Reading the mind's eye: online detection of visuo-spatial working memory and visual imagery in the inferior temporal lobe

Several brain regions involved in visual perception have been shown to also participate in non-sensory cognitive processes of visual representations. Here we studied the role of ventral visual pathway areas in visual imagery and working memory. We analyzed intracerebral EEG recordings from the left inferior temporal lobe of an epileptic patient during working memory tasks and mental imagery. We found that high frequency gamma-band activity (50-150 Hz) in the inferior temporal gyrus (ITG) increased with memory load only during visuo-spatial, but not verbal, working memory. Using a real-time set-up to measure and visualize gamma-band activity online - BrainTV - we found a systematic activity increase in ITG when the patient was visualizing a letter (visual imagery), but not during perception of letters. In contrast, only 7 mm more medially, neurons located in the fusiform gyrus exhibited a complete opposite pattern, responding during verbal working memory retention and letter presentation, but not during imagery or visuo-spatial working memory maintenance. Talairach coordinates indicate that the fusiform contact site corresponds to the word form area, suggesting that this region has a role not only in processing letter-strings, but also in working memory retention of verbal information. We conclude that neural networks supporting imagination of a visual element are not necessarily the same as those underlying perception of that element. Additionally, we present evidence that gamma-band activity in the inferior temporal lobe, can be used as a direct measure of the efficiency of top-down attentional control over visual areas with implications for the development of novel brain-computer interfaces. Finally, by just reading gamma-band activity in these two recording sites, it is possible to determine, accurately and in real-time, whether a given memory content is verbal or visuo-spatial.     

Dissociation of working memory processing associated with native and second languages: PET investigation

Verbal working memory plays a significant role in language comprehension and problem-solving. The prefrontal cortex has been suggested as a critical area in working memory. Given that domain-specific dissociations of working memory may exist within the prefrontal cortex, it is possible that there may also be further functional divisions within the verbal working memory processing. While differences in the areas of the brain engaged in native and second languages have been demonstrated, little is known about the dissociation of verbal working memory associated with native and second languages. We have used H2(15)O positron emission tomography in 14 normal subjects in order to identify the neural correlates selectively involved in working memory of native (Korean) and second (English) languages. All subjects were highly proficient in the native language but poorly proficient in the second language. Cognitive tasks were a two-back task for three kinds of visually presented objects: simple pictures, English words, and Korean words. The anterior portion of the right dorsolateral prefrontal cortex and the left superior temporal gyrus were activated in working memory for the native language, whereas the posterior portion of the right dorsolateral prefrontal cortex and the left inferior temporal gyrus were activated in working memory for the second language. The results suggest that the right dorsolateral prefrontal cortex and left temporal lobe may be organized into two discrete, language-related functional systems. Internal phonological processing seems to play a predominant role in working memory processing for the native language with a high proficiency, whereas visual higher order control does so for the second language with a low proficiency.     

Parahippocampal Activation during Successful Recognition of Words: A Self-Paced Event-Related fMRI Study

In this study, we investigated retrieval from verbal episodic memory using a self-paced event-related fMRI paradigm, similar to the designs typically used in behavioral studies of memory function. We tested the hypothesis that the medial temporal lobe (MTL) is involved in the actual recovery of verbal information (retrieval success) rather than in the attempt to retrieve information (retrieval attempt). To this end, we used a verbal recognition task, distinguishing correctly recognized words, correctly rejected words, and a low-level baseline condition. Directly contrasting correct recognition with correct rejection of words, we found activation in the left fusiform/parahippocampal gyrus, indicating that this region has a distinct role in the successful retrieval of verbal information. Furthermore, our results were in agreement with those of previous imaging studies that compared a fixed-paced verbal recognition task to a baseline condition, showing activation in bilateral inferior frontal cortex, left dorsolateral prefrontal cortex, left anterior insular cortex, and anterior cingulate. This demonstrates the applicability of a self-paced event-related design within imaging studies of memory function.     

