A multimodal language region in the ventral visual pathway

Neural Response Suppression Predicts Repetition Priming of Spoken Words and Pseudowords

An important method for studying how the brain processes familiar stimuli is to present the same item on more than one occasion and measure how responses change with repetition. Here we use repetition priming in a sparse functional magnetic resonance imaging (fMRI) study to probe the neuroanatomical basis of spoken word recognition and the representations of spoken words that mediate repetition priming effects. Participants made lexical decisions to words and pseudowords spoken by a male or female voice that were presented twice, with half of the repetitions in a different voice. Behavioral and neural priming was observed for both words and pseudowords and was not affected by voice changes. The fMRI data revealed an elevated response to words compared to pseudowords in both posterior and anterior temporal regions, suggesting that both contribute to word recognition. Both reduced and elevated activation for second presentations (repetition suppression and enhancement) were observed in frontal and posterior regions. Correlations between behavioral priming and neural repetition suppression were observed in frontal regions, suggesting that repetition priming effects for spoken words reflect changes within systems involved in generating behavioral responses. Based on the current results, these processes are sufficiently abstract to display priming despite changes in the physical form of the stimulus and operate equivalently for words and pseudowords.

“Scientific roots” of dualism in neuroscience

Although the dualistic concept is unpopular among neuroscientists involved in experimental studies of the brain, neurophysiological literature is full of covert dualistic statements on the possibility of understanding neural mechanisms of human consciousness. Particularly, the covert dualistic attitude is exhibited in the unwillingness to discuss neural mechanisms of consciousness, leaving the problem of consciousness to psychologists and philosophers. This covert dualism seems to be rooted in the main paradigm of neuroscience that suggests that cognitive functions, such as language production and comprehension, face recognition, declarative memory, emotions, etc., are performed by neural networks consisting of simple elements. I argue that neural networks of any complexity consisting of neurons whose function is limited to the generation of electrical potentials and the transmission of signals to other neurons are hardly capable of producing human mental activity, including consciousness. Based on results obtained in physiological, morphological, clinical, and genetic studies of cognitive functions (mainly linguistic ones), I advocate the hypothesis that the performance of cognitive functions is based on complex cooperative activity of "complex" neurons that are carriers of "elementary cognition." The uniqueness of human cognitive functions, which has a genetic basis, is determined by the specificity of genes expressed by these "complex" neurons. The main goal of the review is to show that the identification of the genes implicated in cognitive functions and the understanding of a functional role of their products is a possible way to overcome covert dualism in neuroscience.

The intersubject and intrasubject reproducibility of FMRI activation during three encoding tasks: implications for clinical applications

The goal of the present study was to evaluate the inter- and intrasubject reproducibility of FMRI activation for three memory encoding tasks previously used in the context of presurgical functional mapping. The primary region of interest (ROI) was the medial temporal lobe (MTL). Comparative ROIs included the inferior frontal and fusiform gyri which are less affected by susceptibility-induced signal losses than the MTL regions. Eighteen subjects were scanned using three memory encoding paradigms: word-pair, pattern, and scene encoding. Nine subjects underwent repeat scanning. Intersubject reproducibility of FMRI activation was evaluated by examining the percent of subjects who showed activation within a given ROI and the range to which individual laterality indices (LIs) varied from the mean. Intrasubject test-retest reproducibility was evaluated by examining the LI test-retest correlation, the average difference between LIs from two separate imaging sessions, and concordance ratios of activation volumes (R(volume) and R(overlap)). For scene encoding the reproducibility of activation volume and LIs within the MTL were as good as or better than the reproducibility within the fusiform and inferior frontal ROIs. For pattern encoding and word-pair encoding, the reproducibility of activation volume and LIs within the MTL tended to be worse compared to the fusiform and inferior frontal ROIs. The differences in FMRI reproducibility appeared more dependent on the task than the susceptibility effects. The results of this study suggest that FMRI-based assessment of the neural substrates of memory using a scene encoding task may be a useful clinical tool.

Cognitive and brain mechanisms in sensory substitution of vision: a contribution to the study of human perception

Sensory substitution refers to the use of one sense to pick up information normally gathered by another sensory organ. With recent technological advances and scientific progress, sensory substitution appears as an interesting alternative for restoring some functions of a defective sensory organ (e.g., the sight in case of blindness). At the same time, our knowledge about cognitive and brain mechanisms involved in sensory substitution has grown considerably, bringing new insights into human perception and neural plasticity. From this perspective, sensory substitution can be considered as both a tool to investigate human cognition and brain functions, and a research topic in its own right. This paper addresses some of the major questions raised by sensory substitution, demonstrates how the study of sensory substitution enhances our understanding of human perception and brain plasticity and provides an overview of rehabilitation potentialities.

Cognitive processing in Chinese literate and illiterate subjects: an fMRI study

Functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) were used to map brain activation during language tasks. While previous studies have compared performance between alphabetic literate and illiterate subjects, there have been no such data in Chinese-speaking individuals. In this study, we used fMRI to examine the effects of education on neural activation associated with silent word recognition and silent picture-naming tasks in 24 healthy right-handed Chinese subjects (12 illiterates and 12 literates). There were 30 single Chinese characters in the silent word recognition task and 30 meaningful road-signs in the silent picture-naming task. When we compared literate and illiterate subjects, we observed education-related differences in activation patterns in the left inferior/middle frontal gyrus and both sides of the superior temporal gyrus for the silent word recognition task and in the bilateral inferior/middle frontal gyrus and left limbic cingulated gyrus for the silent picture-naming task. These results indicate that the patterns of neural activation associated with language tasks are strongly influenced by education. Education appears to have enhanced cognitive processing efficiency in language tasks.

