The functional anatomy of word comprehension and production

Sensitivity to Voice in Human Prefrontal Cortex

We report two functional MRI (fMRI) experiments showing sensitivity to human voice in a region of human left inferior prefrontal cortex, pars orbitalis. The voice-enhanced response was observed for speech as well as nonlinguistic vocalizations and was stronger for emotional than neutral vocalizations. This region could constitute a human prefrontal auditory domain similar to the one recently identified in the macaque brain.

Differential activity in left inferior frontal gyrus for pseudowords and real words: an event-related fMRI study on auditory lexical decision

After Newman and Twieg and others, we used a fast event-related functional magnetic resonance imaging (fMRI) design and contrasted the lexical processing of pseudowords and real words. Participants carried out an auditory lexical decision task on a list of randomly intermixed real and pseudo Chinese two-character (or two-syllable) words. The pseudowords were constructed by recombining constituent characters of the real words to control for sublexical code properties. Processing of pseudowords and real words activated a highly comparable network of brain regions, including bilateral inferior frontal gyrus, superior, middle temporal gyrus, calcarine and lingual gyrus, and left supramarginal gyrus. Mirroring a behavioral lexical effect, left inferior frontal gyrus (IFG) was significantly more activated for pseudowords than for real words. This result disconfirms a popular view that this area plays a role in grapheme-to-phoneme conversion, as such a conversion process was unnecessary in our task with auditory stimulus presentation. An alternative view was supported that attributes increased activity in left IFG for pseudowords to general processes in decision making, specifically in making positive versus negative responses. Activation in left supramarginal gyrus was of a much larger volume for real words than for pseudowords, suggesting a role of this region in the representation of phonological or semantic information for two-character Chinese words at the lexical level.

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.

Functional anatomy of biological motion perception in posterior temporal cortex: an FMRI study of eye, mouth and hand movements

Passive viewing of biological motion engages extensive regions of the posterior temporal-occipital cortex in humans, particularly within and nearby the superior temporal sulcus (STS). Relatively little is known about the functional specificity of this area. Some recent studies have emphasized the perceived intentionality of the motion as a potential organizing principle, while others have suggested the existence of a somatotopy based upon the limb perceived in motion. Here we conducted an event-related functional magnetic resonance imaging experiment to compare activity elicited by movement of the eyes, mouth or hand. Each motion evoked robust activation in the right posterior temporal-occipital cortex. While there was substantial overlap of the activation maps in this region, the spatial distribution of hemodynamic response amplitudes differentiated the movements. Mouth movements elicited activity along the mid-posterior STS while eye movements elicited activity in more superior and posterior portions of the right posterior STS region. Hand movements activated more inferior and posterior portions of the STS region within the posterior continuing branch of the STS. Hand-evoked activity also extended into the inferior temporal, middle occipital and lingual gyri. This topography may, in part, reflect the role of particular body motions in different functional activities.

Functional neuroanatomy of human vocalization: an H215O PET study

Vocalization in lower animals is associated with a well-described visceromotor call system centered on the mesencephalic periacqueductal grey matter (PAG), which is itself regulated by paramedian cortical structures. To determine the role this phylogenetically older system plays in human phonation, we contrasted voiced and unvoiced speech using positron emission tomography and then evaluated functional connectivity of regions that significantly differentiated these conditions. Vocalization was associated with increased and highly correlated activity within the midline structures--PAG and paramedian cortices--described in lower mammalian species. Concurrent activation and connectivity of neocortical and subcortical motor regions--medial and lateral premotor structures and elements of basal ganglia thalamocortical circuitry--suggest a mechanism by which this system may have come under an increasing degree of voluntary control in humans. Additionally, areas in the temporal lobe and cerebellum were selectively activated during voiced but not unvoiced speech. These regions are functionally coupled to both visceromotor and neocortical motor areas during production of voiced speech, suggesting they may play a central role in self-monitoring and feedback regulation of human phonation.

Functional connectivity during Stroop task performance

Using covariance-based multivariate analysis, we examined patterns of functional connectivity in rCBF on a practice-extended version of the Stroop color-word paradigm. Color-word congruent and incongruent conditions were presented in six AB trials to healthy subjects during 12 H2(15)O PET scans. Analyses identified two reproducible canonical eigenimages (CE) from the PET data, which were converted to a standard Z score scale after cross-validation resampling and correction for random subject effects. The first CE corresponded to practice-dependent changes in covarying rCBF that occurred over early task repetitions and correlated with improved behavioral performance. This included many regions previously implicated by PET and fMRI studies of this task, which we suggest may represent two "parallel" networks: (i) a cingulo-frontal system that was initially engaged in selecting and mapping a task-relevant response (color naming) when the attentional demands of the task were greatest; and (ii) a ventral visual processing stream whose concurrent decrease in activity represented the task-irrelevant inhibition of word reading. The second CE corresponded to a consistent paradigmatic effect of Stroop interference on covarying rCBF. Coactivations were located in dorsal and ventral prefrontal regions as well as frontopolar cortex. This pattern supports existing evidence that prefrontal regions are involved in maintaining attentional control over conflicting response systems. Taken together, these findings may be more in line with theoretical models that emphasize a role for practice in the emergence of Stroop phenomena. These findings may also provide some additional insight into the nature of anterior cingulate- and prefrontal cortical contributions to implementing cognitive control in the brain.

Neural Representation of Vocalizations in the Primate Ventrolateral Prefrontal Cortex

In this study, we examined the role of the ventrolateral prefrontal cortex in encoding communication stimuli. Specifically, we recorded single-unit responses from the ventrolateral prefrontal cortext (vlPFC) in awake behaving rhesus macaques in response to species-specific vocalizations. We determined the selectivity of vlPFC cells for 10 types of rhesus vocalizations and also asked what types of vocalizations cluster together in the neuronal response. The data from the present study demonstrate that vlPFC auditory neurons respond to a variety of species-specific vocalizations from a previously characterized library. Most vlPFC neurons responded to two to five vocalizations, while a small percentage of cells responded either selectively to a particular vocalization type or nonselectively to most auditory stimuli tested. Use of information theoretic approaches to examine vocalization tuning indicates that on average, vlPFC neurons encode information about one or two vocalizations. Further analysis of the types of vocalizations that vlPFC cells typically respond to using hierarchical cluster analysis suggests that the responses of vlPFC cells to multiple vocalizations is not based strictly on the call's function or meaning but may be due to other features including acoustic morphology. These data are consistent with a role for the primate vlPFC in assessing distinctive acoustic features.