The irrelevant speech effect and working memory load

Irrelevant speech impairs the immediate serial recall of visually presented material. Previously, we have shown that the irrelevant speech effect (ISE) was associated with a relative decrease of regional blood flow in cortical regions subserving the verbal working memory, in particular the superior temporal cortex. In this extension of the previous study, the working memory load was increased and an increased activity as a response to irrelevant speech was noted in the dorsolateral prefrontal cortex. We suggest that the two studies together provide some basic insights as to the nature of the irrelevant speech effect. Firstly, no area in the brain can be ascribed as the single locus of the irrelevant speech effect. Instead, the functional neuroanatomical substrate to the effect can be characterized in terms of changes in networks of functionally interrelated areas. Secondly, the areas that are sensitive to the irrelevant speech effect are also generically activated by the verbal working memory task itself. Finally, the impact of irrelevant speech and related brain activity depends on working memory load as indicated by the differences between the present and the previous study. From a brain perspective, the irrelevant speech effect may represent a complex phenomenon that is a composite of several underlying mechanisms, which depending on the working memory load, include top-down inhibition as well as recruitment of compensatory support and control processes. We suggest that, in the low-load condition, a selection process by an inhibitory top-down modulation is sufficient, whereas in the high-load condition, at or above working memory span, auxiliary adaptive cognitive resources are recruited as compensation.     

Occipito-parietal cortex activation during visuo-spatial imagery in early blind humans

Using positron emission tomography, regional cerebral blood flow was studied in five early blind and five control volunteers during visuo-spatial imagery. Subjects were instructed to generate a mental representation of verbally provided bidimensional patterns that were placed in a grid and to assess pattern symmetry in relation to a grid axis. This condition was contrasted with a verbal memory task. Cerebral activation in both groups was similar during the visuo-spatial imagery task. It involved the precuneus (BA 7), superior parietal lobule (BA 7), and occipital gyrus (BA 19). These results are in accordance with previous studies conducted in sighted subjects that indicated that the same occipito-parietal areas are involved in visual perception as well as in mental imagery dealing with spatial components. The dorsal pathway seems to be involved in visuo-spatial imagery in early blind subjects, indicating that this pathway undergoes development in the absence of vision.     

Left TPJ activity in verbal working memory: implications for storage- and sensory-specific models of short term memory

Patients with damage to the left temporoparietal junction (TPJ) have a low verbal span without concomitant deficits in speech perception. This pattern of cognitive impairment is taken as evidence for a dedicated phonological buffer that plays little role in perception (storage-specific account). In contrast, other research suggests that items are maintained and perceived in the same regions (sensory-specific account). In an fMRI study, we demonstrate that the left TPJ does not respond in a way predicted of a phonological buffer; that is, activity in this region is not sustained during encoding or maintenance. Instead, a region in the superior temporal gyrus that has been associated with both speech perception and production demonstrated the expected profile of a store: it was more active in the verbal condition than the object condition and was active during both encoding and maintenance. These results support the sensory-specific account of short term memory rather than the storage-specific account. Based on the pattern of activity in the left TPJ, we suggest that the impairment of verbal working memory observed in patients with TPJ damage may be due to diminished attentional processes rather than reduced storage capacity.     

Neural correlates of simple and complex mental calculation

Some authors proposed that exact mental calculation is based on linguistic representations and relies on the perisylvian language cortices, while the understanding of proximity relations between numerical quantities implicates the parietal cortex. However, other authors opposed developmental arguments to suggest that number sense emerges from nonspecific visuospatial processing areas in the parietal cortex. Within this debate, the present study aimed at revealing the functional anatomy of the two basic resolution strategies involved in mental calculation, namely arithmetical fact retrieval and actual computation, questioning in particular the respective role of language and/or visuospatial cerebral areas. Regional cerebral blood flow was measured with positron emission tomography while subjects were at rest (Rest), read digits (Read), retrieved simple arithmetic facts from memory (i.e., 2 x 4, Retrieve), and performed mental complex calculation (i.e., 32 x 24, Compute). Compared to Read, Retrieve engaged a left parieto-premotor circuit representing a developmental trace of a finger-counting representation that mediates, by extension, the numerical knowledge in adult. Beside this basic network, Retrieve involved a naming network, including the left anterior insula and the right cerebellar cortex, while it did not engage the perisylvian language areas, which were deactivated as compared to Rest. In addition to this retrieval network, Compute specifically involved two functional networks: a left parieto-frontal network in charge of the holding of the multidigit numbers in visuospatial working memory and a bilateral inferior temporal gyri related to the visual mental imagery resolution strategy. Overall, these results provide strong evidence of the involvement of visuospatial representations in different levels of mental calculation.     

