nonsalient meanings, it is primarily the degree of meaning salience of a linguistic expression rather than literality or nonliterality, which modulates the degree of left hemisphere (LH) and right hemisphere (RH) processing of metaphors. In the present study, novel metaphorical expressions represented the nonsalient interpretations, whereas conventional metaphors and literal expressions represented the salient interpretations. A direct comparison of the novel metaphors vs. the conventional metaphors revealed significantly stronger activity in right posterior superior temporal sulcus, right inferior frontal gyrus, and left middle frontal gyrus. These results support the GSH and suggest a special role for the RH in processing novel metaphors. Furthermore, the right PSTS may be selectively involved in verbal creativity.

Accelerated maturation of white matter in young children with autism: A high b value DWI study

The goal of this work was to study white matter maturation in young children with autism following previous reports of increased cerebral volume during early development, as well as arguments for abnormal neural growth patterns and regulation at this critical developmental period. We applied diffusion tensor imaging (DTI) and high b value diffusion-weighted imaging (DWI) to young children diagnosed with autism and to a typically developing (TD) control group. Fractional anisotropy (FA), probability and displacement were measured in overall analysis as well as in regions of interest (ROI). Individual data points of children with autism were compared to the developmental curves obtained from typically developing children. Increased restriction, reflected in significantly increased FA and probability along with reduced displacement values, was detected in overall analysis as well as in several brain regions. Increased restriction, suggesting an early and accelerated abnormal maturation of white matter, was more dominant in the left hemisphere and was mainly detected in the frontal lobe. No changes were detected in the occipital lobes. These results support previous claims of abnormal brain overgrowth in young children with autism and are in contrast to the decreased restricted diffusion reported in previous studies in adolescent with autism.

Are numbers special? The comparison systems of the human brain investigated by fMRI.

Many studies have suggested that the intraparietal sulcus (IPS), particularly in the dominant hemisphere, is crucially involved in numerical comparisons. However, this parietal structure has been found to be involved in other tasks that require spatial processing or visuospatial attention as well. fMRI was used to investigate three different magnitude comparisons in an event-related-block design: (a) Which digit is larger in numerical value (e.g., 2 or 5)? (b) Which digit is brighter (e.g., 3 or 3)? (c) Which digit is physically larger (e.g., 3 or 3)? Results indicate a widespread cortical network including a bilateral activation of the intraparietal sulci for all different comparisons. However, by computing contrasts of brain activation between the respective comparison conditions and applying a cortical distance effect as an additional criterion, number-specific activation was revealed in left IPS and right temporal regions. These results indicate that there are both commonalities and differences in the spatial layout of the brain systems for numerical and physical comparisons and that especially the left IPS, while involved in magnitude comparison in general, plays a special role in number comparison.

The Neural Reality of Syntactic Transformations Evidence From Functional Magnetic Resonance Imaging

The functional anatomy of syntactic transformations, a major computational operation invoked in sentence processing, was identified through a functional magnetic resonance imaging investigation. A grammaticality judgment task was used, presented through a novel hidden-blocks design. Subjects listened to transformational and non-transformational sentences in which a host of other complexity generators (number of words, prepositions, embeddings, etc.) were kept constant. A series of analyses revealed that the neural processing of transformations is localizable, evoking a highly lateralized and localized activation in the left inferior frontal gyrus (Brocas region) and bilateral activation in the posterior superior temporal sulcus. The pattern of activation associated with transformational analysis was distinct from the one observed in neighboring regions, and anatomically separable from the effects of verb complexity, which yielded significant activation in the left posterior superior temporal sulcus. Taken together with neuropsychological evidence, these results uncover the neural reality of syntactic transformations.