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.

Seeing and hearing others and oneself talk

We studied the modification of auditory perception in three different conditions in twenty subjects. Observing other person's discordant articulatory gestures deteriorated identification of acoustic speech stimuli and modified the auditory percept, causing a strong McGurk effect. A similar effect was found when the subjects watched their own silent articulation in a mirror and acoustic stimuli were simultaneously presented to their ears. Interestingly, a smaller but significant effect was even obtained when the subjects just silently articulated the syllables without visual feedback. On the other hand, observing other person's or one's own concordant articulation and silently articulating a concordant syllable improved identification of the acoustic stimuli. The modification of auditory percepts caused by visual observation of speech and silently articulating it are both suggested to be due to the alteration of activity in the auditory cortex. Our findings support the idea of a close relationship between speech perception and production.

Hemispheric asymmetries of hypometabolism associated with semantic memory impairment in Alzheimer's disease: a study using positron emission tomography with fluorodeoxyglucose-F18

Considerable disagreement exists about the neuroanatomical basis of conceptual-semantic impairments observed in a subgroup of patients with Alzheimer's disease (AD) at mild to moderate stages of the disease. Several studies of groups of patients have shown correlations between focal hypometabolism or hypoperfusion in left hemispheric areas and measures of verbal semantic memory impairment in AD patients. The question remains, however, whether left hemispheric hypometabolism is sufficient to produce such impairment in the single case and whether nonverbal semantic knowledge is also affected. We used positron emission tomography (PET) with fluorodeoxyglucose-F18 (FDG), statistical parametric mapping (SPM), and tests of verbal and nonverbal semantic memory in 11 AD patients with a mean score on the Mini-Mental State Examination of 22.6 (+/-2.8). Naming impairment was significantly associated with left hemispheric asymmetry of hypometabolism on a single-case basis. Our correlation analysis showed that metabolism in left anterior temporal, posterior inferior temporal, inferior parietal and medial occipital areas (Brodmann areas: 21/38, 37, 40 and 19) correlated with both verbal and nonverbal semantic performance. We conclude that left hemispheric synaptic dysfunction, as measured by regional glucose hypometabolism, was sufficient to produce semantic impairments in our patients. The majority of areas affected in our patients with semantic impairments were involved in multimodal or supramodal (verbal and nonverbal) semantic knowledge.

Paradigm design of sensory-motor and language tests in clinical fMRI

Functional magnetic resonance imaging (fMRI) paradigms on sensory-motor and language functions are reviewed from a clinical user's perspective. The objective was to identify special requirements regarding the design of fMRI paradigms for clinical applications. A wide range of methods for setting up fMRI examinations were found in the literature. It was concluded that there is a need for standardised procedures adapted for clinical settings. Sensory-motor activation patterns do not vary much at different hand motion tasks. Nevertheless it is one of the most important clinical tests. In contrast, the language system is much more complex. In several studies it has been observed that word production tasks are preferable in determination of language lateralisation. Broca's area is activated by most tasks, whereas sentence processing and semantic decision also involve activation in temporoparietal and frontal areas. However, combined task analysis (CTA) of several different tasks has been found to be more robust and reliable for clinical fMRI compared to separate task analysis.

Implicit and explicit processing of kanji and kana words and non-words studied with fMRI

Using functional magnetic resonance imaging (fMRI), we investigated the implicit language processing of kanji and kana words (i.e., hiragana transcriptions of normally written kanji words) and non-words. Twelve right-handed native Japanese speakers performed size judgments for character stimuli (implicit language task for linguistic stimuli), size judgments for scrambled-character stimuli (implicit language task for non-linguistic stimuli), and lexical decisions (explicit language task). The size judgments for scrambled-kanji stimuli and scrambled-kana stimuli produced activations on the bilateral lingual gyri (BA 18), the bilateral occipitotemporal regions (BA 19/37), and the bilateral superior and inferior parietal cortices (BA 7/40). Interestingly, besides these areas, activations of the left inferior frontal region (Broca's area, BA 44/45) and the left posterior inferior temporal cortex (PITC, BA 37), which have been considered as language areas, were additionally activated during size judgment for kanji character stimuli. Size judgment for kana character stimuli also activated Broca's area, the left PITC, and the left supramarginal gyrus (SMG, BA 40). The activations of these language areas were replicated in the lexical decisions for both kanji and kana. These findings suggest that language processing of both kanji and kana scripts is obligatory to literate Japanese subjects. Moreover, comparison between the scrambled kanji and the scrambled kana showed no activation in the language areas, while greater activation in the bilateral fusiform gyri (left-side predominant) was found in kanji vs. kana comparison during the size judgment and the lexical decision. Kana minus kanji activated the left SMG during the size judgment, and Broca's area and the left middle/superior temporal junction during the lexical decision. These results probably reflect that in implicit or explicit reading of kanji words and kana words (i.e., hiragana transcriptions of kanji words), although using largely overlapping cortical regions, there are still some differences. Kanji reading may involve more heavily visual orthographic retrieval and lexical-semantic system through the ventral route, while kana transcriptions of kanji words require phonological recoding to gain semantic access through the dorsal route.

An fMRI Investigation of Speech and Tone Segmentation

Recent research strongly indicates that phonological tasks activate a subregion of the inferior frontal gyrus. The purpose of the present fMRI study was to investigate the extent to which activation of this region during phonological processing is due to speech processes per se such as articulatory recoding or to other cognitive task demands such as working memory. Thus, we compared activation patterns during segmentation of speech and tone sequences to a tone discrimination task. In particular, participants performed same/different judgments on pairs of words, pseudowords, and tone sequences that required segmentation of a continuous acoustic signal as well as tone pairs that did not require segmentation. Accuracy and reaction time data showed that speech and tone sequence segmentation conditions patterned more similarly to each other than to tone discrimination pairs. Analyses of group data revealed strong activation of the region at the border of the left inferior and middle frontal gyrus for all three segmentation conditions compared to tone discrimination, but no consistent differences were observed when word and pseudoword segmentation were directly contrasted. Analyses of individual subjects indicated that a large number of participants activated a small area of the middle frontal gyrus during the speech conditions compared to the sequences. These results suggest that a significant portion of active frontal areas is recruited for extracting acoustic information and maintaining it in memory for decision. However, some regions at the border of the inferior/middle frontal gyrus may be unique to speech segmentation.