Interaction between a verbal working memory network and the medial temporal lobe

The irrelevant speech effect illustrates that sounds that are irrelevant to a visually presented short-term memory task still interfere with neuronal function. In the present study we explore the functional and effective connectivity of such interference. The functional connectivity analysis suggested an interaction between the level of irrelevant speech and the correlation between in particular the left superior temporal region, associated with verbal working memory, and the left medial temporal lobe. Based on this psycho-physiological interaction, and to broaden the understanding of this result, we performed a network analysis, using a simple network model for verbal working memory, to analyze its interaction with the medial temporal lobe memory system. The results showed dissociations in terms of network interactions between frontal as well as parietal and temporal areas in relation to the medial temporal lobe. The results of the present study suggest that a transition from phonological loop processing towards an engagement of episodic processing might take place during the processing of interfering irrelevant sounds. We speculate that, in response to the irrelevant sounds, this reflects a dynamic shift in processing as suggested by a closer interaction between a verbal working memory system and the medial temporal lobe memory system.     

Age-related changes in working memory during sentence comprehension: an fMRI study.

Sentence comprehension declines with age, but the neural basis for this change is unclear. We monitored regional brain activity in 13 younger subjects and 11 healthy seniors matched for sentence comprehension accuracy while they answered a simple probe about written sentences. The sentences varied in their grammatical features (subject-relative vs object-relative subordinate clause) and their verbal working memory (WM) demands (short vs long antecedent noun-gap linkage). We found that young and senior subjects both recruit a core written sentence processing network, including left posterolateral temporal and bilateral occipital cortex for all sentences, and ventral portions of left inferior frontal cortex for object-relative sentences with a long noun-gap linkage. Differences in activation patterns for seniors compared to younger subjects were due largely to changes in brain regions associated with a verbal WM network. While seniors had less left parietal recruitment than younger subjects, left premotor cortex, and dorsal portions of left inferior frontal cortex showed greater activation in seniors compared to younger subjects. Younger subjects recruited right posterolateral temporal cortex for sentences with a long noun-gap linkage. Seniors additionally recruited right parietal cortex for this sentence-specific form of WM. Our findings are consistent with the hypothesis that the neural basis for sentence comprehension includes dissociable but interactive large-scale neural networks supporting core written sentence processes and related cognitive resources involved in WM. Seniors with good comprehension appear to up-regulate portions of the neural substrate for WM during sentence processing to achieve comprehension accuracy that equals young subjects.     

Enhanced early-latency electromagnetic activity in the left premotor cortex is associated with successful phonetic categorization

Sensory-motor interactions between auditory and articulatory representations in the dorsal auditory processing stream are suggested to contribute to speech perception, especially when bottom-up information alone is insufficient for purely auditory perceptual mechanisms to succeed. Here, we hypothesized that the dorsal stream responds more vigorously to auditory syllables when one is engaged in a phonetic identification/repetition task subsequent to perception compared to passive listening, and that this effect is further augmented when the syllables are embedded in noise. To this end, we recorded magnetoencephalography while twenty subjects listened to speech syllables, with and without noise masking, in four conditions: passive perception; overt repetition; covert repetition; and overt imitation. Compared to passive listening, left-hemispheric N100m equivalent current dipole responses were amplified and shifted posteriorly when perception was followed by covert repetition task. Cortically constrained minimum-norm estimates showed amplified left supramarginal and angylar gyri responses in the covert repetition condition at ~100ms from stimulus onset. Longer-latency responses at ~200ms were amplified in the covert repetition condition in the left angular gyrus and in all three active conditions in the left premotor cortex, with further enhancements when the syllables were embedded in noise. Phonetic categorization accuracy and magnitude of voice pitch change between overt repetition and imitation conditions correlated with left premotor cortex responses at ~100 and ~200ms, respectively. Together, these results suggest that the dorsal stream involvement in speech perception is dependent on perceptual task demands and that phonetic categorization performance is influenced by the left premotor cortex.     

Imagery of a moving object: The role of occipital cortex and human MT/V5+

Visual imagery – similar to visual perception – activates feature-specific and category-specific visual areas. This is frequently observed in experiments where the instruction is to imagine stimuli that have been shown immediately before the imagery task. Hence, feature-specific activation could be related to the short-term memory retrieval of previously presented sensory information.Here, we investigated mental imagery of stimuli that subjects had not seen before, eliminating the effects of short-term memory. We recorded brain activation using fMRI while subjects performed a behaviourally controlled guided imagery task in predefined retinotopic coordinates to optimize sensitivity in early visual areas.Whole brain analyses revealed activation in a parieto-frontal network and lateral–occipital cortex. Region of interest (ROI) based analyses showed activation in left hMT/V5+. Granger causality mapping taking left hMT/V5+ as source revealed an imagery-specific directed influence from the left inferior parietal lobule (IPL). Interestingly, we observed a negative BOLD response in V1–3 during imagery, modulated by the retinotopic location of the imagined motion trace.Our results indicate that rule-based motion imagery can activate higher-order visual areas involved in motion perception, with a role for top-down directed influences originating in IPL. Lower-order visual areas (V1, V2 and V3) were down-regulated during this type of imagery, possibly reflecting inhibition to avoid visual input from interfering with the imagery construction. This suggests that the activation in early visual areas observed in previous studies might be related to short- or long-term memory retrieval of specific sensory experiences.     