High b-Value q-Space Analyzed Diffusion-Weighted MRI: Application to Multiple Sclerosis

Multiple sclerosis (MS) is an inflammatory disease of the central nervous system (CNS) which affects nearly one million people worldwide, leading to a progressive decline of motor and sensory functions, and permanent disability. High b‐value diffusion‐weighted MR images (b of up to 14000 s/mm2) were acquired from the brains of controls and MS patients. These diffusion MR images, in which signal decay is not monoexponential, were analyzed using the q‐space approach that emphasizes the diffusion characteristics of the slow‐diffusing component. From this analysis, displacement and probability maps were constructed. The computed q‐space analyzed MR images that were compared with conventional T1, T2 (fluid attenuated inversion recovery (FLAIR)), and diffusion tensor imaging (DTI) images were found to be sensitive to the pathophysiological state of white matter. The indices used to construct this q‐space analyzed MR maps, provided a pronounced differentiation between normal tissue and tissues classified as MS plaques by the FLAIR images. More importantly, a pronounced differentiation was also observed between tissues classified by the FLAIR MR images as normal‐appearing white matter (NAWM) in the MS brains, which are known to be abnormal, and the respective control tissues. The potential diagnostic capacity of high b‐value diffusion q‐space analyzed MR images is discussed, and experimental data that explains the consequences of using the q‐space approach once the short pulse gradient approximation is violated are presented. Magn Reson Med 47:115–126, 2002.

The role of the right hemisphere in processing nonsalient metaphorical meanings: Application of Principal Components Analysis to fMRI data

Some researches indicate that the right hemisphere (RH) has a unique role in comprehending the figurative meaning of metaphors whereas the results of other studies do not support the notion of a selective role for the RH in accessing metaphorical meanings. The present research used fMRI technology to test a theoretical explanation of the above conflicting findings. This theoretical account is derived from the Graded Salience Hypothesis (GSH) [Giora, R. (1997). Understanding figurative and literal language: the Graded Salience Hypothesis. Cognitive Linguistics, 7, 183-206; Giora, R. (2003). On our mind: Salience, context and figurative language. New York: Oxford University Press], according to which the degree of meaning salience, rather than literality or nonliterality primarily affects differences between the LH and RH in linguistic processing. Thus, the GSH predicts a selective RH involvement in comprehension of novel, nonsalient metaphoric meanings and LH involvement in the comprehension of conventional, salient metaphoric meanings. Fifteen normal adults participated in a block designed fMRI experiment that compared the patterns of brain activation induced by processing the meanings of literal, conventional metaphoric, novel metaphoric and unrelated word pairs. The subjects performed a semantic judgment task. We applied the Principal Components Analysis (PCA) technique in order to find different functional networks corresponding to the different stimuli. Our results, obtained from PCA of the fMRI data indicate that the right homologue of Wernickes area has a special role in processing novel metaphors. We suggest that a unique network, consisting of the right homologue of Wernickes area, right and left premotor areas, right and left insula and Brocas area, is recruited for the processing of novel metaphors but not for the processing of conventional metaphors.

Characterization of displaced white matter by brain tumors using combined DTI and fMRI.

In vivo white matter tractography by diffusion tensor imaging (DTI) has become a popular tool for investigation of white matter architecture in the normal brain. Despite some unresolved issues regarding the accuracy of DTI, recent studies applied DTI for delineating white matter organization in the vicinity of brain lesions and especially brain tumors. Apart from the intrinsic limitations of DTI, the tracking of fibers in the vicinity or within lesions is further complicated due to changes in diseased tissue such as elevated water content (edema), tissue compression and degeneration. These changes deform the architecture of the white matter and in some cases prevent definite selection of the seed region of interest (ROI) from which fiber tracking begins. We show here that for displaced fiber systems, the use of anatomical approach for seed ROI selection yields insufficient results. Alternatively, we propose to select the seed points based on functional MRI activations which constrain the subjective seed ROI selection. The results are demonstrated on two major fiber systems: the pyramidal tract and the superior longitudinal fasciculus that connect critical motor and language areas, respectively. The fMRI based seed ROI selection approach enabled a more comprehensive mapping of these fiber systems. Furthermore, this procedure enabled the characterization of displaced white matter using the eigenvalue decomposition of DTI. We show that along the compressed fiber system, the diffusivity parallel to the fiber increases, while that perpendicular to the fibers decreases, leading to an overall increase in the fractional anisotropy index reflecting the compression of the fiber bundle. We conclude that definition of the functional network of a subject with deformed white matter should be done carefully. With fMRI, one can more accurately define the seed ROI for DTI based tractography and to provide a more comprehensive, functionally related, white matter mapping, a very important tool used in pre-surgical mapping.