Dissociation of lexical syntax and semantics: evidence from focal cortical degeneration

The question of whether information relevant to meaning (semantics) and structure (syntax) relies on a common language processor or on separate subsystems has proved difficult to address definitively because of the confounds involved in comparing the two types of information. At the sentence level syntactic and semantic judgments make different cognitive demands, while at the single word level, the most commonly used syntactic distinction (between nouns and verbs) is confounded with a fundamental semantic difference (between objects and actions). The present study employs a different syntactic contrast (between count nouns and mass nouns), which is crossed with a semantic difference (between naturally occurring and man-made substances) applying to words within a circumscribed semantic field (foodstuffs). We show, first, that grammaticality judgments of a patient with semantic dementia are indistinguishable from those of a group of age-matched controls, and are similar regardless of the status of his semantic knowledge about the item. In a second experiment we use the triadic task in a group of age-matched controls to show that similarity judgments are influenced not only by meaning (natural vs. manmade), but also implicitly by syntactic information (count vs. mass). Using the same task in a patient with semantic dementia we show that the semantic influences on the syntactic dimension are unlikely to account for this pattern in normals. These data are discussed in relation to modular vs. nonmodular models of language processing, and in particular to the semantic-syntactic distinction.

Cortical lateralization during verb generation: a combined ERP and fMRI study

Lateralization of scalp-recorded event-related potentials (ERPs) and functional MRI (fMRI) activation was investigated using a verb generation task in 10 healthy right-handed adults. ERPs showed an early transient positivity in the left inferior temporal region (500-1250 ms) following auditory presentation of the stimulus noun. A sustained slow cortical negativity of later onset (1250-3000 ms) was then recorded, most pronounced over left inferior frontal regions. fMRI data were in agreement with both ERP effects, showing left lateralized activation in inferior and superior temporal as well as inferior frontal cortices. Lateralized ERP effects occurred during the verb generation task but not during passive word listening or during word- and nonword repetition. Thus, ERPs and fMRI provided convergent evidence regarding language lateralization, with ERPs revealing the temporal sequence of posterior to anterior cortical activation during semantic retrieval.

The cerebellum and decision making under uncertainty

This study aimed to identify the neural basis of probabilistic reasoning, a type of inductive inference that aids decision making under conditions of uncertainty. Eight normal subjects performed two separate two-alternative-choice tasks (the balls in a bottle and personality survey tasks) while undergoing functional magnetic resonance imaging (fMRI). The experimental conditions within each task were chosen so that they differed only in their requirement to make a decision under conditions of uncertainty (probabilistic reasoning and frequency determination required) or under conditions of certainty (frequency determination required). The same visual stimuli and motor responses were used in the experimental conditions. We provide evidence that the neo-cerebellum, in conjunction with the premotor cortex, inferior parietal lobule and medial occipital cortex, mediates the probabilistic inferences that guide decision making under uncertainty. We hypothesise that the neo-cerebellum constructs internal working models of uncertain events in the external world, and that such probabilistic models subserve the predictive capacity central to induction.

Recovery of semantic word processing in global aphasia: a functional MRI study

One important issue concerning the recovery of higher cognitive functions-such as word comprehension in aphasia-is to what extent impairments can be compensated for by intact parts of the network of areas normally involved in a closely related function ("redundancy recovery"). In a previous functional MRI investigation, we were able to show that left hemispheric redundancy recovery within a distributed system of related lexical-semantic functions was the most probable basis of recovery of comprehension from transcortical sensory aphasia. The question remained, however, whether redundancy recovery may play a more general role in the recovery of comprehension after large left hemispheric lesions and severe aphasia. We had the possibility, using the same fMRI paradigm, to study seven cases with left middle cerebral artery (MCA) infarction and partial recovery of comprehension > or =6 months after presentation with global aphasia on acute assessment. Lateralization of activation did not differ significantly between patients and controls. The most consistent regions of activation included the left extrasylvian posterior temporal and the right posterior parietal cortex. Recovery of language comprehension was associated predominantly with activations in regions, which were also activated in several normal subjects. We suggest that a redundancy recovery mechanism within multiple representations of closely related functions was more important than take-over of function by previously unrelated areas (vicariation) as the basis of recovery of word comprehension in our patients in spite of extensive left hemispheric damage. We conclude that redundancy within the lexical-semantic system seems to make an important contribution to recovery of comprehension even in severe aphasia.

Developmental dyslexia

Developmental dyslexia, or specific reading disability, is a disorder in which children with normal intelligence and sensory abilities show learning deficits for reading. Substantial evidence has established its biological origin and the preponderance of phonological disorders even though important phenotypic variability and comorbidity have been recorded. Diverse theories have been proposed to account for the cognitive and neurological aspects of dyslexia. Findings of genetic studies show that different loci affect specific reading disability although a direct relation has not been established between symptoms and a given genomic locus. In both children and adults with dyslexia, results of neuroimaging studies suggest defective activity and abnormal connectivity between regions crucial for language functions--eg, the left fusiform gyrus for reading--and changes in brain activity associated with performance improvement after various remedial interventions.

Analysis of neural mechanisms underlying verbal fluency in cytoarchitectonically defined stereotaxic space—The roles of Brodmann areas 44 and 45

We investigated neural activations underlying a verbal fluency task and cytoarchitectonic probabilistic maps of Broca's speech region (Brodmann's areas 44 and 45). To do so, we reanalyzed data from a previous functional magnetic resonance imaging (fMRI) [Brain 125 (2002) 1024] and from a cytoarchitectonic study [J. Comp. Neurol. 412 (1999) 319] and developed a method to combine both data sets. In the fMRI experiment, verbal fluency was investigated in 11 healthy volunteers, who covertly produced words from predefined categories. A factorial design was used with factors verbal class (semantic vs. overlearned fluency) and switching between categories (no vs. yes). fMRI data analysis employed SPM99 (Statistical Parametric Mapping). Cytoarchitectonic maps of areas 44 and 45 were derived from histologic sections of 10 postmortem brains. Both the in vivo fMRI and postmortem MR data were warped to a common reference brain using a new elastic warping tool. Cytoarchitectonic probability maps with stereotaxic information about intersubject variability were calculated for both areas and superimposed on the functional data, which showed the involvement of left hemisphere areas with verbal fluency relative to the baseline. Semantic relative to overlearned fluency showed greater involvement of left area 45 than of 44. Thus, although both areas participate in verbal fluency, they do so differentially. Left area 45 is more involved in semantic aspects of language processing, while area 44 is probably involved in high-level aspects of programming speech production per se. The combination of functional data analysis with a new elastic warping tool and cytoarchitectonic maps opens new perspectives for analyzing the cortical networks involved in language.

Neural correlates of lexical and sublexical processes in reading

The purpose of the present study was to compare the brain regions and systems that subserve lexical and sublexical processes in reading. In order to do so, three types of tasks were used: (i). silent reading of very high frequency regular words (lexical task); (ii). silent reading of nonwords (sublexical task); and, (iii). silent reading of very low frequency regular words (sublexical task). All three conditions were contrasted with a visual/phonological baseline condition. The lexical condition engaged primarily an area at the border of the left angular and supramarginal gyri. Activation found in this region suggests that this area may be involved in mapping orthographic-to-phonological whole word representations. Both sublexical conditions elicited significantly greater activation in the left inferior prefrontal gyrus. This region is thought to be associated with sublexical processes in reading such as grapheme-to-phoneme conversion, phoneme assembly and underlying verbal working memory processes. Activation in the left IFG was also associated with left superior and middle temporal activation. These areas are thought to be functionally correlated with the left IFG and to contribute to a phonologically based form of reading. The results as a whole demonstrate that lexical and sublexical processes in reading activate different regions within a complex network of brain structures.

Double dissociation between picture naming and comprehension: an electrostimulation study

We performed a cortico-subcortical language electrical mapping, using a picture naming task and a semantic test of association, during resection of a left posterior temporal glioma in an awake patient. Two discrete naming sites were identified in the posterior part of the left superior temporal gyrus, plus a third distinct site between the two previous areas, inducing specific comprehension disorders without anomia when stimulated. After resection, white matter stimulation elicited anomia without comprehension disorder. We suggest the existence of distinct naming and comprehension systems, which can explain the possibility of a double dissociation aphasic syndrome: one with normal undertanding but naming error, reflecting post-semantic problems of access to the phonological form; the other with correct naming but without normal comprehension, testifying to a direct non-semantic pathway for naming.

Learning complex arithmetic—an fMRI study

Aim of the present functional magnet resonance imaging (fMRI) study was to detect modifications of cerebral activation patterns related to learning arithmetic. Thirteen right-handed subjects were extensively trained on a set of 18 complex multiplication problems. In the following fMRI session, trained and untrained problems (closely matched for difficulty) were presented in blocked order alternating with a number matching task and a fact retrieval task. Importantly, left hemispheric activations were dominant in the two contrasts between untrained and trained condition, suggesting that learning processes in arithmetic are predominantly supported by the left hemisphere. Contrasting untrained versus trained condition, the left intraparietal sulcus showed significant activations, as well as the inferior parietal lobule. A further significant activation was found in the left inferior frontal gyrus. This activation may be accounted for by higher working memory demands in the untrained as compared to the trained condition. Contrasting trained versus untrained condition a significant focus of activation was found in the left angular gyrus. Following the triple-code model [Science 284 (1999) 970], the shift of activation within the parietal lobe from the intraparietal sulcus to the left angular gyrus suggests a modification from quantity-based processing to more automatic retrieval. The present study shows that the left angular gyrus is not only involved in arithmetic tasks requiring simple fact retrieval, but may show significant activations as a result of relatively short training of complex calculation.

An Event-Related fMRI Investigation of Implicit Semantic Priming

The neural basis underlying implicit semantic priming was investigated using event-related fMRI. Prime-target pairs were presented auditorily for lexical decision (LD) on the target stimulus, which was either semantically related or unrelated to the prime, or was a nonword. A tone task was also administered as a control. Behaviorally, all participants demonstrated semantic priming in the LD task. fMRI results showed that for all three conditions of the LD task, activation was seen in the superior temporal gyrus (STG), the middle temporal gyrus (MTG), and the inferior parietal lobe, with greater activation in the unrelated and nonword conditions than in the related condition. Direct comparisons of the related and unrelated conditions revealed foci in the left STG, left precentral gyrus, left and right MTGs, and right caudate, exhibiting significantly lower activation levels in the related condition. The reduced activity in the temporal lobe suggests that the perception of the prime word activates a lexical— semantic network that shares common elements with the target word, and, thus, the target can be recognized with enhanced neural efficiency. The frontal lobe reductions most likely reflect the increased efficiency in monitoring the activation of lexical representations in the temporal lobe, making a decision, and planning the appropriate motor response.

Subthalamic nucleus stimulation affects a frontotemporal network: A PET study

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has become an effective strategy in the treatment of motor symptoms in advanced Parkinson's disease. However, clinical studies have shown that DBS can affect verbal fluency. Seven Parkinson's disease patients with bilateral DBS of the STN were studied with positron emission tomography (PET) to investigate the effects of STN stimulation on regional cerebral blood flow during a verbal fluency task. Activation of the right orbitofrontal cortex and verbal fluency-associated activation within a left-sided frontotemporal network were decreased during STN stimulation compared with the OFF state. Our results offer an explanation for the commonest neuropsychological side effect of STN stimulation and show that STN stimulation affects a frontotemporal network during a fluency task.

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.

Acute conduction aphasia: an analysis of 20 cases

In this study, the linguistic performance of 20 patients with acute conduction aphasia (CA) is described. CA presented as a relatively homogeneous aphasic syndrome characterized by a severe impairment of repetition and fluent expressive language functions with frequent phonemic paraphasias, repetitive self-corrections, word-finding difficulties, and paraphrasing. Language comprehension as assessed by tests of auditory and reading comprehension was only mildly impaired, whereas most patients performed poorly on the Token Test. Verbal-auditory short-term memory was reduced in all patients except one and seems to play a role in associated cognitive deficits, such as impaired syntactic comprehension or reduced mental arithmetics. A follow-up examination of 12 patients showed that CA often resulted in a chronic language deficit. Lesion locations were the posterior temporal and inferior parietal lobe.