Selective activation of the superior frontal gyrus in task-switching: an event-related fNIRS study

In the task-switching paradigm, reaction time is longer and accuracy is worse in switch trials relative to repetition trials. This so-called switch cost has been ascribed to the engagement of control processes required to alternate between distinct stimulus-response mapping rules. Neuroimaging studies have reported an enhanced activation of the human lateral prefrontal cortex and the superior frontal gyrus during the task-switching paradigm. Whether neural activation in these regions is dissociable and associated with separable cognitive components of task switching has been a matter of recent debate. We used multi-channel near-infrared spectroscopy (fNIRS) to measure brain cortical activity in a task-switching paradigm designed to avoid task differences, order predictability, and frequency effects. The results showed a generalized bilateral activation of the lateral prefrontal cortex and the superior frontal gyrus in both switch trials and repetition trials. To isolate the activity selectively associated with the task-switch, the overall activity recorded during repetition trials was subtracted from the activity recorded during switch trials. Following subtraction, the remaining activity was entirely confined to the left portion of the superior frontal gyrus. The present results suggest that factors associated with load and maintenance of distinct stimulus-response mapping rules in working memory are likely contributors to the activation of the lateral prefrontal cortex, whereas only activity in the left superior frontal gyrus can be linked unequivocally to switching between distinct cognitive tasks.     

Overlapping neural regions for processing rapid temporal cues in speech and nonspeech signals

Speech perception involves recovering the phonetic form of speech from a dynamic auditory signal containing both time-varying and steady-state cues. We examined the roles of inferior frontal and superior temporal cortex in processing these aspects of auditory speech and nonspeech signals. Event-related functional magnetic resonance imaging was used to record activation in superior temporal gyrus (STG) and inferior frontal gyrus (IFG) while participants discriminated pairs of either speech syllables or nonspeech tones. Speech stimuli differed in either the consonant or the vowel portion of the syllable, whereas the nonspeech signals consisted of sinewave tones differing along either a dynamic or a spectral dimension. Analyses failed to identify regions of activation that clearly contrasted the speech and nonspeech conditions. However, we did identify regions in the posterior portion of left and right STG and left IFG yielding greater activation for both speech and nonspeech conditions that involved rapid temporal discrimination, compared to speech and nonspeech conditions involving spectral discrimination. The results suggest that, when semantic and lexical factors are adequately ruled out, there is significant overlap in the brain regions involved in processing the rapid temporal characteristics of both speech and nonspeech signals.     

Comprehension of degraded speech sounds with m-sequence modulation: An fMRI study

In a recent electroencephalography (EEG) study (Takeichi et al., 2007a), we developed a new technique for assessing speech comprehension using speech degraded by m-sequence modulation and found a correlation peak with a 400-ms delay. This peak depended on the comprehensibility of the modulated speech sounds. Here we report the results of a functional magnetic resonance imaging (fMRI) experiment comparable to our previous EEG experiment. We examined brain areas related to verbal comprehension of the modulated speech sound to examine which neural system processes this modulated speech. A non-integer, alternating-block factorial design was used with 23 Japanese-speaking participants, with time reversal and m-sequence modulation as factors. A main effect of time reversal was found in the left temporal cortex along the superior temporal sulcus (BA21 and BA39), left precentral gyrus (BA6) and right inferior temporal gyrus (BA21). A main effect of modulation was found in the left postcentral gyrus (BA43) and the right medial frontal gyri (BA6) as an increase by modulation and in the left temporal cortex (BA21, 39), parahippocampal gyrus (BA34), posterior cingulate (BA23), caudate and thalamus and right superior temporal gyrus (BA38) as a decrease by modulation. An interaction effect associated specifically with non-modulated speech was found in the left frontal gyrus (BA47), left occipital cortex in the cuneus (BA18), left precuneus (BA7, 31), right precuneus (BA31) and right thalamus (forward > reverse). The other interaction effect associated specifically with modulation of speech sound was found in the inferior frontal gyrus in the opercular area (BA44) (forward > reverse). