Reading aloud boosts connectivity through the putamen

Functional neuroimaging and lesion studies have frequently reported thalamic and putamen activation during reading and speech production. However, it is currently unknown how activity in these structures interacts with that in other reading and speech production areas. This study investigates how reading aloud modulates the neuronal interactions between visual recognition and articulatory areas, when both the putamen and thalamus are explicitly included. Using dynamic causal modeling in skilled readers who were reading regularly spelled English words, we compared 27 possible pathways that might connect the ventral anterior occipito-temporal sulcus (aOT) to articulatory areas in the precentral cortex (PrC). We focused on whether the neuronal interactions within these pathways were increased by reading relative to picture naming and other visual and articulatory control conditions. The results provide strong evidence that reading boosts the aOT–PrC pathway via the putamen but not the thalamus. However, the putamen pathway was not exclusive because there was also evidence for another reading pathway that did not involve either the putamen or the thalamus. We conclude that the putamen plays a special role in reading but this is likely to vary with individual reading preferences and strategies.

The impact of second language learning on semantic and nonsemantic first language reading

The relationship between orthography (spelling) and phonology (speech sounds) varies across alphabetic languages. Consequently, learning to read a second alphabetic language, that uses the same letters as the first, increases the phonological associations that can be linked to the same orthographic units. In subjects with English as their first language, previous functional imaging studies have reported increased left ventral prefrontal activation for reading words with spellings that are inconsistent with their orthographic neighbors (e.g., PINT) compared with words that are consistent with their orthographic neighbors (e.g., SHIP). Here, using functional magnetic resonance imaging (fMRI) in 17 Italian–English and 13 English–Italian bilinguals, we demonstrate that left ventral prefrontal activation for first language reading increases with second language vocabulary knowledge. This suggests that learning a second alphabetic language changes the way that words are read in the first alphabetic language. Specifically, first language reading is more reliant on both lexical/semantic and nonlexical processing when new orthographic to phonological mappings are introduced by second language learning. Our observations were in a context that required participants to switch between languages. They motivate future fMRI studies to test whether first language reading is also altered in contexts when the second language is not in use.

Integrating visual and tactile information in the perirhinal cortex

By virtue of its widespread afferent projections, perirhinal cortex is thought to bind polymodal information into abstract object-level representations. Consistent with this proposal, deficits in cross-modal integration have been reported after perirhinal lesions in nonhuman primates. It is therefore surprising that imaging studies of humans have not observed perirhinal activation during visual–tactile object matching. Critically, however, these studies did not differentiate between congruent and incongruent trials. This is important because successful integration can only occur when polymodal information indicates a single object (congruent) rather than different objects (incongruent). We scanned neurologically intact individuals using functional magnetic resonance imaging (fMRI) while they matched shapes. We found higher perirhinal activation bilaterally for cross-modal (visual–tactile) than unimodal (visual–visual or tactile–tactile) matching, but only when visual and tactile attributes were congruent. Our results demonstrate that the human perirhinal cortex is involved in cross-modal, visual–tactile, integration and, thus, indicate a functional homology between human and monkey perirhinal cortices.

The main sources of intersubject variability in neuronal activation for reading aloud

The aim of this study was to find the most prominent source of intersubject variability in neuronal activation for reading familiar words aloud. To this end, we collected functional imaging data from a large sample of subjects (n = 76) with different demographic characteristics such as handedness, sex, and age, while reading. The subject-by-subject error variance was estimated from a one-sample t test (on all 76 subjects) and was reduced to a lower dimension using principal components decomposition. A Gaussian Mixture Model was then applied to dissociate different subgroups of subjects that explained the main sources of variability in the data. This resulted in the identification of four different subject groups. The comparison of these subgroups to the subjects' demographic details showed that age had a significant effect on the subject partitioning. In addition, a region-by-group dissociation in the dorsal and the ventral inferior frontal cortex was consistent with previously reported dissociations in semantic and nonsemantic reading strategies. In contrast to these significant findings, the groupings did not differentiate subjects on the basis of either sex or handedness, nor did they segregate the subjects with right- versus left-lateralized reading activation. We therefore conclude that, of the variables tested, age and reading strategy were the most prominent source of variability in activation for reading familiar words aloud.