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.

Mechanisms underlying perseveration in aphasia: evidence from a single case study

Aphasic individuals often inappropriately and unintentionally repeat recent responses, errors termed recurrent perseverations. In a series of picture naming experiments, we investigated the impact of manipulating stimulus factors on the number of perseverations produced by an aphasic patient (E.B.) with markedly impaired naming skills. E.B. produced significantly more perseverations to pictures with low frequency names and following stimulus repetition. In contrast, semantic relatedness and presentation rate failed to influence perseveration. Our results are considered in the context of theories that relate recurrent perseverations to intact priming mechanisms [Brain 121 (1998) 1641; Aphasiology 12 (1998) 319; J. Exp. Psychol. Learn. Mem. Cogn. 19 (1993) 243]. We conclude that these theories can correctly predict some but not all aspects of E.B.'s perseverations. In particular, they failed to predict that: (1) perseverations often appeared to reflect the earlier sequential proximity of stimuli and responses; and (2) perseverations became less likely as more experimental trials intervened, a trend that did not interact with presentation rate. We review evidence relating recurrent perseverations to neuromodulatory deficits and we conclude that a theory of the functional role of neuromodulation in the cerebral cortex proposed by Hasselmo [Neural Netw. 7 (1994) 13] is capable of accounting for all aspects of E.B.'s perseverative behavior.

Effects of word form on brain processing of written Chinese

Both logographic characters and alphabetic pinyins can be used to write words in Chinese. Here we use fMRI to address the question of whether the written form affects brain processing of a word. Fifteen healthy, right-handed, native Chinese-reading volunteers participated in our study and were asked to read silently either Chinese characters (8 subjects) or pinyins (7 subjects). The stimulus presentation rate was varied for both tasks to allow us to identify brain regions with word-load-dependent activation. Rate effects (fast minus slow presentations) for Chinese character reading were observed in striate and extrastriate visual cortex, superior parietal lobule, left posterior middle temporal gyrus, bilateral inferior temporal gyri, and bilateral superior frontal gyri. Rate effects for pinyin reading were observed in bilateral fusiform, lingual, and middle occipital gyri, bilateral superior parietal lobule/precuneus, left inferior parietal lobule, bilateral inferior temporal gyrus, left middle temporal gyrus, and left superior temporal gyrus. These results demonstrate that common regions of the brain are involved in reading both Chinese characters and pinyins, activated apparently independently of the surface form of the word. There also appear to be brain regions in which activation is dependent on word form. However, it is unlikely that these are entirely specific for a given word form; their activation more likely reflects relative functional specializations within broader networks for processing written language.

Testing for dual brain processing routes in reading: a direct contrast of chinese character and pinyin reading using FMRI

Chinese offers a unique tool for testing the effects of word form on language processing during reading. The processes of letter-mediated grapheme-to-phoneme translation and phonemic assembly (assembled phonology) critical for reading and spelling in any alphabetic orthography are largely absent when reading nonalphabetic Chinese characters. In contrast, script-to-sound translation based on the script as a whole (addressed phonology) is absent when reading the Chinese alphabetic sound symbols known as pinyin, for which the script-to-sound translation is based exclusively on assembled phonology. The present study aims to contrast patterns of brain activity associated with the different cognitive mechanisms needed for reading the two scripts. fMRI was used with a block design involving a phonological and lexical task in which subjects were asked to decide whether visually presented, paired Chinese characters or pinyin "sounded like" a word. Results demonstrate that reading Chinese characters and pinyin activate a common brain network including the inferior frontal, middle, and inferior temporal gyri, the inferior and superior parietal lobules, and the extrastriate areas. However, some regions show relatively greater activation for either pinyin or Chinese reading. Reading pinyin led to a greater activation in the inferior parietal cortex bilaterally, the precuneus, and the anterior middle temporal gyrus. In contrast, activation in the left fusiform gyrus, the bilateral cuneus, the posterior middle temporal, the right inferior frontal gyrus, and the bilateral superior frontal gyrus were greater for nonalphabetic Chinese reading. We conclude that both alphabetic and nonalphabetic scripts activate a common brain network for reading. Overall, there are no differences in terms of hemispheric specialization between alphabetic and nonalphabetic scripts. However, differences in language surface form appear to determine relative activation in other regions. Some of these regions (e.g., the inferior parietal cortex for pinyin and fusiform gyrus for Chinese characters) are candidate regions for specialized processes associated with reading via predominantly assembled (pinyin) or addressed (Chinese character) procedures.

Functional integration and inference in the brain

Self-supervised models of how the brain represents and categorises the causes of its sensory input can be divided into two classes: those that minimise the mutual information (i.e. redundancy) among evoked responses and those that minimise the prediction error. Although these models have similar goals, the way they are attained, and the functional architectures employed, can be fundamentally different. This review describes the two classes of models and their implications for the functional anatomy of sensory cortical hierarchies in the brain. We then consider how empirical evidence can be used to disambiguate between architectures that are sufficient for perceptual learning and synthesis. Most models of representational learning require prior assumptions about the distribution of sensory causes. Using the notion of empirical Bayes, we show that these assumptions are not necessary and that priors can be learned in a hierarchical context. Furthermore, we try to show that learning can be implemented in a biologically plausible way. The main point made in this review is that backward connections, mediating internal or generative models of how sensory inputs are caused, are essential if the process generating inputs cannot be inverted. Because these processes are dynamical in nature, sensory inputs correspond to a non-invertible nonlinear convolution of causes. This enforces an explicit parameterisation of generative models (i.e. backward connections) to enable approximate recognition and suggests that feedforward architectures, on their own, are not sufficient. Moreover, nonlinearities in generative models, that induce a dependence on backward connections, require these connections to be modulatory; so that estimated causes in higher cortical levels can interact to predict responses in lower levels. This is important in relation to functional asymmetries in forward and backward connections that have been demonstrated empirically. To ascertain whether backward influences are expressed functionally requires measurements of functional integration among brain systems. This review summarises approaches to integration in terms of effective connectivity and proceeds to address the question posed by the theoretical considerations above. In short, it will be shown that functional neuroimaging can be used to test for interactions between bottom-up and top-down inputs to an area. The conclusion of these studies points toward the prevalence of top-down influences and the plausibility of generative models of sensory brain function.