Meta-analyzing left hemisphere language areas: phonology, semantics, and sentence processing

The advent of functional neuroimaging has allowed tremendous advances in our understanding of brain-language relationships, in addition to generating substantial empirical data on this subject in the form of thousands of activation peak coordinates reported in a decade of language studies. We performed a large-scale meta-analysis of this literature, aimed at defining the composition of the phonological, semantic, and sentence processing networks in the frontal, temporal, and inferior parietal regions of the left cerebral hemisphere. For each of these language components, activation peaks issued from relevant component-specific contrasts were submitted to a spatial clustering algorithm, which gathered activation peaks on the basis of their relative distance in the MNI space. From a sample of 730 activation peaks extracted from 129 scientific reports selected among 260, we isolated 30 activation clusters, defining the functional fields constituting three distributed networks of frontal and temporal areas and revealing the functional organization of the left hemisphere for language. The functional role of each activation cluster is discussed based on the nature of the tasks in which it was involved. This meta-analysis sheds light on several contemporary issues, notably on the fine-scale functional architecture of the inferior frontal gyrus for phonological and semantic processing, the evidence for an elementary audio-motor loop involved in both comprehension and production of syllables including the primary auditory areas and the motor mouth area, evidence of areas of overlap between phonological and semantic processing, in particular at the location of the selective human voice area that was the seat of partial overlap of the three language components, the evidence of a cortical area in the pars opercularis of the inferior frontal gyrus dedicated to syntactic processing and in the posterior part of the superior temporal gyrus a region selectively activated by sentence and text processing, and the hypothesis that different working memory perception-actions loops are identifiable for the different language components. These results argue for large-scale architecture networks rather than modular organization of language in the left hemisphere.

Aspects of Multisensory Perception: The Integration of Visual and Auditory Information in Musical Experiences

One of the requirements for being a successful musical conductor is to be able to locate sounds instantaneously in time and space. Because this requires the integration of auditory and visual information, the purpose of this study was to examine multisensory processing in conductors and a matched set of control subjects. Subjects participated in a series of behavioral tasks, including pitch discrimination, temporal-order judgment (TOJ), and target localization. Additionally, fMRI scans were done on a subset of subjects who performed a multisensory TOJ task. Analyses of behavioral data indicate that, in the auditory realm, conductors were more accurate in both pitch discrimination and TOJs as well as in locating targets in space. Furthermore, these same subjects also demonstrated a benefit from the combination of auditory and visual information that was not observed in control subjects when locating visual targets. Finally, neural substrates in BA 37, 39/40 were identified as potential areas underlying the conductors' superior multisensory TOJs. Data collection and analyses are ongoing and will lead to an improved understanding of multisensory integration in a complex, musical behavior.

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.

When meaningless symbols become letters: Neural activity change in learning new phonograms

Left fusiform gyrus and left angular gyrus are considered to be respectively involved with visual form processing and associating visual and auditory (phonological) information in reading. However, there are a number of studies that fail to show the contribution of these regions in carrying out these aspects of reading. Considerable differences in the type of stimuli and tasks used in the various studies may account for the discrepancy in results. This functional magnetic resonance imaging (fMRI) study attempts to control aspects of experimental stimuli and tasks to specifically investigate brain regions involved with visual form processing and character-to-phonological (i.e., simple grapheme-to-phonological) conversion processing for single letters. Subjects performed a two-back identification task using known Japanese, and previously unknown Korean, and Thai phonograms before and after training on one of the unknown language orthographies. Japanese subjects learned either five Korean or five Thai phonograms. Brain regions related to visual form processing were assessed by comparing activity related to native (Japanese) phonograms with that of non-native (Korean and Thai) phonograms. There was no significant differential brain activity for visual form processing. Brain regions related to character-to-phonological conversion processing were assessed by comparing pre- and post-tests of trained non-native phonograms with that of native phonograms and non-trained non-native phonograms. Significant differential activation post-relative to pre-training exclusively for the trained non-native phonograms was found in left angular gyrus. In addition, psychophysiologic interaction (PPI) analysis revealed greater integration of left angular gyrus with primary visual cortex as well as with superior temporal gyrus for the trained phonograms post-relative to pre-training. The results suggest that left angular gyrus is involved with character-to-phonological conversion in letter perception.

Conceptual approach for the design of radiology reporting interfaces: the talking template

Within the coming decade, traditional dictation supported by human transcription for radiology reports will be replaced by one or more computerized methods. This paper discusses the cognitive and process efficiency problems arising from currently available technology including speech recognition and menu-driven interfaces. A specific concept for interaction with the reporting interface is proposed. This is called the "talking template" and departs from other designs by providing for all interactions to be mediated through audible prompts and microphone controls. The radiologist can recapture efficiency and cognitive focus by dictating while viewing images without the "look away" problem inherent in other interfaces.

Use of time differences in normal hearing – cortical processing of promontorial stimuli

To test the hypothesis that ability to discriminate small duration differences is positively correlated with activity in the right temporal lobe, we used positron emission tomography in six normally hearing subjects, stimulated via the promontory in a procedure that mimics the auditory nerve stimulation with a cochlear implant. Stimulus consisted of electrical bursts, and tasks included gap detection and temporal difference limen (TDL). TDL is a measure of discriminatory processing of sound duration in cochlear implant candidates, demonstrated to predict outcome. Good speech perception after cochlear implantation is associated with activity in right temporal areas. Although perceived variably by the subjects, the stimulus itself activated bilateral secondary somatosensory cortex, suggesting differential stimulation of multiple sensory modalities. Only TDL raised blood flow in both posterior middle temporal gyri (MTG) and the right prefrontal cortex. As the right posterior MTG is known to be active during duration discrimination of different modalities and in the perception of words containing manipulated phonemes, we conclude that recruitment of this part of the right hemisphere is important to the comprehension of speech containing mostly temporal cues. The study shows that stimulus-induced activation reflects the goal of the task rather than the nature of the stimulus.

Subliminal Convergence of Kanji and Kana Words: Further Evidence for Functional Parcellation of the Posterior Temporal Cortex in Visual Word Perception

Recent evidence has suggested that the human occipito-temporal region comprises several subregions, each sensitive to a distinct processing level of visual words. To further explore the functional architecture of visual word recognition, we employed a subliminal priming method with functional magnetic resonance imaging (fMRI) during semantic judgments of words presented in two different Japanese scripts, Kanji and Kana. Each target word was preceded by a subliminal presentation of either the same or a different word, and in the same or a different script. Behaviorally, word repetition produced significant priming regardless of whether the words were presented in the same or different script. At the neural level, this cross-script priming was associated with repetition suppression in the left inferior temporal cortex anterior and dorsal to the visual word form area hypothesized for alphabetical writing systems, suggesting that cross-script convergence occurred at a semantic level. fMRI also evidenced a shared visual occipito-temporal activation for words in the two scripts, with slightly more mesial and right-predominant activation for Kanji and with greater occipital activation for Kana. These results thus allow us to separate script-specific and script-independent regions in the posterior temporal lobe, while demonstrating that both can be activated subliminally.

Automatic word form processing in masked priming: An ERP study

Five prime types (unrelated words, pronounceable nonwords, illegal strings of letters, false fonts, or neutral strings of Xs) preceded word and nonword targets in a masked priming study designed to investigate word form processing as indexed by event-related potentials (ERPs). Participants performed a lexical decision task on targets. In the 150-250-ms epoch at fronto-central, central, and temporo-parietal sites ERPs were smallest to targets preceded by words and nonwords, followed by letter strings, false fonts, and finally neutral primes. This refractory pattern sensitive to orthography supports the view that ERPs in the 150-250-ms epoch index activation of neural systems involved in word form processing and suggests that such activation may be graded, being maximal with word-like stimuli and relatively reduced with alphabet-like stimuli. Further, these results from a masked priming paradigm confirm the automatic nature of word form processing.

Hippocampus activity differentiates good from poor learners of a novel lexicon

Language proficiency is a key to academic and workplace success for native and non-native speakers. It is largely unknown, however, why some people pick up languages more easily than others. We used event-related functional magnetic resonance imaging (e-fMRI) to elucidate which brain regions are modulated during the acquisition of a novel lexicon and which of these learning-related activity changes correlated with general semantic language knowledge. Fourteen healthy young subjects learned a novel vocabulary of 45 concrete nouns via an associative learning principle over the course of five blocks during e-fMRI. As a control condition, subjects took part in a structurally identical "No-Learning" condition lacking any learning principle. Overall, increasing vocabulary proficiency was associated with (intercorrelated) modulations of activity within the left hippocampus and the left fusiform gyrus, regions involved in the binding and integration of multimodal stimuli, and with an increasing activation of the left inferior parietal cortex, the presumed neural store of phonological associations. None of these activity changes were observed during the control condition. Furthermore, subjects who showed less suppression of hippocampal activity over learning blocks scored higher on semantic knowledge in their native language and learned the novel vocabulary more efficiently. Our findings indicate that (a) the successful acquisition of a new lexicon depends on correlated amplitude changes between the left hippocampus and neocortical regions and (b) learning-related hippocampus activity is a stable marker of individual differences in the ability to acquire and master vocabularies.

The neural correlate of very-long-term picture priming

Repetition priming denotes a behavioural change caused by prior exposure to a stimulus. The effect is known to last for weeks. This study addresses the underlying neural mechanisms for very-long-term picture priming by using event-related functional magnetic resonance imaging complemented by a behavioural paradigm. Previous functional imaging studies with shorter retention intervals have shown that priming is associated with changes in the activity of both the occipital and posterior temporal cortex. In this study we compared retention intervals of 1 day and 6 weeks after initial exposure to a picture stimulus. Priming-related decreases in cortical activity in posterior extrastriate and dorsal left inferior frontal areas were found only for the shorter retention interval. In contrast, fMRI activation in the inferior posterior temporal and anterior left inferior frontal cortex was reduced following priming for both retention intervals. In the behavioural paradigm, the priming effect was stable over time. We conclude that the left inferior frontal and inferior posterior temporal cortex play a key role in the very-long-term priming effect.

Renewal of the neurophysiology of language: functional neuroimaging

Functional neuroimaging methods have reached maturity. It is now possible to start to build the foundations of a physiology of language. The remarkable number of neuroimaging studies performed so far illustrates the potential of this approach, which complements the classical knowledge accumulated on aphasia. Here we attempt to characterize the impact of the functional neuroimaging revolution on our understanding of language. Although today considered as neuroimaging techniques, we refer less to electroencephalography and magnetoencephalography studies than to positron emission tomography and functional magnetic resonance imaging studies, which deal more directly with the question of localization and functional neuroanatomy. This review is structured in three parts. 1) Because of their rapid evolution, we address technical and methodological issues to provide an overview of current procedures and sketch out future perspectives. 2) We review a set of significant results acquired in normal adults (the core of functional imaging studies) to provide an overview of language mechanisms in the "standard" brain. Single-word processing is considered in relation to input modalities (visual and auditory input), output modalities (speech and written output), and the involvement of "central" semantic processes before sentence processing and nonstandard language (illiteracy, multilingualism, and sensory deficits) are addressed. 3) We address the influence of plasticity on physiological functions in relation to its main contexts of appearance, i.e., development and brain lesions, to show how functional imaging can allow fine-grained approaches to adaptation, the fundamental property of the brain. In closing, we consider future developments for language research using functional imaging.

V1 activation in congenitally blind humans is associated with episodic retrieval

Recently we showed that the occipital cortex of congenitally blind humans is activated during verbal-memory tasks. Activation was found in regions corresponding to the retinotopic visual areas of sighted humans, including the calcarine sulcus (V1). No such occipital activation was found in sighted humans. One year later, the same blind subjects participated in a second fMRI scan, to study the contribution of semantic elements and episodic memory to the occipital activation. The subjects performed an episodic-memory task, requiring recognition of words that were originally presented in the first scan. We demonstrate here that the magnitude of V1 activation during the recognition task is correlated with memory performance, assessed during the scan. Across the blind, the better-remembered set of words elicited greater V1 activation than words from the poorly-remembered set, although the semantic components and the behavioral task were similar in the two sets. This indicates that on top of semantic processing (suggested previously), V1 activation in the blind is probably associated with long-term episodic memory. Indeed, within the blind, those who showed better recognition-memory performance had greater V1 activation compared with the poorer performers. We conclude that the posterior occipital cortex (including V1) of the congenitally blind is likely to be involved in episodic retrieval.

Visual cortical activity during tactile perception in the sighted and the visually deprived

This article reviews studies demonstrating activity in visual cortex during tactile perception in sighted participants as well as in those who have experienced visual deprivation of varying duration. This field has been very active over the last few years, with the result that a number of exciting findings have emerged, but a unifying framework is still lacking. The first section of this article deals with investigations revealing that visual cortical activity is regularly associated with the neural processing of tactile inputs in normally sighted individuals. Next, the possible reasons underlying such visual cortical recruitment are considered. The focus then shifts to the effects of visual deprivation, examining the involvement of visual cortex in sensory and language processing in the early and late blind. The final section gives an account of studies suggesting that a remarkable degree of plasticity can be observed even after quite short-lasting visual deprivation. Overall, it appears that the nature of visual cortical activity during nonvisual tasks in the sighted can be influenced by late-onset blindness and even by brief interruptions of visual input; however, the relevant neural plasticity seems to considerably more exuberant if vision is lost very early in life or was never present, which suggests that there is a critical period for the maximal expression of such plasticity.

The roles of the “visual word form area” in reading

Activation of the left midfusiform gyrus in response to reading words and pseudowords is such a reliable finding in functional imaging that this region has been called "the visual word form area" (VWFA). However, this label has recently been challenged, because activation in VWFA is also observed in other lexical tasks. We evaluated whether VWFA is necessary, sufficient, or specialized for reading by examining how frequently acute lesions in VWFA disrupt tasks that require access to written word forms versus other lexical tasks. We administered lexical tasks with spoken and written input and output, and identified damage or dysfunction of VWFA and other regions of interest (ROI) on diffusion- and perfusion-weighted imaging (DWI and PWI) in 80 patients within 24 h of onset of acute left ischemic stroke. Associations between abnormalities in each region of interest and impairment on lexical tasks were evaluated with chi-squared tests. Damage or dysfunction of VWFA was not significantly associated with impairment of written word comprehension or lexical decision, but was significantly associated with impairment on all tasks requiring lexical output: oral reading and oral naming (visual or tactile input), and written naming. We account for these results and results from functional imaging by proposing that the left midfusiform gyrus normally has two roles in reading: (1) computation of location- and modality-independent grapheme sequences from written word stimuli, and (2) a modality-independent stage of lexical processing that links modality-specific input and output representations. VWFA is not necessary for the former because the right homologue of VWFA can immediately assume this role.

Neural systems for sign language production: mechanisms supporting lexical selection, phonological encoding, and articulation

Overt production of ASL signs was evaluated using H(2)(15)O PET to differentiate brain systems that support sign language production at the lexical-selection and phonological-articulatory levels. Subjects were 16 right-handed, congenitally deaf native ASL signers (10 women, six men; age 20 to 29 years). Scans were performed while subjects (1) passively viewed ASL nouns, (2) repeated nouns, (3) generated verbs in response to these nouns, (4) passively viewed videotaped segments depicting transitive actions, and (5) generated a verb to describe these actions. Conjunctions between the two verb-generation tasks revealed left-lateralized activation of perisylvian, frontal, and subcortical regions commonly observed in spoken language generation tasks and implicated in processes of semantic feature binding and lexical selection. Analysis of noun repetition minus viewing condition revealed activation of distinct systems supporting phonological encoding and articulation, including bilateral activation of sensorimotor areas and association cortices in the temporal, parietal, and occipital lobes. In addition, lexical-selection and articulatory processes were associated with activation of different corticostriatal-thalamocortical circuits: articulation with activation of the motor, and lexical-selection with activation of the prefrontal circuits, respectively. The results collectively provide insight into dissociable neural systems underlying these psycholinguistic functions. In addition, activation of regions that are typically associated with the auditory system during sign production suggests that these regions may support modality-independent linguistic processes, or may indicate cross-modal plasticity within the deaf brain.

Distinct unimodal and multimodal regions for word processing in the left temporal cortex

How are word recognition circuits organized in the left temporal lobe? We used functional magnetic resonance imaging (fMRI) to dissect cortical word-processing circuits using three diagnostic criteria: the capacity of an area (1) to respond to words in a single modality (visual or auditory) or in both modalities, (2) to modulate its response in a top-down manner as a function of the graphemic or phonemic emphasis of the task, and (3) to show repetition suppression in response to the conscious repetition of the target word within the same sensory modality or across different modalities. The results clarify the organization of visual and auditory word-processing streams. In particular, the visual word form area (VWFA) in the left occipitotemporal sulcus appears strictly as a visual unimodal area. It is, however, bordered by a second lateral inferotemporal area which is multimodal [lateral inferotemporal multimodal area (LIMA)]. Both areas might have been confounded in past work. Our results also suggest a possible homolog of the VWFA in the auditory stream, the auditory word form area, located in the left anterior superior temporal sulcus.

Visual recognition of faces, objects, and words using degraded stimuli: where and when it occurs

We studied time course and cerebral localisation of word, object, and face recognition using event-related potentials (ERPs) and source localisation techniques. To compare activation rates of these three categories, we used degraded images that easily pop out without any change in the physical features of the stimuli, once the meaning is revealed. Comparisons before and after identification show additional periods of activation beginning at 100 msec for faces and at around 200 msec for objects and words. For faces, this activation occurs predominantly in right temporal areas, whereas for objects, the specific time period gives rise to bilateral posterior but right dominant foci. Finally, words show a maximum area of activation in the left temporooccipital area at their specific time period. These results provide unequivocal evidence that when effects of low-level visual features are circumvented, faces, objects, and words are not only distinct in terms of their anatomic routes, but also in terms of their times of processing.

Neural changes associated with speech learning in deaf children following cochlear implantation

Brain plasticity was investigated, which underlies the gaining of auditory sensory and/or auditory language in deaf children with an early onset deafness after cochlear implantation (CI) surgery. This study examined both the glucose metabolism of the brain and the auditory speech learning using 18F-fluorodeoxyglucose positron emission tomography (FDG-PET) and the Central Institute of Deaf (CID) test, respectively, both before and after the CI surgery. In a within analysis comparing the pre-CI and the post-CI PET results, CI itself resulted in an increase in the glucose metabolism in the medial visual cortex, the bilateral thalamus, and the posterior cingulate. Compared with the normal hearing controls, the brain activity of the deaf children was greater in the medial visual cortex and bilateral occipito-parietal junctions after the CI. The better speech perception ability was associated with increases in activity in the higher visual areas such as middle occipito-temporal junction (hMT/V5) and posterior inferior temporal region (BA 21/37) in the left hemisphere and associated with decreases in activity in the right inferior parieto-dorsal prefrontal region. These findings suggest that the speech learning resulted in a greater demand of the visual and visuospatial processings subserved by the early visual cortex and parietal cortices. However, only those deaf children who successfully learned the auditory language after CI used more visual motion perception for mouth movement in the left hMT/V5 region and less somatosensory function in the right parieto-frontal region.