Structural correlates of semantic and phonemic fluency ability in first and second languages

Category and letter fluency tasks are commonly used clinically to investigate the semantic and phonological processes central to speech production, but the neural correlates of these processes are difficult to establish with functional neuroimaging because of the relatively unconstrained nature of the tasks. This study investigated whether differential performance on semantic (category) and phonemic (letter) fluency in neurologically normal participants was reflected in regional gray matter density. The participants were 59 highly proficient speakers of 2 languages. Our findings corroborate the importance of the left inferior temporal cortex in semantic relative to phonemic fluency and show this effect to be the same in a first language (L1) and second language (L2). Additionally, we show that the pre-supplementary motor area (pre-SMA) and head of caudate bilaterally are associated with phonemic more than semantic fluency, and this effect is stronger for L2 than L1 in the caudate nuclei. To further validate these structural results, we reanalyzed previously reported functional data and found that pre-SMA and left caudate activation was higher for phonemic than semantic fluency. On the basis of our findings, we also predict that lesions to the pre-SMA and caudate nuclei may have a greater impact on phonemic than semantic fluency, particularly in L2 speakers.

Dissociating verbal and nonverbal audiovisual object processing

This fMRI study investigates how audiovisual integration differs for verbal stimuli that can be matched at a phonological level and nonverbal stimuli that can be matched at a semantic level. Subjects were presented simultaneously with one visual and one auditory stimulus and were instructed to decide whether these stimuli referred to the same object or not. Verbal stimuli were simultaneously presented spoken and written object names, and nonverbal stimuli were photographs of objects simultaneously presented with naturally occurring object sounds. Stimulus differences were controlled by including two further conditions that paired photographs of objects with spoken words and object sounds with written words. Verbal matching, relative to all other conditions, increased activation in a region of the left superior temporal sulcus that has previously been associated with phonological processing. Nonverbal matching, relative to all other conditions, increased activation in a right fusiform region that has previously been associated with structural and conceptual object processing. Thus, we demonstrate how brain activation for audiovisual integration depends on the verbal content of the stimuli, even when stimulus and task processing differences are controlled.

Selective activation around the left occipito-temporal sulcus for words relative to pictures: individual variability or false positives?

We used high‐resolution fMRI to investigate claims that learning to read results in greater left occipito‐temporal (OT) activation for written words relative to pictures of objects. In the first experiment, 9/16 subjects performing a one‐back task showed activation in ≥1 left OT voxel for words relative to pictures (P < 0.05 uncorrected). In a second experiment, another 9/15 subjects performing a semantic decision task activated ≥1 left OT voxel for words relative to pictures. However, at this low statistical threshold false positives need to be excluded. The semantic decision paradigm was therefore repeated, within subject, in two different scanners (1.5 and 3 T). Both scanners consistently localised left OT activation for words relative to fixation and pictures relative to words, but there were no consistent effects for words relative to pictures. Finally, in a third experiment, we minimised the voxel size (1.5 × 1.5 × 1.5 mm³) and demonstrated a striking concordance between the voxels activated for words and pictures, irrespective of task (naming vs. one‐back) or script (English vs. Hebrew). In summary, although we detected differential activation for words relative to pictures, these effects: (i) do not withstand statistical rigour; (ii) do not replicate within or between subjects; and (iii) are observed in voxels that also respond to pictures of objects. Our findings have implications for the role of left OT activation during reading. More generally, they show that studies using low statistical thresholds in single subject analyses should correct the statistical threshold for the number of comparisons made or replicate effects within subject. Hum Brain Mapp 2008. © 2007 Wiley‐Liss, Inc.

