Auditory and visual word processing studied with fMRI

Brain activations associated with semantic processing of visual and auditory words were investigated using functional magnetic resonance imaging (fMRI). For each form of word presentation, subjects performed two tasks: one semantic, and one nonsemantic. The semantic task was identical for both auditory and visual presentation: single words were presented and subjects determined whether the word was concrete or abstract. In the nonsemantic task for auditory words, subjects determined whether the word had one syllable or multiple syllables. In the nonsemantic task for visual words, subjects determined whether the word was presented in lower case or upper case. There was considerable overlap in where auditory and visual word semantic processing occurred. Visual and auditory semantic tasks both activated the left inferior frontal (BA 45), bilateral anterior prefrontal (BA 10, 46), and left premotor regions (BA 6) and anterior SMA (BA 6, 8). Left posterior temporal (middle temporal and fusiform gyrus) and predominantly right-sided cerebellar activations were observed during the auditory semantic task but were not above threshold during visual word presentation. The data, when averaged across subjects, did not show obligatory activation of left inferior frontal and temporal language areas during nonsemantic word tasks. Individual subjects showed differences in the activation of the inferior frontal region while performing the same task, even though they showed similar response latency and accuracy.     

Germ-line therapy for mitochondrial disease: some ethical objections

In an effort to examine the functional neuroanatomy of semantic memory, we studied the relative cerebral blood flow of eight healthy young subjects using 15O-water positron emission tomography (PET). Relative to a visual baseline control condition, each of four visual matching-to-sample tasks activated components of the ventral visual processing stream, including the inferior occipital and temporal cortices. Contrasting the task with the highest semantic component, a variation on the Pyramids and Palm Trees paradigm, with a size discrimination task resulted in focal activation in the anterior inferior temporal lobe, focused in the parahippocampal gyrus. There was additional activation in BA47 of the inferior frontal cortex. These data replicate and extend previously reported results using similar paradigms, and are consistent with cognitive neuropsychological models that stress the executive role of BA47 in semantic processing tasks.     

An MEG study of picture naming

The purpose of this study was to relate a psycholinguistic processing model of picture naming to the dynamics of cortical activation during picture naming. The activation was recorded from eight Dutch subjects with a whole-head neuromagnetometer. The processing model, based on extensive naming latency studies, is a stage model. In preparing a picture"s name, the speaker performs a chain of specific operations. They are, in this order, computing the visual percept, activating an appropriate lexical concept, selecting the target word from the mental lexicon, phonological encoding, phonetic encoding, and initiation of articulation. The time windows for each of these operations are reasonably well known and could be related to the peak activity of dipole sources in the individual magnetic response patterns. The analyses showed a clear progression over these time windows from early occipital activation, via parietal and temporal to frontal activation. The major specific findings were that (1) a region in the left posterior temporal lobe, agreeing with the location of Wernicke"s area, showed prominent activation starting about 200 msec after picture onset and peaking at about 350 msec (i.e., within the stage of phonological encoding), and (2) a consistent activation was found in the right parietal cortex, peaking at about 230 msec after picture onset, thus preceding and partly overlapping with the left temporal response. An interpretation in terms of the management of visual attention is proposed.     

Cerebral cortical hyperactivation in response to mental stress in patients with coronary artery disease

The central nervous system (CNS) effects of mental stress in patients with coronary artery disease (CAD) are unexplored. The present study used positron emission tomography (PET) to measure brain correlates of mental stress induced by an arithmetic serial subtraction task in CAD and healthy subjects. Mental stress resulted in hyperactivation in CAD patients compared with healthy subjects in several brain areas including the left parietal cortex [angular gyrus/parallel sulcus (area 39)], left anterior cingulate (area 32), right visual association cortex (area 18), left fusiform gyrus, and cerebellum. These same regions were activated within the CAD patient group during mental stress versus control conditions. In the group of healthy subjects, activation was significant only in the left inferior frontal gyrus during mental stress compared with counting control. Decreases in blood flow also were produced by mental stress in CAD versus healthy subjects in right thalamus (lateral dorsal, lateral posterior), right superior frontal gyrus (areas 32, 24, and 10), and right middle temporal gyrus (area 21) (in the region of the auditory association cortex). Of particular interest, a subgroup of CAD patients that developed painless myocardial ischemia during mental stress had hyperactivation in the left hippocampus and inferior parietal lobule (area 40), left middle (area 10) and superior frontal gyrus (area 8), temporal pole, and visual association cortex (area 18), and a concomitant decrease in activation observed in the anterior cingulate bilaterally, right middle and superior frontal gyri, and right visual association cortex (area 18) compared with CAD patients without myocardial ischemia. These findings demonstrate an exaggerated cerebral cortical response and exaggerated asymmetry to mental stress in individuals with CAD.     