The brain circuitry of syntactic comprehension

Syntactic comprehension is a fundamental aspect of human language, and has distinct properties from other aspects of language (e.g. semantics). In this article, we aim to identify if there is a specific locus of syntax in the brain by reviewing imaging studies on syntactic processing. We conclude that results from neuroimaging support evidence from neuropsychology that syntactic processing does not recruit one specific area. Instead a network of areas including Broca's area and anterior, middle and superior areas of the temporal lobes is involved. However, none of these areas appears to be syntax specific.

"Pray or Prey?" dissociation of semantic memory retrieval from episodic memory processes using positron emission tomography and a novel homophone task

One problem in studying the neural basis of semantic memory using functional neuroimaging is that it is often difficult to disentangle activation associated with semantic memory retrieval from that associated with episodic memory encoding and retrieval. To address this issue, a novel homophone task was used in which subjects were PET scanned whilst learning a series of real words (e.g., prey). In a subsequent scan, the subjects were presented with homophone pairs (e.g., prey vs pray) and were required to choose the one that had been shown previously. In two corresponding baseline tasks, the subjects were scanned whilst learning and recognizing pronounceable nonwords. Thus, while all of these tasks recruited either episodic memory encoding or retrieval processes, only the homophone tasks involved semantic memory retrieval. A conjunction analysis designed to isolate activation associated with semantic memory retrieval, revealed changes in several left lateral frontal regions (BA 9/10, 9/45), the left middle temporal cortex (BA 21), and in the left inferior temporoparietal cortex (BA 39). In contrast, a conjunction analysis designed to isolate activation associated with episodic memory encoding, revealed significant changes in the left hippocampus, as well as in the frontopolar cortex (BA 10) bilaterally, the left inferior parietal cortex (BA 40), and the left superior temporal gyrus (BA 22, 28). The present results clarify and extend recent attempts to understand the neural basis of semantic memory retrieval, by actively controlling for the confounding effects of episodic memory encoding and retrieval processes.

Distinct areas in parietal cortex involved in long-term and short-term action planning: a PET investigation

The sequential organization of events within a script, can be considered as a means to explore the cognitive mechanisms involved in action planning. Scripts are composed of goal-oriented sequences of events that typically occur in a specific and systematic order. The purpose of this study was to investigate the effect of temporal variation between script events (short-term versus long-term) on neural activity in normal volunteers. Subjects were required to judge whether the chronological order of three events was correct or not, while regional cerebral blood flow was measured using positron emission tomography. The modality of script presentation (graphic versus lexical) was manipulated. In the left hemisphere, the supramarginal gyrus, the middle frontal gyrus, the inferior temporal gyrus, and the middle occipital gyrus were more activated in the short-term script conditions, while the angular gyrus, the medial superior frontal gyrus, the precuneus bilaterally, the anterior cingulate gyrus and the inferior and middle temporal gyrus on the left were more involved during long-term scripts processing. The occipito-temporal junction (MT/V5) was significantly more activated in the graphic conditions as compared to the lexical ones, and in the short-term scripts conditions as compared to the long-term ones although all stimuli were static. Our results support the notion that two distinct frontal-parietal networks are engaged in short-term and long-term script processing. In addition, our study demonstrates two kinds of dissociations in the parietal lobe. A macro-dissociation between the anterior and the posterior portion of the inferior parietal lobe was found which accounts for processing short-term and long-term scripts respectively, as well as a micro-dissociation in each of these regions which is associated with distinct processing depending on the presentation modalities. These results may help to better understand apraxia at the neurophysiological level.

A space for measuring mind and brain: interdisciplinarity and digital tools in the development of brain mapping and functional imaging, 1980-1990

Brain mapping is said to have opened up the possibility of a new collaboration between the sciences of mind and the sciences of the brain, potentially leading to a new kind of scientist, sometimes called "cognitive neuroscientist." This article traces the recent history of brain mapping and analyzes the processes that have led to a new "close working relationship" between the sciences of mind and brain. A key part of the working relationship is shown to be constituted through the development of the Talairach system, a digital space in which to measure structure and function. The development of meaningful brain mapping data involves the creation of measurement spaces that allow interdisciplinary collaboration and is not the result solely of theoretical developments or of the application of a technology.

Posterior parietal cortex is implicated in continuous switching between verbal fluency tasks: an fMRI study with clinical implications

We investigated whether posterior parietal cortex controls attentional switching when the tasks involve neither spatial nor visual cognition. Normal volunteers were scanned using functional MRI (fMRI). In all conditions, subjects were required to covertly produce words in verbal fluency tasks. They did so at a rate of one every 2 s (with eyes closed) in response to an auditory beep. In the non-switching (NS) trials, subjects responded with a series of items from a prespecified semantic category (SC) (e.g. fruits or cars) and from overlearned sequences (OSs) (days of the week, months of the year or letters of the alphabet). Instructions as to which category items should be drawn from on a given run of trials were presented over fMRI-compatible earphones prior to each run. In the switching (S) trials, subjects produced a series of word triads from three SCs: for example, fruits, cars and furniture (e.g. pear, Mercedes, table.); and from three OSs: days of the week, months of the year and letters of the alphabet (e.g. Monday, January, A.). This design is factorial, with the factors verbal class (SC or OSs) and switching conditions (S or NS). Increases in neural activity (P < 0.05, corrected for multiple comparisons) were observed only in superior posterior parietal cortex bilaterally as a main effect of the S conditions compared with the NS conditions. When SC fluency was compared with OS fluency, significant activations were found in anterior cingulate cortex bilaterally, the left inferior frontal gyrus, the middle frontal gyrus bilaterally, frontal operculum bilaterally and in the cerebellar vermis. These results support the hypothesis that superior posterior parietal cortex is a supramodal area implicated in task switching, even when no visual or spatial component is implicated in the tasks. Task switching, frequently used to examine 'frontal' executive functions, may also be clinically relevant to the assessment of patients with superior posterior parietal lesions.