The subfornical organ: a central nervous system site for actions of circulating leptin

Adipose tissue plays a critical role in energy homeostasis, secreting adipokines that control feeding, thermogenesis, and neuroendocrine function. Leptin is the prototypic adipokine that acts centrally to signal long-term energy balance. While hypothalamic and brain stem nuclei are well-established sites of action of leptin, we tested the hypothesis that leptin signaling occurs in the subfornical organ (SFO). The SFO is a circumventricular organ (CVO) that lacks the normal blood-brain barrier, is an important site in central autonomic regulation, and has been suggested to have a role in modulating peripheral signals indicating energy status. We report here the presence of mRNA for the signaling form of the leptin receptor in SFO and leptin receptor localization by immunohistochemistry within this CVO. Central administration of leptin resulted in phosphorylation of STAT3 in neurons of SFO. Whole cell current-clamp recordings from dissociated SFO neurons demonstrated that leptin (10 nM) influenced the excitability of 64% (46/72) of SFO neurons. Leptin was found to depolarize the majority of responsive neurons with a mean change in membrane potential of 7.3 +/- 0.6 mV (39% of all SFO neurons), while the remaining cells that responded to leptin hyperpolarized (-6.9 +/- 0.7 mV, 25% of all SFO neurons). Similar depolarizing and hyperpolarizing effects of leptin were observed in recordings from acutely prepared SFO slice preparations. Leptin was found to influence the same population of SFO neurons influenced by amylin as three of four cells tested for the effects of bath application of both amylin and leptin depolarized to both peptides. These observations identify the SFO as a possible central nervous system location, with direct access to the peripheral circulation, at which leptin may act to influence hypothalamic control of energy homeostasis.

Inter-subject variability in the use of two different neuronal networks for reading aloud familiar words

Cognitive models of reading predict that high frequency regular words can be read in more than one way. We investigated this hypothesis using functional MRI and covariance analysis in 43 healthy skilled readers. Our results dissociated two sets of regions that were differentially engaged across subjects who were reading the same familiar words. Some subjects showed more activation in left inferior frontal and anterior occipito-temporal regions while other subjects showed more activation in right inferior parietal and left posterior occipito-temporal regions. To explore the behavioural correlates of these systems, we measured the difference between reading speed for irregularly spelled words relative to pseudowords outside the scanner in fifteen of our subjects and correlated this measure with fMRI activation for reading familiar words. The faster the lexical reading the greater the activation in left posterior occipito-temporal and right inferior parietal regions. Conversely, the slower the lexical reading the greater the activation in left anterior occipito-temporal and left ventral inferior frontal regions. Thus, the double dissociation in irregular and pseudoword reading behaviour predicted the double dissociation in neuronal activation for reading familiar words. We discuss the implications of these results which may be important for understanding how reading is learnt in childhood or re-learnt following brain damage in adulthood.

The influence of colour and sound on neuronal activation during visual object naming

This paper investigates how neuronal activation for naming photographs of objects is influenced by the addition of appropriate colour or sound. Behaviourally, both colour and sound are known to facilitate object recognition from visual form. However, previous functional imaging studies have shown inconsistent effects. For example, the addition of appropriate colour has been shown to reduce antero-medial temporal activation whereas the addition of sound has been shown to increase posterior superior temporal activation. Here we compared the effect of adding colour or sound cues in the same experiment. We found that the addition of either the appropriate colour or sound increased activation for naming photographs of objects in bilateral occipital regions and the right anterior fusiform. Moreover, the addition of colour reduced left antero-medial temporal activation but this effect was not observed for the addition of object sound. We propose that activation in bilateral occipital and right fusiform areas precedes the integration of visual form with either its colour or associated sound. In contrast, left antero-medial temporal activation is reduced because object recognition is facilitated after colour and form have been integrated.

