Left Ventral Occipitotemporal Cortex Research Articles

How Does Learning to Read Affect Speech Perception?

Behavioral studies have demonstrated that learning to read and write affects the processing of spoken language. The present study investigates the neural mechanism underlying the emergence of such orthographic effects during speech processing. Transcranial magnetic stimulation (TMS) was used to tease apart two competing hypotheses that consider this orthographic influence to be either a consequence of a change in the nature of the phonological representations during literacy acquisition or a consequence of online coactivation of the orthographic and phonological representations during speech processing. Participants performed an auditory lexical decision task in which the orthographic consistency of spoken words was manipulated and repetitive TMS was used to interfere with either phonological or orthographic processing by stimulating left supramarginal gyrus (SMG) or left ventral occipitotemporal cortex (vOTC), respectively. The advantage for consistently spelled words was removed only when the stimulation was delivered to SMG and not to vOTC, providing strong evidence that this effect arises at a phonological, rather than an orthographic, level. We propose a possible mechanistic explanation for the role of SMG in phonological processing and how this is affected by learning to read.

Automatic Top-Down Processing Explains Common Left Occipito-Temporal Responses to Visual Words and Objects

Previous studies have demonstrated that a region in the left ventral occipito-temporal (LvOT) cortex is highly selective to the visual forms of written words and objects relative to closely matched visual stimuli. Here, we investigated why LvOT activation is not higher for reading than picture naming even though written words and pictures of objects have grossly different visual forms. To compare neuronal responses for words and pictures within the same LvOT area, we used functional magnetic resonance imaging adaptation and instructed participants to name target stimuli that followed briefly presented masked primes that were either presented in the same stimulus type as the target (word–word, picture–picture) or a different stimulus type (picture–word, word–picture). We found that activation throughout posterior and anterior parts of LvOT was reduced when the prime had the same name/response as the target irrespective of whether the prime-target relationship was within or between stimulus type. As posterior LvOT is a visual form processing area, and there was no visual form similarity between different stimulus types, we suggest that our results indicate automatic top-down influences from pictures to words and words to pictures. This novel perspective motivates further investigation of the functional properties of this intriguing region.

Functional dissociation of the left ventral occipito-temporal cortex in the direct and indirect retrieval of color features

Previous studies suggest that the storage/retrieval of object features is related to brain regions that are involved in the processing of these features. However, it remains unclear whether, and under what conditions, retrieving information about a feature reactivates the same region that specifically supports that feature’s perception. In this functional magnetic resonance imaging (fMRI) study, we compared brain activation in the left ventral occipito-temporal cortex during subjects performing a color perception task, and direct and indirect color retrieval tasks. After performing the color perception task to localize the regions responsible for color perception, subjects were intensively trained (outside of the scanner) to remember associations between colors and motion directions, and associations between colors and letters. Then, they were asked to perform two color retrieval tasks in the scanner, with stationary and gray scaled images as control stimuli. The results showed that the bilateral posterior occipito-temporal cortex was activated during the color perception task. When color information was retrieved by direct cues (motion direction), the same bilateral occipito-temporal region was activated. When color information was retrieved indirectly (judging whether a motion direction matched a letter by their associated colors), a region anterior to the color perception region in the left ventral occipito-temporal cortex was additionally activated. Our results provided evidence for the functional dissociation in the two subregions of the ventral occipito-temporal cortex during retrieval of color features: the posterior area might relate to perceptual features of color, while the anterior region might relate to the knowledge of associations with color.