Cognitive neuropsychological analysis and neuroanatomic correlates in a case of acute anomia

We describe an analysis of lexical processing performed in a patient with the acute onset of an isolated anomia. Based on a model of lexical processing, we evaluated hypotheses as to the source of the naming deficit. We observed impairments in oral and written picture naming and oral naming to definition with relatively intact semantic processing across input modalities, suggesting that output from the semantic system was impaired. In contrast to previous reports, we propose that this pattern represents an impairment that arises late in semantic processing prior to accessing mode-specific verbal and graphemic output lexicons. These deficits were associated with a lesion in the posterior portion of the middle temporal gyrus or area 37, an area of supramodal association cortex that is uniquely suited as a substrate for the multimodal deficit in naming.     

Neural correlates of semantic and episodic memory retrieval

To investigate the functional neuroanatomy associated with retrieving semantic and episodic memories, we measured changes in regional cerebral blood flow (rCBF) with positron emission tomography (PET) while subjects generated single word responses to achromatic line drawings of objects. During separate scans, subjects either named each object, retrieved a commonly associated color of each object (semantic condition), or recalled a previously studied uncommon color of each object (episodic condition). Subjects were also scanned while staring at visual noise patterns to provide a low level perceptual baseline. Relative to the low level baseline, all three conditions revealed bilateral activations of posterior regions of the temporal lobes, cerebellum, and left lateralized activations in frontal regions. Retrieving semantic information, as compared to object naming, activated left inferior temporal, left superior parietal, and left frontal cortices. In addition, small regions of right frontal cortex were activated. Retrieving episodic information, as compared to object naming, activated bilateral medial parietal cortex, bilateral retrosplenial cortex, right frontal cortex, thalamus, and cerebellum. Direct comparison of the semantic and episodic conditions revealed bilateral activation in temporal and frontal lobes in the semantic task (left greater than right), and activation in medial parietal cortex, retrosplenial cortex, thalamus, and cerebellum (but not right frontal regions) in the episodic task. These results support the assertion that distinct neural structures mediate semantic and episodic memory retrieval. However, they also raise questions regarding the specific roles of left temporal and right frontal cortices during episodic memory retrieval, in particular.     

Vowel Duration Affects Visual Word Identification: Evidence That the Mediating Phonology Is Phonetically Informed.

What form is the lexical phonology that gives rise to phonological effects in visual lexical decision? The authors explored the hypothesis that beyond phonological contrasts the physical phonetic details of words are included. Three experiments using lexical decision and 1 using naming compared processing times for printed words (e.g., plead and pleat) that differ, when spoken, in vowel length and overall duration. Latencies were longer for long-vowel words than for short-vowel words in lexical decision but not in naming. Further, lexical decision on long-vowel words benefited more from identity priming than lexical decision on short-vowel words, suggesting that representations of long-vowel words achieve activation thresholds more slowly. The discussion focused on phonetically informed phonologies, particularly gestural phonology and its potential for understanding reading acquisition and performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of kanji and kana reading on cerebral blood flow patterns measured by PET