The role of the posterior superior temporal sulcus in audiovisual processing

In this study we investigate previous claims that a region in the left posterior superior temporal sulcus (pSTS) is more activated by audiovisual than unimodal processing. First, we compare audiovisual to visual-visual and auditory-auditory conceptual matching using auditory or visual object names that are paired with pictures of objects or their environmental sounds. Second, we compare congruent and incongruent audiovisual trials when presentation is simultaneous or sequential. Third, we compare audiovisual stimuli that are either verbal (auditory and visual words) or nonverbal (pictures of objects and their associated sounds). The results demonstrate that, when task, attention, and stimuli are controlled, pSTS activation for audiovisual conceptual matching is 1) identical to that observed for intramodal conceptual matching, 2) greater for incongruent than congruent trials when auditory and visual stimuli are simultaneously presented, and 3) identical for verbal and nonverbal stimuli. These results are not consistent with previous claims that pSTS activation reflects the active formation of an integrated audiovisual representation. After a discussion of the stimulus and task factors that modulate activation, we conclude that, when stimulus input, task, and attention are controlled, pSTS is part of a distributed set of regions involved in conceptual matching, irrespective of whether the stimuli are audiovisual, auditory-auditory or visual-visual.

Vowel-specific mismatch responses in the anterior superior temporal gyrus: an fMRI study

There have been many functional imaging studies that have investigated the neural correlates of speech perception by contrasting neural responses to speech and "speech-like" but unintelligible control stimuli. A potential drawback of this approach is that intelligibility is necessarily conflated with a change in the acoustic parameters of the stimuli. The approach we have adopted is to take advantage of the mismatch response elicited by an oddball paradigm to probe neural responses in temporal lobe structures to a parametrically varied set of deviants in order to identify brain regions involved in vowel processing. Thirteen normal subjects were scanned using a functional magnetic resonance imaging (fMRI) paradigm while they listened to continuous trains of auditory stimuli. Three classes of stimuli were used: 'vowel deviants' and two classes of control stimuli: one acoustically similar ('single formants') and the other distant (tones). The acoustic differences between the standard and deviants in both the vowel and single-formant classes were designed to match each other closely. The results revealed an effect of vowel deviance in the left anterior superior temporal gyrus (aSTG). This was most significant when comparing all vowel deviants to standards, irrespective of their psychoacoustic or physical deviance. We also identified a correlation between perceptual discrimination and deviant-related activity in the dominant superior temporal sulcus (STS), although this effect was not stimulus specific. The responses to vowel deviants were in brain regions implicated in the processing of intelligible or meaningful speech, part of the so-called auditory "what" processing stream. Neural components of this pathway would be expected to respond to sudden, perhaps unexpected changes in speech signal that result in a change to narrative meaning.

Nesfatin-1 influences the excitability of paraventricular nucleus neurones

Nesfatin-1 is a newly-discovered satiety peptide found in several nuclei of the hypothalamus, including the paraventricular nucleus. To begin to understand the physiological mechanisms underlying these satiety-inducing actions, we examined the effects of nesfatin-1 on the excitability of neurones in the paraventricular nucleus. Whole-cell current-clamp recordings from rat paraventricular nucleus neurones showed nesfatin-1 to have either hyperpolarizing or depolarising effects on the majority of neurones tested. Both types of response were observed in neurones irrespective of classification based on electrophysiological fingerprint (magnocellular, neuroendocrine or pre-autonomic) or molecular phenotype (vasopressin, oxytocin, corticotrophin-releasing hormone, thyrotrophin-releasing hormone or vesicular glutamate transporter), determined using single cell reverse transcription-polymerase chain reaction. Consequently, we provide the first evidence that this peptide, which is produced in the paraventricular nucleus, has effects on the membrane potential of a large proportion of different subpopulations of neurones located in this nucleus, and therefore identify nesfatin-1 as a potentially important regulator of paraventricular nucleus output.