Motor cortex involvement during verbal versus non-verbal lip and tongue movements

We evaluated left and right motor cortex involvement during verbal and non-verbal lip and tongue movements in seven healthy subjects using whole-head magnetoencephalography. The movements were paced by tone pips. The non-verbal tasks included a kissing movement and touching the teeth with the tongue. The verbal tasks comprised silent articulation of the Finnish vowel /o/, which requires mouth movement similar to that in the kissing task, pronouncing the same self-selected word repeatedly, and producing a new word for every tone pip. Motor cortex involvement was quantified by task-related suppression and subsequent rebound of the 20-Hz activity. The modulation concentrated to two sites along the central sulcus, identified as the motor face and hand representations. The 20-Hz suppression in the face area was relatively similar during all tasks. The post-movement rebound, however, was significantly left-lateralized during word production. In the non-verbal tasks, hand areas showed pronounced suppression of 20-Hz activity that was significantly diminished for the verbal tasks. The latencies of the 20-Hz suppression in the left and right face representations were correlated across subjects during verbal mouth movements. Increasing linguistic content of lip and tongue movements was thus manifested in spatially more focal motor cortex involvement, left-hemisphere lateralization of face area activation, and correlated timing across hemispheres.

Topographical layout of hand, eye, calculation, and language-related areas in the human parietal lobe

To identify subdivisions of the human parietal cortex, we collected fMRI data while ten subjects performed six tasks: grasping, pointing, saccades, attention, calculation, and phoneme detection. Examination of task intersections revealed a systematic anterior-to-posterior organization of activations associated with grasping only, grasping and pointing, all visuomotor tasks, attention and saccades, and saccades only. Calculation yielded two distinct activations: one unique to calculation in the bilateral anterior IPS mesial to the supramarginal gyrus and the other shared with phoneme detection in the left IPS mesial to the angular gyrus. These results suggest human homologs of the monkey areas AIP, MIP, V6A, and LIP and imply a large cortical expansion of the inferior parietal lobule correlated with the development of human language and calculation abilities.

Attentional selection and the processing of task-irrelevant information: insights from fMRI examinations of the Stroop task

In this chapter, we discuss our research that reveals how attentional mechanisms can modulate activity of posterior brain regions responsible for processing the unattended attribute of a stimulus. To do so, we utilized fMRI to reveal patterns of regional brain activity for variants of the Stroop task that differ in the nature of the task-irrelevant stimulus attribute. In all variants, individuals had to identify the ink color in which an item was presented. To vary attentional demands, we manipulated whether or not the task-irrelevant information contained conflicting color information. The variants differed in whether the conflicting color information was contained in a word naming a color (e.g. the word 'red' in blue ink), a word naming an object highly associated with a specific color (e.g. the word 'frog' in red ink), or a line drawing of an object highly associated with a specific color (e.g. a drawing of a frog in red ink). When the unattended stimulus attribute contained color information that conflicted with an item's ink color, increased activity was observed in the posterior brain region that processes the aspect of the task-irrelevant attribute related to color. Increased activity was observed in the left precuneus and left superior parietal cortex when the conflicting information arose from a color word; in the middle temporal gyrus and insular cortex when the word named an object highly associated with a specific color, and included extensive regions of early portions of the ventral visual processing stream when a line drawing was highly associated with a specific color. These areas have been implicated in word processing, semantic processing, and visual processing, respectively. Our results suggest that attentional selection can occur by: (1) increasing the gain on all posterior regions responsible for processing information related to the task demands, regardless of whether that information is contained in the task-relevant or task-irrelevant dimension; (2) limiting the processing of task-irrelevant information in order to reduce interference; and (3) modulating the processing of representations varying from those of a low-level perceptual nature up through those of a higher-order semantic nature.

Detecting latency differences in event-related BOLD responses: application to words versus nonwords and initial versus repeated face presentations

We introduce a new method for detecting differences in the latency of blood oxygenation level-dependent (BOLD) responses to brief events within the context of the General Linear Model. Using a first-order Taylor approximation in terms of the temporal derivative of a canonical hemodynamic response function, statistical parametric maps of differential latencies were estimated via the ratio of derivative to canonical parameter estimates. This method was applied to two example datasets: comparison of words versus nonwords in a lexical decision task and initial versus repeated presentations of faces in a fame-judgment task. Tests across subjects revealed both magnitude and latency differences within several brain regions. This approach offers a computationally efficient means of detecting BOLD latency differences over the whole brain. Precise characterization of the hemodynamic latency and its interpretation in terms of underlying neural differences remain problematic, however.

An auditory domain in primate prefrontal cortex

Although neuroimaging studies confirm the frontal lobe's involvement in language processes and auditory working memory, the cellular and network basis of these functions is unclear. Physiological studies of the frontal lobe in non-human primates have focused on visual working memory and auditory spatial processing in dorsolateral prefrontal cortex (PFC), although the candidate PFC areas for non-spatial acoustic processing lie in the ventrolateral PFC (areas 12 and 45), which receives afferents from physiologically and anatomically defined auditory cortex. We recorded neuronal responses from ventrolateral PFC to auditory cues in awake monkeys under controlled conditions and report that the macaque ventrolateral PFC contains an auditory responsive domain in which neurons show responses to complex sounds, including animal and human vocalizations.

How psychological science informs the teaching of reading

This monograph discusses research, theory, and practice relevant to how children learn to read English. After an initial overview of writing systems, the discussion summarizes research from developmental psychology on children's language competency when they enter school and on the nature of early reading development. Subsequent sections review theories of learning to read, the characteristics of children who do not learn to read (i.e., who have developmental dyslexia), research from cognitive psychology and cognitive neuroscience on skilled reading, and connectionist models of learning to read. The implications of the research findings for learning to read and teaching reading are discussed. Next, the primary methods used to teach reading (phonics and whole language) are summarized. The final section reviews laboratory and classroom studies on teaching reading. From these different sources of evidence, two inescapable conclusions emerge: (a) Mastering the alphabetic principle (that written symbols are associated with phonemes) is essential to becoming proficient in the skill of reading, and (b) methods that teach this principle directly are more effective than those that do not (especially for children who are at risk in some way for having difficulty learning to read). Using whole-language activities to supplement phonics instruction does help make reading fun and meaningful for children, but ultimately, phonics instruction is critically important because it helps beginning readers understand the alphabetic principle and learn new words. Thus, elementary-school teachers who make the alphabetic principle explicit are most effective in helping their students become skilled, independent readers.