Linguistic processing in visual and modality-nonspecific brain areas: PET recordings during selective attention

Positron emission tomography (PET) was used to investigate the neural basis of selective processing of linguistic material during concurrent presentation of multiple stimulus streams ("cocktail-party effect"). Fifteen healthy right-handed adult males were to attend to one of three simultaneously presented messages: one presented visually, one to the left ear, and one to the right ear. During the control condition, subjects attended to visually presented consonant letter strings and ignored auditory messages. This paper reports the modality-nonspecific language processing and visual word-form processing, whereas the auditory attention effects have been reported elsewhere [Cogn. Brain Res. 17 (2003) 201]. The left-hemisphere areas activated by both the selective processing of text and speech were as follows: the inferior prefrontal (Brodmann's area, BA 45, 47), anterior temporal (BA 38), posterior insular (BA 13), inferior (BA 20) and middle temporal (BA 21), occipital (BA 18/30) cortices, the caudate nucleus, and the amygdala. In addition, bilateral activations were observed in the medial occipito-temporal cortex and the cerebellum. Decreases of activation during both text and speech processing were found in the parietal (BA 7, 40), frontal (BA 6, 8, 44) and occipito-temporal (BA 37) regions of the right hemisphere. Furthermore, the present data suggest that the left occipito-temporal cortex (BA 18, 20, 37, 21) can be subdivided into three functionally distinct regions in the posterior-anterior direction on the basis of their activation during attentive processing of sublexical orthography, visual word form, and supramodal higher-level aspects of language.

Specialization within the ventral stream: the case for the visual word form area

Is there specialization for visual word recognition within the visual ventral stream of literate human adults? We review the evidence for a specialized "visual word form area" and critically examine some of the arguments recently placed against this hypothesis. Three distinct forms of specialization must be distinguished: functional specialization, reproducible localization, and regional selectivity. Examination of the literature with this theoretical division in mind indicates that reading activates a precise subpart of the left ventral occipitotemporal sulcus, and that patients with pure alexia consistently exhibit lesions of this region (reproducible localization). Second, this region implements processes adequate for reading in a specific script, such as invariance across upper- and lower-case letters, and its lesion results in the selective loss of reading-specific processes (functional specialization). Third, the issue of regional selectivity, namely, the existence of putative cortical patches dedicated to letter and word recognition, cannot be resolved by positron emission tomography or lesion data, but requires high-resolution neuroimaging techniques. The available evidence from single-subject fMRI and intracranial recordings suggests that some cortical sites respond preferentially to letter strings than to other categories of visual stimuli such as faces or objects, though the preference is often relative rather than absolute. We conclude that learning to read results in the progressive development of an inferotemporal region increasingly responsive to visual words, which is aptly named the visual word form area (VWFA).

Blindness and brain plasticity: contribution of mental imagery?

The purpose of this study was to study brain plasticity in the visual cortex, in six subjects totally blind from birth. The protocol we used was the same as that employed in a prior study on blindfolded sighted subjects (Brain Res., 924 (2002) 176). The production of mental images from animal names versus passive listening to abstract words, involved, in the early blind subjects as well as in the blindfolded sighted subjects of our control group, the superior occipital, inferior and superior parietal areas, premotor area, visual association. Activation foci in the somatosensory areas in the left hemisphere, as well as in the temporal and fusiform gyri were only visible in the blind subjects. The experiment, which was repeated after a short period of rest, demonstrated, this time again, predominant involvement of the dorsal pathway and activation of the primary visual area (in a region of interest). With respect to the ongoing debate on brain reorganization, our study shows that the primary visual area is activated in early blind subjects, and that activation persists in a mental imagery task involving no sensory input other than verbal instructions.

Passive perception of odors and semantic circuits

The sense of smell has been traditionally assumed to be different from other sensory modalities in that odors are encoded perceptually, without a semantic component. Recent findings of improved odor memory upon encoding with verbal cues question this view. Furthermore, familiar odors are easier to remember and discriminate than are unfamiliar ones, and odor familiarity is reported to predict odor naming. To investigate whether familiar odors are processed by different cerebral structures than those that process unfamiliar odors, (15)O H(2)O-positron emission tomography (PET) measurements of cerebral blood flow were carried out in 14 healthy men. The task was passive, birhinal, smelling of familiar odors (FAM), unfamiliar odors (uFAM), and odorless air (AIR). Significant activations (P < 0.05) were calculated using the contrasts FAM-AIR, uFAM-AIR, and FAM-uFAM, and deactivations running these contrasts in the opposite direction. In relation to AIR, both FAM and uFAM activated amygdala, piriform cortex, and parts of anterior cingulate cortex. FAM activated, in addition, left frontal cortex (Brodmann's areas 44,45,47), left parietal cortex incorporating precuneus, and right parahippocampus. Clusters covering parahippocampus and precuneus were observed also in FAM-uFAM. The activation of left frontal cortex and right parahippocampus was positively correlated with familiarity ratings. Smelling of familiar but not unfamiliar odorants seems to engage cerebral circuits mediating memory and language functions, in addition to the engagement of olfactory cortex. Already the most elemental form of odor processing, passive perception thus seems to engage semantic circuits. This is achieved by the ability of odorants to immediately elicit associations and judgments of odor characteristics.

Letter Binding and Invariant Recognition of Masked Words. Behavioral and Neuroimaging Evidence

Fluent readers recognize visual words across changes in case and retinal location, while maintaining a high sensitivity to the arrangement of letters. To evaluate the automaticity and functional anatomy of invariant word recognition, we measured brain activity during subliminal masked priming. By preceding target words with an unrelated prime, a repeated prime, or an anagram made of the same letters, we separated letter-level and whole-word codes. By changing the case and the retinal location of primes and targets, we evaluated the invariance of those codes. Our results indicate that an invariant binding of letters into words is achieved unconsciously through a series of increasingly invariant stages in the left occipito-temporal pathway.

Integration of auditory and visual information about objects in superior temporal sulcus

Two categories of objects in the environment-animals and man-made manipulable objects (tools)-are easily recognized by either their auditory or visual features. Although these features differ across modalities, the brain integrates them into a coherent percept. In three separate fMRI experiments, posterior superior temporal sulcus and middle temporal gyrus (pSTS/MTG) fulfilled objective criteria for an integration site. pSTS/MTG showed signal increases in response to either auditory or visual stimuli and responded more to auditory or visual objects than to meaningless (but complex) control stimuli. pSTS/MTG showed an enhanced response when auditory and visual object features were presented together, relative to presentation in a single modality. Finally, pSTS/MTG responded more to object identification than to other components of the behavioral task. We suggest that pSTS/MTG is specialized for integrating different types of information both within modalities (e.g., visual form, visual motion) and across modalities (auditory and visual).

Beyond sensory images: Object-based representation in the human ventral pathway

We investigated whether the topographically organized, category-related patterns of neural response in the ventral visual pathway are a representation of sensory images or a more abstract representation of object form that is not dependent on sensory modality. We used functional MRI to measure patterns of response evoked during visual and tactile recognition of faces and manmade objects in sighted subjects and during tactile recognition in blind subjects. Results showed that visual and tactile recognition evoked category-related patterns of response in a ventral extrastriate visual area in the inferior temporal gyrus that were correlated across modality for manmade objects. Blind subjects also demonstrated category-related patterns of response in this "visual" area, and in more ventral cortical regions in the fusiform gyrus, indicating that these patterns are not due to visual imagery and, furthermore, that visual experience is not necessary for category-related representations to develop in these cortices. These results demonstrate that the representation of objects in the ventral visual pathway is not simply a representation of visual images but, rather, is a representation of more abstract features of object form.

The recognition potential during sentence presentation: stimulus probability, background stimuli, and SOA

Recognition potential (RP) is an electrical brain response that has proved its usefulness for studying semantic processing of isolated words, and appears when subjects view meaningful stimuli embedded in a stream of background images at a high rate of presentation: the rapid stream stimulation paradigm (RSS). The present technical study is aimed at testing the validity of this procedure in the study of words within sentences. For this purpose, we varied word and background probability of appearance, the number of background stimuli preceding each word, and stimulus onset asynchrony. Probability did not have significant effects on RP, but it was found that a minimum number of two background stimuli preceding each word and a high rate (250 ms) of presentation are preferable for enhancing RP amplitude. The RSS paradigm would therefore improve the visibility-and, hence, refine the analysis-of a component that can nevertheless be obtained with more standard paradigms, such as rapid serial visual presentation, devoid of interspersed background stimuli.

Attention to single letters activates left extrastriate cortex

Brain imaging studies examining the component processes of reading using words, non-words, and letter strings frequently report task-related activity in the left extrastriate cortex. Processing of these linguistic materials involves varying degrees of semantic, phonological, and orthographic analysis that are sensitive to individual differences in reading skill and history. In contrast, single letter processing becomes automatized early in life and is not modulated by later linguistic experience to the same degree as are words. In this study, skilled readers attended to different aspects (single letters, symbols, and colors) of an identical stimulus set during separate sessions of functional magnetic resonance imaging (fMRI). Whereas activation in some portions of ventral extrastriate cortex was shared by attention to both alphabetic and non-alphabetic features, a letter-specific area was identified in a portion of left extrastriate cortex (Brodmann's Area 37), lateral to the visual word form area. Our results demonstrate that while minimizing activity related to word-level lexical properties, cortical responses to letter recognition can be isolated from figural and color characteristics of simple stimuli. The practical utility of this finding is discussed in terms of early identification of reading disability.

Brain activity during intra- and cross-modal priming: new empirical data and review of the literature

A positron emission tomography (PET) study was conducted to investigate the neurofunctional correlate of auditory within-modality and auditory-to-visual cross-modality stem completion priming. Compared to the auditory-to-auditory priming condition, cross-modality priming was associated with a significantly larger regional cerebral blood flow (rCBF) decrease at the boundary between left inferior temporal and fusiform gyri, brain regions previously associated with modality independent lexical retrieval and reading. Instead, within-modality auditory priming was associated with a bilateral pattern of prefrontal rCBF increase. This was likely the expression of more efficient access to output lexical representations and involuntary retrieval of the recent episode during which the just generated word had been encountered.

Evaluation of the dual route theory of reading: a metanalysis of 35 neuroimaging studies

Numerous studies concerned with cerebral structures underlying word reading have been published during the last decade. A few controversies, however, together with methodological or theoretical discrepancies between laboratories, still contribute to blurring the overall view of advances effected in neuroimaging. Carried out within the dual route of reading framework, the aim of this metanalysis was to provide an objective picture of these advances. To achieve this, we used an automated analysis method based on the inventory of activation peaks issued from word or pseudoword reading contrasts of 35 published neuroimaging studies. A first result of this metanalysis was that no cluster of activations has been found more recruited by word than pseudoword reading, implying that the first steps of word access may be common to word and word-like stimuli and would take place within a left occipitotemporal region (previously referred to as the Visual Word Form Area-VWFA) situated in the ventral route, at the junction between inferior temporal and fusiform gyri. The results also indicated the existence of brain regions predominantly involved in one of the two routes to access word. The graphophonological conversion seems indeed to rely on left lateralized brain structures such as superior temporal areas, supramarginal gyrus, and the opercular part of the inferior frontal gyrus, these last two regions reflecting a greater load in working memory during such an access. The lexicosemantic route is thought to arise from the coactivation of the VWFA and semantic areas. These semantic areas would encompass a basal inferior temporal area, the posterior part of the middle temporal gyrus, and the triangular part of inferior frontal gyrus. These results confirm the suitability of the dual route framework to account for activations observed in nonpathological subjects while they read.