Brain activation for consonants and vowels

Previous behavioral and electrophysiological studies have shown dissociation between consonants and vowels. We used functional magnetic resonance imaging to investigate whether vowel and consonant processing differences are expressed in the neuronal activation pattern and whether they are modulated by task. The experimental design involved reading aloud and lexical decision on visually presented pseudowords created by transposing or replacing consonants or vowels in words. During reading aloud, changing vowels relative to consonants increased activation in a right middle temporal area previously associated with prosodic processing of speech input. In contrast, during lexical decision, changing consonants relative to vowels increased activation in a right middle frontal area associated with inhibiting go-responses. The task-sensitive nature of these effects demonstrates that consonants and vowels differ at a processing, rather than stimulus, level. We argue that prosodic processing of vowel changes arise during self-monitoring of speech output, whereas greater inhibition of go-responses to consonant changes follows insufficient lexico-semantic processing when nonwords looking particularly like words must be rejected. Our results are consistent with claims that vowels and consonants place differential demands on prosodic and lexico-semantic processing, respectively. They also highlight the different types of information that can be drawn from functional imaging and neuropsychological studies.

Perirhinal contributions to human visual perception

Medial temporal lobe (MTL) structures including the hippocampus, entorhinal cortex, and perirhinal cortex are thought to be part of a unitary system dedicated to memory [1, 2], although recent studies suggest that at least one component—perirhinal cortex—might also contribute to perceptual processing [3–6]. To date, the strongest evidence for this comes from animal lesion studies [7–14]. In contrast, the findings from human patients with naturally occurring MTL lesions are less clear and suggest a possible functional difference between species [15–20]. Here, both these issues were addressed with functional neuroimaging in healthy volunteers performing a perceptual discrimination task originally developed for monkeys [7]. This revealed perirhinal activation when the task required the integration of visual features into a view-invariant representation but not when it could be accomplished on the basis of simple features (e.g., color and shape). This activation pattern matched lateral inferotemporal regions classically associated with visual processing but differed from entorhinal cortex associated with memory encoding. The results demonstrate a specific role for the perirhinal cortex in visual perception and establish a functional homology for perirhinal cortex between species, although we propose that in humans, the region contributes to a wider behavioral repertoire including mnemonic, perceptual, and linguistic processes.

The Effect of Prior Visual Information on Recognition of Speech and Sounds

To identify and categorize complex stimuli such as familiar objects or speech, the human brain integrates information that is abstracted at multiple levels from its sensory inputs. Using cross-modal priming for spoken words and sounds, this functional magnetic resonance imaging study identified 3 distinct classes of visuoauditory incongruency effects: visuoauditory incongruency effects were selective for 1) spoken words in the left superior temporal sulcus (STS), 2) environmental sounds in the left angular gyrus (AG), and 3) both words and sounds in the lateral and medial prefrontal cortices (IFS/mPFC). From a cognitive perspective, these incongruency effects suggest that prior visual information influences the neural processes underlying speech and sound recognition at multiple levels, with the STS being involved in phonological, AG in semantic, and mPFC/IFS in higher conceptual processing. In terms of neural mechanisms, effective connectivity analyses (dynamic causal modeling) suggest that these incongruency effects may emerge via greater bottom-up effects from early auditory regions to intermediate multisensory integration areas (i.e., STS and AG). This is consistent with a predictive coding perspective on hierarchical Bayesian inference in the cortex where the domain of the prediction error (phonological vs. semantic) determines its regional expression (middle temporal gyrus/STS vs. AG/intraparietal sulcus).

Prevalence ofCampylobacterand four endoparasites in dog populations associated with Hearing Dogs

OBJECTIVES

This study established the prevalence of four gastrointestinal parasites (Isopora species, Giardia species, Uncinaria stenocephala, Toxocara canis) and one bacterial infection (Campylobacter jejuni/coli) in dogs associated with the charity Hearing Dogs for Deaf People.

METHODS

Dogs' faeces were routinely sampled from dogs according to whether they were in Socialising, Kennelling or Visiting the Hearing Dogs site. A further group consisted of dogs with diarrhoea.

RESULTS

Prevalence rates for dogs in Socialising (n=326), Kennelling (n=117), Visiting (n=106) and Diarrhoea (n=59) groups, respectively, were as follows: Campylobacter- 26, 21, 15 and 31 per cent; Coccidia - 3, 0, 0 and 2 per cent; Giardia- 13, 3, 2 and 10 per cent; hookworm - 1, 1, 4 and 5 per cent; and Toxocara- 4, 2, 3 and 2 per cent. There were significant differences in the levels of Giardia and hookworm found between the four different groups of dogs. No significant gender differences were found, and dogs that were positive for Campylobacter in the Visiting group were significantly younger.