The bilingual brain: cerebral representation of languages

The present article deals with theoretical and experimental aspects of language representation in the multilingual brain. Two general approaches were adopted in the study of the bilingual brain. The study of bilingual aphasics allows us to describe dissociations and double dissociations between the different subcomponents of the various languages. Furthermore, symptoms peculiar to bilingual aphasia were reported (pathological mixing and switching and translations disorders) which allowed the correlation of some abilities specific to bilinguals with particular neurofunctional systems. Another approach to the study of the bilingual brain is of the experimental type, such as electrophysiological investigations (electrocorticostimulation during brain surgery and event-related potentials) and functional neuroanatomy studies (positron emission tomography and functional magnetic resonance imaging). Functional neuroanatomy studies investigated the brain representation of languages when processing lexical and syntactic stimuli and short stories. Neurophysiologic and neuroimaging studies evidenced a similar cerebral representation of L1 and L2 lexicons both in early and late bilinguals. The representation of grammatical aspects of languages seems to be different between the two languages if L2 is acquired after the age of 7, with automatic processes and correctness being lower than those of the native language. These results are in line with a greater representation of the two lexicons in the declarative memory systems, whereas morphosyntactic aspects may be organized in different systems according to the acquisition vs learning modality.

Processing of irrelevant visual motion during performance of an auditory attention task

The extent to which irrelevant perception of visual motion distractors can be modulated by manipulating auditory load in a relevant task was assessed with Positron Emission Tomography (PET) and behavioural experiments. Subjects performed an auditory task and ignored an irrelevant visual motion stimulus, under two conditions. In a low load condition, subjects were asked to detect words spoken in a loud voice among words spoken in a quiet voice, while in a high load condition they attempted to detect bisyllabic words among monosyllabic and trisyllabic words. We found that motion-related visual areas were strongly activated by the irrelevant motion stimulus, compared to a static stimulus, under both conditions of load in the auditory task. In a second behavioural experiment, the duration of the motion after-effect was similarly unaffected by adaptation under low or high auditory load. These results are in clear contrast with the strong modulation of irrelevant motion processing by visual load, as reflected in the duration of the motion after effect (Section 6) and neural responses in motion-related visual areas (Rees et al., Science, (1997) 278, 338). These findings support the claim that attentional capacity is restricted within but not between sensory modalities, and indicate that processing of visual distractors may occur whenever there is sufficient visual capacity to process them, despite being task- and modality-irrelevant.

The effects of case mixing on word recognition: evidence from a PET study

The early stages of visual word recognition were investigated by scanning participants using PET as they took part in implicit and explicit reading tasks with visually disrupted stimuli. CaSe MiXiNg has been shown in behavioral studies to increase reaction times (RTs) in naming and other word recognition tasks. In this study, we found that during both an implicit (feature detection) task and an explicit word-naming task, mixed-case words compared to same-case words produced increased activation in an area of the right parietal cortex previously associated with visual attention. No effect of case was found in this area for pseudowords or consonant strings. Further, lowering the contrast of the stimuli slowed RTs as much as case mixing, but did not lead to the same increase in right parietal activation. No significant effect of case mixing was observed in left-hemisphere language areas. The results suggest that reading mixed-case words requires increased attentional processing. However, later word recognition processes may be relatively unaffected by the disruption in presentation.

Ideographic characters call for extra processing to correspond with phonemes

Cortical areas used in the copying of Japanese ideographic characters and syllabic characters were studied using functional magnetic resonance imaging in healthy volunteers. Complexity of characters was controlled to illustrate differences resulting from character to sound conversion differences between the ideographic and syllabic characters. Statistical comparisons indicated extensive activation in the fusiform gyrus, posterior portions around the intraparietal sulcus and in the conjunction area of BA 6, 9 and 44 (which is assumed to be Exner's area) during the copying of ideographic characters. These findings suggested that indirectness between ideographic characters and their pronunciation demands extra processing such as semantic mediation and intensive grapheme processing in comparison with syllabic characters.

Differences in auditory processing of words and pseudowords: an fMRI study

Although there has been great interest in the neuroanatomical basis of reading, little attention has been focused on auditory language processing. The purpose of this study was to examine the differential neuroanatomical response to the auditory processing of real words and pseudowords. Eight healthy right-handed participants performed two phoneme monitoring tasks (one with real word stimuli and one with pseudowords) during a functional magnetic resonance imaging (fMRI) scan with a 4.1 T system. Both tasks activated the inferior frontal gyrus (IFG), the posterior superior temporal gyrus (pSTG) and the inferior parietal lobe (IPL). Pseudoword processing elicited significantly more activation within the posterior cortical regions compared with real word processing. Previous reading studies have suggested that this increase is due to an increased demand on the lexical access system. The left inferior frontal gyrus, on the other hand, did not reveal a significant difference in the amount of activation as a function of stimulus type. The lack of a differential response in IFG for auditory processing supports its hypothesized involvement in grapheme to phoneme conversion processes. These results are consistent with those from previous neuroimaging reading studies and emphasize the utility of examining both input modalities (e.g., visual or auditory) to compose a more complete picture of the language network.

Phonological processing in visual rhyming: a developmental erp study

We employed a visual rhyming priming paradigm to characterize the development of brain systems important for phonological processing in reading. We studied 109 righthanded, native English speakers within eight age groups: 7-8, 9-10, 11-12, 13-14, 15-16, 17-18, 19-20, and 21-23. Participants decided whether two written words (prime-target) rhymed (JUICE-MOOSE) or not (CHAIR-MOOSE). In similar studies of adults, two main event-related potential (ERP) effects have been described: a negative slow wave to primes, larger over anterior regions of the left hemisphere and hypothesized to index rehearsal of the primes, and a negative deflection to targets, peaking at 400-450 msec, maximal over right temporal-parietal regions, larger for nonrhyming than rhyming targets, and hypothesized index phonological matching. In this study, these two ERP effects were observed in all age groups; however, the two effects showed different developmental timecourses. On the one hand, the frontal asymmetry to primes increased with age; moreover, this asymmetry was correlated with reading and spelling scores, even after controlling for age. On the other hand, the distribution and onset of the more posterior rhyming effect (RE) were stable across age groups, suggesting that phonological matching relied on similar neural systems across these ages. Behaviorally, both reaction times and accuracy improved with age. These results suggest that different aspects of phonological processing rely on different neural systems that have different to developmental timecourses.