Dissociating cortical regions activated by semantic and phonological tasks: a FMRI study in blind and sighted people

Previous neuroimaging studies of language processing in blind individuals described cortical activation of primary (V1) and higher tier visual areas, irrespective of the age of blindness onset. Specifically, participants were given nouns and asked to generate an associated verb. These results confirmed the presence of adaptations in the visual cortex of blind people and suggested that these responses represented linguistic operations. The present functional magnetic resonance imaging study attempted to further characterize these responses as being preferential for semantic or phonological processing. Three groups of participants (sighted, early onset, and late-onset blind) heard lists of related words and attended to either a common meaning (semantic task) or common rhyme (phonological task) that linked the words. In all three groups, the semantic task elicited stronger activity in the left anterior inferior frontal gyrus and the phonological task evoked stronger activity bilaterally in the inferior parietal cortex and posterior aspects of the left inferior frontal gyrus. Only blind individuals showed activity in occipital, temporal, and parietal components of visual cortex. The spatial extent of visual cortex activity was greatest in early blind, who exhibited activation in all ventral and dorsal visual cortex subdivisions (V1 through MT) for both tasks. Preferential activation appeared for the semantic task. Late blind individuals exhibited responses in ventral and dorsal V1, ventral V2, VP and V8, but only for the semantic task. Our findings support prior evidence of visual cortex activity in blind people engaged in auditory language processing and suggest that this activity may be related to semantic processing.

The visual word form area: expertise for reading in the fusiform gyrus

Brain imaging studies reliably localize a region of visual cortex that is especially responsive to visual words. This brain specialization is essential to rapid reading ability because it enhances perception of words by becoming specifically tuned to recurring properties of a writing system. The origin of this specialization poses a challenge for evolutionary accounts involving innate mechanisms for functional brain organization. We propose an alternative account, based on studies of other forms of visual expertise (i.e. bird and car experts) that lead to functional reorganization. We argue that the interplay between the unique demands of word reading and the structural constraints of the visual system lead to the emergence of the Visual Word Form Area.

Early 'visual' cortex activation correlates with superior verbal memory performance in the blind

The visual cortex may be more modifiable than previously considered. Using functional magnetic resonance imaging (fMRI) in ten congenitally blind human participants, we found robust occipital activation during a verbal-memory task (in the absence of any sensory input), as well as during verb generation and Braille reading. We also found evidence for reorganization and specialization of the occipital cortex, along the anterior-posterior axis. Whereas anterior regions showed preference for Braille, posterior regions (including V1) showed preference for verbal-memory and verb generation (which both require memory of verbal material). No such occipital activation was found in sighted subjects. This difference between the groups was mirrored by superior performance of the blind in various verbal-memory tasks. Moreover, the magnitude of V1 activation during the verbal-memory condition was highly correlated with the blind individual's abilities in a variety of verbal-memory tests, suggesting that the additional occipital activation may have a functional role.

The myth of the visual word form area

Recent functional imaging studies have referred to a posterior region of the left midfusiform gyrus as the "visual word form area" (VWFA). We review the evidence for this claim and argue that neither the neuropsychological nor neuroimaging data are consistent with a cortical region specialized for visual word form representations. Specifically, there are no reported cases of pure alexia who have deficits limited to visual word form processing and damage limited to the left midfusiform. In addition, we present functional imaging data to demonstrate that the so-called VWFA is activated by normal subjects during tasks that do not engage visual word form processing such as naming colors, naming pictures, reading Braille, repeating auditory words, and making manual action responses to pictures of meaningless objects. If the midfusiform region has a single function that underlies all these tasks, then it does not correspond to visual word form processing. On the other hand, if the region participates in several functions as defined by its interactions with other cortical areas, then identifying the neural system sustaining visual word form representations requires identification of the set of regions involved. We conclude that there is no evidence that visual word form representations are subtended by a single patch of neuronal cortex and it is misleading to label the left midfusiform region as the visual word form area.

Temporal lobe regions engaged during normal speech comprehension

Processing of speech is obligatory. Thus, during normal speech comprehension, the listener is aware of the overall meaning of the speaker's utterance without the need to direct attention to individual linguistic and paralinguistic (intonational, prosodic, etc.) features contained within the speech signal. However, most functional neuroimaging studies of speech perception have used metalinguistic tasks that required the subjects to attend to specific features of the stimuli. Such tasks have demanded a forced-choice decision and a motor response from the subjects, which will engage frontal systems and may include unpredictable top-down modulation of the signals observed in one or more of the temporal lobe neural systems engaged during speech perception. This study contrasted the implicit comprehension of simple narrative speech with listening to reversed versions of the narratives: the latter are as acoustically complex as speech but are unintelligible in terms of both linguistic and paralinguistic information. The result demonstrated that normal comprehension, free of task demands that do not form part of everyday discourse, engages regions distributed between the two temporal lobes, more widely on the left. In particular, comprehension is dependent on anterolateral and ventral left temporal regions, as suggested by observations on patients with semantic dementia, as well as posterior regions described in studies on aphasic stroke patients. The only frontal contribution was confined to the ventrolateral left prefrontal cortex, compatible with observations that comprehension of simple speech is preserved in patients with left posterior frontal infarction.

Neuroimaging studies of word and pseudoword reading: consistencies, inconsistencies, and limitations

Several functional neuroimaging studies have compared words and pseudowords to test different cognitive models of reading. There are difficulties with this approach, however, because cognitive models do not make clear-cut predictions at the neural level. Therefore, results can only be interpreted on the basis of prior knowledge of cognitive anatomy. Furthermore, studies comparing words and pseudowords have produced inconsistent results. The inconsistencies could reflect false-positive results due to the low statistical thresholds applied or confounds from nonlexical aspects of the stimuli. Alternatively, they may reflect true effects that are inconsistent across subjects; dependent on experimental parameters such as stimulus rate or duration; or not replicated across studies because of insufficient statistical power. In this fMRI study, we investigate consistent and inconsistent differences between word and pseudoword reading in 20 subjects, and distinguish between effects associated with increases and decreases in activity relative to fixation. In addition, the interaction of word type with stimulus duration is explored. We find that words and pseudowords activate the same set of regions relative to fixation, and within this system, there is greater activation for pseudowords than words in the left frontal operculum, left posterior inferior temporal gyrus, and the right cerebellum. The only effects of words relative to pseudowords consistent over subjects are due to decreases in activity for pseudowords relative to fixation; and there are no significant interactions between word type and stimulus duration. Finally, we observe inconsistent but highly significant effects of word type at the individual subject level. These results (i) illustrate that pseudowords place increased demands on areas that have previously been linked to lexical retrieval, and (ii) highlight the importance of including one or more baselines to qualify word type effects. Furthermore, (iii) they suggest that inconsistencies observed in the previous literature may result from effects arising from a small number of subjects only.