To investigate the respective functions of pathways in processing visual information from different types of symbols, by positron emission tomography (PET) we examined the effect on cerebral blood flow (CBF) of reading the Japanese morphogram (kanji) versus the syllabogram (kana). Nine Japanese men were presented with three visual conditions in random order 2 minutes before the scan: eyes open controls, kanji morphogram reading, and kana syllabogram reading. Three words written in kanji or kana were shown, and subjects were instructed to read them silently and to identify the word unrelated logically to the other two. The reading and analyzing tasks activated wide areas of vision-related cortices. The comparison of the kanji and kana readings showed higher metabolism, with the former only in the posterior part of the primary visual cortex. Most of the CBF increases were common for both stimuli, although the patterns of these increases differed slightly. The correlation matrix of CBF change in the left hemisphere showed a ventral connection in kanji reading and a dorsal connection in kana reading. Our results suggest there is a functional differentiation in the brain between patterned and sequential perception when reading Japanese morphograms and syllabograms.     

Prefrontal and parietal regions are involved in naming of objects seen from unusual viewpoints.

Object naming is commonly used for demonstrating semantic memory abilities, known to be affected in normal aging. Yet, neuropsychological assessments of older people do not reflect irregularities. The authors used a test with 2 levels of naming complexity by 2 kinds of stimuli: common objects pictured from a conventional viewpoint (usual condition) or from an unconventional viewpoint (unusual condition). The authors studied naming performance with 129 healthy participants, aged 20-85 years. For the usual stimuli, the success rate was high (90.9%), with no reduction in performance until 65 years of age. However, for the unusual stimuli, there was a marked reduction in performance with age. Brain activity was studied on 11 healthy young participants (20-30 years of age) using functional magnetic resonance imaging. The usual condition activated brain regions associated with visual perception, language, and memory. Additional brain regions associated with semantic searching and decision making were obtained in the unusual condition in the prefrontal cortex (Brodmann's area [BA] 9 and BA 47) and anterior cingulate (BA 32). The results suggest that the poor naming performance for unusual-viewed objects in older people might be related to the shrinkage of frontal gray matter with age. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Contribution of human hippocampal region to novelty detection

The ability to respond to unexpected stimuli (the 'orienting response') is a fundamental characteristic of mammalian behaviour, but the brain mechanisms by which novelty is detected remain poorly defined. Electrophysiological recordings of scalp and intracranial event-related potentials (ERPs) have shown that novel stimuli activate a distributed network involving prefrontal and posterior association cortex. In addition, ERP and single-neuron recordings, as well as neuroimaging and modelling studies, have suggested that temporal cortical regions, including the hippocampus, are also involved. To examine further the role of the medial temporal lobe in novelty processing, I measured physiological responses to novel auditory and tactile stimuli in patients with damage to the posterior hippocampal region. In normal control subjects, unexpected novel stimuli produce a characteristic ERP signal, accompanied by an autonomic skin response. Both responses are reduced in hippocampal lesion patients, whereas the response to expected control stimuli is unaffected. Thus the hippocampal region, in addition to its known role in memory formation, is an essential component of the distributed limbic-cortical network that detects and responds to novel stimuli.     

Analysis of neural interactions explains the activation of occipital cortex by an auditory stimulus

Analysis of neural interactions explains the activation of occipital cortex by an auditory stimulus. J. Neurophysiol. 80: 2790-2796, 1998. Large-scale neural interactions were characterized in human subjects as they learned that an auditory stimulus signaled a visual event. Once learned, activation of left dorsal occipital cortex (increased regional cerebral blood flow) was observed when the auditory stimulus was presented alone. Partial least-squares analysis of the interregional correlations (functional connectivity) between the occipital area and the rest of the brain identified a pattern of covariation with four dominant brain areas that could have mediated this activation: prefrontal cortex (near Brodmann area 10, A10), premotor cortex (A6), superior temporal cortex (A41/42), and contralateral occipital cortex (A18). Interactions among these regions and the occipital area were quantified with structural equation modeling to identify the strongest sources of the effect on left occipital activity (effective connectivity). Learning-related changes in feedback effects from A10 and A41/42 appeared to account for this change in occipital activity. Influences from these areas on the occipital area were initially suppressive, or negative, becoming facilitory, or positive, as the association between the auditory and visual stimuli was acquired. Evaluating the total effects within the functional models showed positive influences throughout the network, suggesting enhanced interactions may have primed the system for the now-expected visual discrimination. By characterizing both changes in activity and the interactions underlying sensory associative learning, we demonstrated how parts of the nervous system operate as a cohesive network in learning about and responding to the environment.     

Brain potentials associated with perceptual priming vs explicit remembering during the repetition of visual word-form

Priming of visual word-form was studied using a reading manipulation in which some words appeared in a backward format (e.g., d-r-o-w) instead of the usual forward format. In Experiment 1, subjects discriminated occasional targets (common first names) from other words with a speeded response. Reaction time was faster for words that had also appeared earlier in the forward format compared to the backward format. Event-related potentials (ERPs) recorded in response to word presentations showed a corresponding difference, a positive offset present during the time interval beginning about 300 ms after word onset from electrodes over occipital and parietal cortex. In Experiment 2, the task was changed to a recognition test, and a later and more widespread ERP response was observed, thus confirming the association between the ERP difference in Experiment 1 and priming rather than explicit remembering. ERP measures were presumably sensitive to neural events underlying the specific influence of recent reading experiences on the processing of visual word-form, thus providing real-time evidence on the neural mechanisms of priming.     

Modelling of intraperitoneal chemohyperthermia: experimental study and identification of certain thermal aspects

The purpose of this study was to examine regional cerebral blood flow using positron emission tomography (PET) during the performance of tasks related to visual confrontation naming. Ten healthy, young participants were scanned twice in each of 5 conditions; blood flow was measured using standard PET [15O]-water technology. Two major findings have replicated previous studies. First, the naming of visually presented objects, whether covert or overt, requires a region of the left inferior cortex including the fusiform gyrus. Second, during overt naming, there is an increase in activity in the inferior or frontal cortex and insula as a consequence of generating speech code. These data are consistent with other studies demonstrating the importance of the inferior temporal regions for semantic processing, and the frontal cortex for word form generation.     

The temporal dynamics of reading: a PET study

The temporal dynamics of evoked brain responses are normally characterized using electrophysiological techniques but the positron emission tomography study presented here revealed a temporal aspect of reading by correlating the duration a word remained in the visual field with evoked haemodynamic response. Three distinct types of effects were observed: in visual processing areas, there were linear increases in activity with duration suggesting that visual processing endures throughout the time the stimulus remains in the visual field. In right hemisphere areas, there were monotonic decreases in activity with increased duration which we relate to decreased attention for longer stimulus durations. In left hemisphere word processing areas there were inverted U-shaped dependencies between activity and word duration indicating that, after 400-600 ms, activity in word processing areas is progressively reduced if the word remains in the visual field. We conclude that these inverted U effects in left hemisphere language areas reflect the temporal dynamics of visual word processing and we highlight the implication of these effects for the design of activation studies involving reading.     

Functional MRI activation in children with and without dyslexia during pseudoword aural repeat and visual decode: Before and after treatment.

Children without dyslexia (n=10) received nonphonological treatment, and those with dyslexia received phonological (n=11) or nonphonological (n=9) treatment. Before and after treatment they performed aural repeat, visual decode, and aural match pseudoword tasks during functional MRI scanning that separated stimulus input from response production. Group map analysis indicated that children with dyslexia overactivated compared with good readers during the aural-repeat/aural-match contrast in bilateral frontal (Brodmann's area [BA] 3, 4, 5, 6, 9), left parietal (BA 2, 3), left temporal (BA 38), and right temporal (BA 20, 21, 37) regions (stimulus input) and underactivated in right frontal (BA 24, 32) and right insula (BA 48) regions (response production); they underactivated in BA 19/V5 during the visual-decode/aural-match contrast (response production). Individual brain analysis for children with dyslexia revealed that during the aural-repeat/aural-match contrast (stimulus input), phonological treatment decreased and normalized activation in left supramarginal gyrus and postcentral gyrus. Nonphonological treatment increased and normalized activation during the visual-decode/aural-match contrast (response production) in BA19/V5 and changed activation in the same direction as good readers during aural-repeat/aural-match contrast (stimulus input) in left postcentral gyrus. The significance of the findings for competing theories of dyslexia is discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Functional mapping of human memory using PET: Comparisons of conceptual and perceptual tasks.

Tested whether different neurological regions subserved the conceptual and perceptual memory components by using positron emission tomography (PET). Regional cerebral blood flow (RCBF) of 14 Ss (mean age 25 yrs) during 2 conceptual tasks of semantic cued recall and semantic association was compared to a control condition in which Ss made semantic associations to nonstudied words. RCBF during 2 perceptual tasks of word fragment cued recall and word fragment completion was also compared to a word fragment nonstudied control condition. There were clear dissociations in RCBF that reflected differences in brain regions subserving the 2 types of memory processes. Conceptual processing produced more activation in the left frontal and temporal cortex and the lateral aspect of the bilateral inferior parietal lobule. Perceptual memory processing activated the right frontal and temporal cortex and the bilateral posterior areas. (French abstract) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rat testicular extracellular superoxide dismutase: its purification, cellular distribution, and regulation

Rehabilitative measures for stroke are not generally based on basic neurobiological principles, despite evidence from animal models that certain anatomical and pharmacological changes correlate with recovery. In this report, we use functional magnetic resonance imaging (fMRI) to study in vivo human brain reorganization in a right handed patient with an acquired reading disorder from stroke. With phonological dyslexia, her whole-word (lexical) reading approach included inability to read nonwords and poor reading of function words. Following therapy, she was able to read nonwords and function words, and preferred a decompositional (sub-lexical) strategy in general. fMRI was performed during a reading task before and after treatment. Prior to therapy, her main focus of brain activation was in the left angular gyrus (area 39). After therapy, it was instead in the left lingual gyrus (area 18). This result suggests first that it is possible to alter brain physiology with therapy for acquired language disorders, and second, that two reading strategies commonly used in normal reading use distinct neural circuits, possibly reconciling several conflicting neuroimaging studies of reading.     

Theoretical analysis of the cognitive processing of lexical and pictorial stimuli: Reading, naming, and visual and conceptual comparisons.

This article reviews the research literature on the differences between word reading and picture naming. A theory for the visual and cognitive processing of pictures and words is then introduced. The theory accounts for slower naming of pictures than reading of words. Reading aloud involves a fast, grapheme-to-phoneme transformation process, whereas picture naming involves two additional processes; (a) determining the meaning of the pictorial stimulus and (b) finding a name for the pictorial stimulus. We conducted a reading-naming experiment, and the time to achieve (a) and (b) was determined to be approximately 160 ms. On the basis of data from a second experiment, we demonstrated that there is no significant difference in time to visually compare two pictures or two words when size of the stimuli is equated. There is no difference in time to make the two types of cross-modality conceptual comparisons (picture first, then word, or word first, then picture). The symmetry of the visual and conceptual comparison results supports the hypothesis that the coding of the mind is neither intrinsically linguistic nor imagistic, but rather it is abstract. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prediction of children's reading skills using behavioral, functional, and structural neuroimaging measures.

The ability to decode letters into language sounds is essential for reading success, and accurate identification of children at high risk for decoding impairment is critical for reducing the frequency and severity of reading impairment. We examined the utility of behavioral (standardized tests), and functional and structural neuroimaging measures taken with children at the beginning of a school year for predicting their decoding ability at the end of that school year. Specific patterns of brain activation during phonological processing and morphology, as revealed by voxel-based morphometry (VBM) of gray and white matter densities, predicted later decoding ability. Further, a model combining behavioral and neuroimaging measures predicted decoding outcome significantly better than either behavioral or neuroimaging models alone. Results were validated using cross-validation methods. These findings suggest that neuroimaging methods may be useful in enhancing the early identification of children at risk for poor decoding and reading skills. (PsycINFO Database Record (c) 2010 APA, all rights reserved)