CLINICAL SIGNIFICANCE

This study provides current information on the infection rates in specific dog populations in the UK. This is relevant to the veterinary health of dogs and the possible risk of zoonotic infection to humans.

Exploring cross-linguistic vocabulary effects on brain structures using voxel-based morphometry

Given that there are neural markers for the acquisition of a non-verbal skill, we review evidence of neural markers for the acquisition of vocabulary. Acquiring vocabulary is critical to learning one's native language and to learning other languages. Acquisition requires the ability to link an object concept (meaning) to sound. Is there a region sensitive to vocabulary knowledge? For monolingual English speakers, increased vocabulary knowledge correlates with increased grey matter density in a region of the parietal cortex that is well-located to mediate an association between meaning and sound (the posterior supramarginal gyrus). Further this region also shows sensitivity to acquiring a second language. Relative to monolingual English speakers, Italian-English bilinguals show increased grey matter density in the same region.Differences as well as commonalities might exist in the neural markers for vocabulary where lexical distinctions are also signalled by tone. Relative to monolingual English, Chinese multilingual speakers, like European multilinguals, show increased grey matter density in the parietal region observed previously. However, irrespective of ethnicity, Chinese speakers (both Asian and European) also show highly significant increased grey matter density in two right hemisphere regions (the superior temporal gyrus and the inferior frontal gyrus). They also show increased grey matter density in two left hemisphere regions (middle temporal and superior temporal gyrus). Such increases may reflect additional resources required to process tonal distinctions for lexical purposes or to store tonal differences in order to distinguish lexical items. We conclude with a discussion of future lines of enquiry.

Dissociating stimulus-driven semantic and phonological effect during reading and naming

The aim of the present study was to dissociate the neural correlates of semantic and phonological processes during word reading and picture naming. Previous studies have addressed this issue by contrasting tasks involving semantic and phonological decisions. However, these tasks engage verbal short‐term memory and executive functions that are not required for reading and naming. Here, 20 subjects were instructed to overtly name written words and pictures of objects while their neuronal responses were measured using functional magnetic resonance imaging (fMRI). Each trial consisted of a pair of successive stimuli that were either semantically related (e.g., “ROBIN‐nest”), phonologically related (e.g., “BELL‐belt”), unrelated (e.g., “KITE‐lobster”), or semantically and phonologically identical (e.g., “FRIDGE‐fridge”). In addition, a pair of stimuli could be presented in either the same modality (word‐word or picture‐picture) or a different modality (word‐picture or picture‐word). We report that semantically related pairs modulate neuronal responses in a left‐lateralized network, including the pars orbitalis of the inferior frontal gyrus, the middle temporal gyrus, the angular gyrus, and the superior frontal gyrus. We propose that these areas are involved in stimulus‐driven semantic processes. In contrast, phonologically related pairs modulate neuronal responses in bilateral insula. This region is therefore implicated in the discrimination of similar, competing phonological and articulatory codes. The above effects were detected with both words and pictures and did not differ between the two modalities even with a less conservative statistical threshold. In conclusion, this study dissociates the effects of semantic and phonological relatedness between successive items during reading and naming aloud. Hum Brain Mapp, 2007. © 2006 Wiley‐Liss, Inc.

Detecting subject-specific activations using fuzzy clustering

Inter-subject variability in evoked brain responses is attracting attention because it may reflect important variability in structure–function relationships over subjects. This variability could be a signature of degenerate (many-to-one) structure–function mappings in normal subjects or reflect changes that are disclosed by brain damage. In this paper, we describe a non-iterative fuzzy clustering algorithm (FCP: fuzzy clustering with fixed prototypes) for characterizing inter-subject variability in between-subject or second-level analyses of fMRI data. The approach identifies the contribution of each subject to response profiles in voxels surviving a classical F-statistic criterion. The output identifies subjects who drive activation in specific cortical regions (local effects) or in voxels distributed across neural systems (global effects). The sensitivity of the approach was assessed in 38 normal subjects performing an overt naming task. FCP revealed that several subjects had either abnormally high or abnormally low responses. FCP may be particularly useful for characterizing outlier responses in rare patients or heterogeneous populations. In these cases, atypical activations may not be detected by standard tests, under parametric assumptions. The advantage of using FCP is that it searches all voxels systematically and can identify atypical activation patterns in a quantitative and unsupervised manner.

Anatomical traces of vocabulary acquisition in the adolescent brain

A surprising discovery in recent years is that the structure of the adult human brain changes when a new cognitive or motor skill is learned. This effect is seen as a change in local gray or white matter density that correlates with behavioral measures. Critically, however, the cognitive and anatomical mechanisms underlying these learning-related structural brain changes remain unknown. Here, we combined brain imaging, detailed behavioral analyses, and white matter tractography in English-speaking monolingual adolescents to show that a critical linguistic prerequisite (namely, knowledge of vocabulary) is proportionately related to relative gray matter density in bilateral posterior supramarginal gyri. The effect was specific to the number of words learned, regardless of verbal fluency or other cognitive abilities. The identified region was found to have direct connections to other inferior parietal areas that separately process either the sounds of words or their meanings, suggesting that the posterior supramarginal gyrus plays a role in linking the basic components of vocabulary knowledge. Together, these analyses highlight the cognitive and anatomical mechanisms that mediate an essential language skill.

Anterior temporal cortex and semantic memory: reconciling findings from neuropsychology and functional imaging

Studies of semantic impairment arising from brain disease suggest that the anterior temporal lobes are critical for semantic abilities in humans; yet activation of these regions is rarely reported in functional imaging studies of healthy controls performing semantic tasks. Here, we combined neuropsychological and PET functional imaging data to show that when healthy subjects identify concepts at a specific level, the regions activated correspond to the site of maximal atrophy in patients with relatively pure semantic impairment. The stimuli were color photographs of common animals or vehicles, and the task was category verification at specific (e.g., robin), intermediate (e.g., bird), or general (e.g., animal) levels. Specific, relative to general, categorization activated the antero-lateral temporal cortices bilaterally, despite matching of these experimental conditions for difficulty. Critically, in patients with atrophy in precisely these areas, the most pronounced deficit was in the retrieval of specific semantic information.

Brain Activation for Lexical Decision and Reading Aloud: Two Sides of the Same Coin?

This functional magnetic resonance imaging study compared the neuronal implementation of word and pseudoword processing during two commonly used word recognition tasks: lexical decision and reading aloud. In the lexical decision task, participants made a finger-press response to indicate whether a visually presented letter string is a word or a pseudoword (e.g., “paple”). In the reading-aloud task, participants read aloud visually presented words and pseudowords. The same sets of words and pseudowords were used for both tasks. This enabled us to look for the effects of task (lexical decision vs. reading aloud), lexicality (words vs. nonwords), and the interaction of lexicality with task. We found very similar patterns of activation for lexical decision and reading aloud in areas associated with word recognition and lexical retrieval (e.g., left fusiform gyrus, posterior temporal cortex, pars opercularis, and bilateral insulae), but task differences were observed bilaterally in sensorimotor areas. Lexical decision increased activation in areas associated with decision making and finger tapping (bilateral postcentral gyri, supplementary motor area, and right cerebellum), whereas reading aloud increased activation in areas associated with articulation and hearing the sound of the spoken response (bilateral precentral gyri, superior temporal gyri, and posterior cerebellum). The effect of lexicality (pseudoword vs. words) was also remarkably consistent across tasks. Nevertheless, increased activation for pseudowords relative to words was greater in the left precentral cortex for reading than lexical decision, and greater in the right inferior frontal cortex for lexical decision than reading. We attribute these effects to differences in the demands on speech production and decision-making processes, respectively.