The Left Ventral Occipito-Temporal Response to Words Depends on Language Lateralization but Not on Visual Familiarity

The sensitivity of the left ventral occipito-temporal (vOT) cortex to visual word processing has triggered a considerable debate about the role of this region in reading. One popular view is that the left vOT underlies the perceptual expertise needed for rapid skilled reading. Because skilled reading breaks down when words are presented in a visually unfamiliar format, we tested this hypothesis by analyzing vOT responses to horizontally presented words (familiar format) and vertically presented words (unfamiliar format). In addition, we compared the activity in participants with left and right cerebral dominance for language generation. Our results revealed 1) that the vOT activity during reading is lateralized to the same side as the inferior frontal activity during word generation, 2) that vertically and horizontally presented words triggered the same amount of activity in the vOT of the dominant hemisphere, but 3) that there was significantly more activity for vertically presented words in the vOT of the nondominant hemisphere. We suggest that the reading-related activity in vOT reflects the integration of general perceptual processes with language processing in the anterior brain regions and is not limited to skilled reading in the familiar horizontal format.

Evidence for Highly Selective Neuronal Tuning to Whole Words in the “Visual Word Form Area”

Theories of reading have posited the existence of a neural representation coding for whole real words (i.e., an orthographic lexicon), but experimental support for such a representation has proved elusive. Using fMRI rapid adaptation techniques, we provide evidence that the human left ventral occipitotemporal cortex (specifically the "visual word form area," VWFA) contains a representation based on neurons highly selective for individual real words, in contrast to current theories that posit a sublexical representation in the VWFA.

Sensitivity to orthographic familiarity in the occipito-temporal region

The involvement of the left hemisphere occipito-temporal (OT) junction in reading has been established, yet there is current controversy over the region's specificity for reading and the nature of its role in the reading process. Recent neuroimaging findings suggest that the region is sensitive to orthographic familiarity [Kronbichler, M., Bergmann, J., Hutzler, F., Staffen, W., Mair, A., Ladurner, G., Wimmer, H. 2007. Taxi vs. Taksi: on orthographic word recognition in the left ventral occipito-temporal cortex. Journal of Cognitive Neuroscience 19, 1–11], and the present study tested that hypothesis. Using fMRI, the OT region and other regions in the reading network were localized in 28 adult, right-handed participants. The BOLD signal in these regions was measured during a phonological judgment task (i.e., “Does it sound like a word?”). Stimuli included words, pseudohomophones (phonologically familiar yet orthographically unfamiliar), and pseudowords (phonologically and orthographically unfamiliar) that were matched on lexical properties including sublexical orthography. Relative to baseline, BOLD signal in the OT region was greater for pseudohomophones than for words, suggesting that the region is sensitive to orthographic familiarity at the whole-word level. Further contrasts of orthographic frequency within the word condition revealed increased BOLD signal for low- than high-frequency words. Specialization in the OT region for recognition of frequent letter strings may support the development of reading expertise. Additionally, BOLD signal in the OT region correlates positively with reading efficiency, supporting the idea that this region is a skill zone for reading printed words. BOLD signal in the IFG and STG correlates negatively with reading efficiency, indicating that processing effort in these classic phonological regions is inversely related to reading efficiency.

Multiple brain networks for visual self-recognition with different sensitivity for motion and body part

Multiple brain networks may support visual self-recognition. It has been hypothesized that the left ventral occipito-temporal cortex processes one's own face as a symbol, and the right parieto-frontal network processes self-image in association with motion–action contingency. Using functional magnetic resonance imaging, we first tested these hypotheses based on the prediction that these networks preferentially respond to a static self-face and to moving one's whole body, respectively. Brain activation specifically related to self-image during familiarity judgment was compared across four stimulus conditions comprising a two factorial design: factor Motion contrasted picture (Picture) and movie (Movie), and factor Body part a face (Face) and whole body (Body). Second, we attempted to segregate self-specific networks using a principal component analysis (PCA), assuming an independent pattern of inter-subject variability in activation over the four stimulus conditions in each network. The bilateral ventral occipito-temporal and the right parietal and frontal cortices exhibited self-specific activation. The left ventral occipito-temporal cortex exhibited greater self-specific activation for Face than for Body, in Picture, consistent with the prediction for this region. The activation profiles of the right parietal and frontal cortices did not show preference for Movie Body predicted by the assumed roles of these regions. The PCA extracted two cortical networks, one with its peaks in the right posterior, and another in frontal cortices; their possible roles in visuo-spatial and conceptual self-representations, respectively, were suggested by previous findings. The results thus supported and provided evidence of multiple brain networks for visual self-recognition.

Phonological decoding involves left posterior fusiform gyrus

Aloud reading of novel words is achieved by phonological decoding, a process in which grapheme-to-phoneme conversion rules are applied to "sound out" a word's spoken representation. Numerous brain imaging studies have examined the neural bases of phonological decoding by contrasting pseudoword (pronounceable nonwords) to real word reading. However, only a few investigations have examined pseudoword reading under both aloud and silent conditions, task parameters that are likely to significantly alter the functional anatomy of phonological decoding. Subjects participated in an fMRI study of aloud pseudoword, aloud real word, silent pseudoword, and silent real word reading. Using this two-by-two design, we examined effects of word-type (real words vs. pseudowords) and response-modality (silent vs. aloud) and their interactions. We found 1) four regions to be invariantly active across the four reading conditions: the anterior aspect of the left precentral gyrus (Brodmann's Area (BA) 6), and three areas within the left ventral occipitotemporal cortex; 2) a main effect of word-type (pseudowords > words) in left inferior frontal gyrus and left intraparietal sulcus; 3) a main effect of response-modality (aloud > silent) that included bilateral motor, auditory, and extrastriate cortex; and 4) a single left hemisphere extrastriate region showing a word-type by response-modality interaction effect. This region, within the posterior fusiform cortex at BA 19, was uniquely modulated by varying phonological processing demands. This result suggests that when reading, word forms are subject to phonological analysis at the point they are first recognized as alphabetic stimuli and BA 19 is involved in processing the phonological properties of words.

Regional brain gray matter volume differences in patients with bipolar disorder as assessed by optimized voxel-based morphometry

BackgroundStructural magnetic resonance imaging (MRI) studies of regions of interest in brain have been inconsistent in demonstrating volumetric differences in subjects with bipolar disorder (BD). Voxel-based morphometry (VBM) provides an unbiased survey of the brain, can identify novel brain areas, and validates previously hypothesized regions. We conducted both optimized VBM, comparing MRI gray matter volume, and traditional VBM, comparing MRI gray matter density, in 11 BD subjects and 31 healthy volunteers. To our knowledge, these are the first VBM analyses of BD. MethodsSegmented MRI gray matter images were normalized into standardized stereotactic space, modulated to allow volumetric analysis (optimized only), smoothed, and compared at the voxel level with statistical parametric mapping. ResultsOptimized VBM showed that BD subjects had smaller volume in left ventromedial temporal cortex and bilateral cingulate cortex and larger volume in left insular/frontoparietal operculum cortex and left ventral occipitotemporal cortex. Traditional VBM showed that BD subjects had less gray matter density in left ventromedial temporal cortex and greater gray matter density in left insular/frontoparietal operculum cortex and bilateral thalamic cortex. Exploratory analyses suggest that these abnormalities might differ according to gender. ConclusionsBipolar disorder is associated with volumetric and gray matter density changes that involve brain regions hypothesized to influence mood.

Three Distinct Ventral Occipitotemporal Regions for Reading and Object Naming

This study investigates word and object processing during naming and viewing tasks and identifies three distinct regions in the left ventral occipitotemporal cortex. Irrespective of task, words and objects (relative to meaningless visual controls) activated the medial surface of the left anterior fusiform gyrus, a region that has previously been associated with semantic knowledge. A more lateral region was differentially active for naming words and objects relative to viewing the same stimuli and a more posterior region was differentially active for objects relative to words irrespective of task. In addition, we found that word processing resulted in greater activation than object processing on the dorsal surface of the left superior temporal gyrus and the left supramarginal gyrus. These regions appear to be important for converting orthography into phonology; their response to words irrespective of task is consistent with established psychological evidence that implicit phonological processing is stronger for words than objects.