An fMRI study comparing brain activation between word generation and electrical stimulation of language-implicated acupoints

We compared the brain activation on functional magnetic resonance imaging (MRI) during word generation with the activation during electrical stimulation of two language-implicated acupoints in 17 healthy, Mandarin-speaking, Chinese male volunteers (age 19-26 years). All subjects were strongly right handed according to a handedness inventory. Using a standard functional MRI procedure and a word-generation paradigm, significant activation was seen in the left and right inferior frontal gyri (BA 44, 45) as well as the left superior temporal gyrus (BA 22, 42). Stronger activation with a larger volume was seen in the left hemisphere. Electrical stimulation of either one of the two language-implicated acupoints, SJ 8 (11 subjects) and Du 15 (6 subjects), without the word-generation paradigm in the same cohort, produced significant activation in the right inferior frontal gyrus (BA 44, 46) and in the left and right superior temporal gyri (BA 22, 42), respectively. Nevertheless, no activation was seen in the left inferior frontal gyrus. In addition, electrical stimulation of the adjacent non-acupoints did not produce any significant brain activation. Although our results support the notion of acupoint-brain activation, applying acupuncture at SJ 8 or Du 15 does not activate the typical language areas in the left inferior frontal cortex.

The neuroanatomical and functional organization of speech perception

A striking property of speech perception is its resilience in the face of acoustic variability (among speech sounds produced by different speakers at different times, for example). The robustness of speech perception might, in part, result from multiple, complementary representations of the input, which operate in both acoustic-phonetic feature-based and articulatory-gestural domains. Recent studies of the anatomical and functional organization of the non-human primate auditory cortical system point to multiple, parallel, hierarchically organized processing pathways that involve the temporal, parietal and frontal cortices. Functional neuroimaging evidence indicates that a similar organization might underlie speech perception in humans. These parallel, hierarchical processing 'streams', both within and across hemispheres, might operate on distinguishable, complementary types of representations and subserve complementary types of processing. Two long-opposing views of speech perception have posited a basis either in acoustic feature processing or in gestural motor processing; the view put forward here might help reconcile these positions.

Functional imaging of the semantic system: retrieval of sensory-experienced and verbally learned knowledge

This paper considers how functional neuro-imaging can be used to investigate the organization of the semantic system and the limitations associated with this technique. The majority of the functional imaging studies of the semantic system have looked for divisions by varying stimulus category. These studies have led to divergent results and no clear anatomical hypotheses have emerged to account for the dissociations seen in behavioral studies. Only a few functional imaging studies have used task as a variable to differentiate the neural correlates of semantic features more directly. We extend these findings by presenting a new study that contrasts tasks that differentially weight sensory (color and taste) and verbally learned (origin) semantic features. Irrespective of the type of semantic feature retrieved, a common semantic system was activated as demonstrated in many previous studies. In addition, the retrieval of verbally learned, but not sensory-experienced, features enhanced activation in medial and lateral posterior parietal areas. We attribute these "verbally learned" effects to differences in retrieval strategy and conclude that evidence for segregation of semantic features at an anatomical level remains weak. We believe that functional imaging has the potential to increase our understanding of the neuronal infrastructure that sustains semantic processing but progress may require multiple experiments until a consistent explanatory framework emerges.

Adaptive changes in early and late blind: a FMRI study of verb generation to heard nouns

Literacy for blind people requires learning Braille. Along with others, we have shown that reading Braille activates visual cortex. This includes striate cortex (V1), i.e., banks of calcarine sulcus, and several higher visual areas in lingual, fusiform, cuneus, lateral occipital, inferior temporal, and middle temporal gyri. The spatial extent and magnitude of magnetic resonance (MR) signals in visual cortex is greatest for those who became blind early in life. Individuals who lost sight as adults, and subsequently learned Braille, still exhibited activity in some of the same visual cortex regions, especially V1. These findings suggest these visual cortex regions become adapted to processing tactile information and that this cross-modal neural change might support Braille literacy. Here we tested the alternative hypothesis that these regions directly respond to linguistic aspects of a task. Accordingly, language task performance by blind persons should activate the same visual cortex regions regardless of input modality. Specifically, visual cortex activity in blind people ought to arise during a language task involving heard words. Eight early blind, six late blind, and eight sighted subjects were studied using functional magnetic resonance imaging (fMRI) during covert generation of verbs to heard nouns. The control task was passive listening to indecipherable sounds (reverse words) matched to the nouns in sound intensity, duration, and spectral content. Functional responses were analyzed at the level of individual subjects using methods based on the general linear model and at the group level, using voxel based ANOVA and t-test analyses. Blind and sighted subjects showed comparable activation of language areas in left inferior frontal, dorsolateral prefrontal, and left posterior superior temporal gyri. The main distinction was bilateral, left dominant activation of the same visual cortex regions previously noted with Braille reading in all blind subjects. The spatial extent and magnitude of responses was greatest on the left in early blind individuals. Responses in the late blind group mostly were confined to V1 and nearby portions of the lingual and fusiform gyri. These results confirm the presence of adaptations in visual cortex of blind people but argue against the notion that this activity during Braille reading represents somatosensory (haptic) processing. Rather, we suggest that these responses can be most parsimoniously explained in terms of linguistic operations. It remains possible that these responses represent adaptations which initially are for processing either sound or touch, but which are later generalized to the other modality during acquisition of Braille reading skills.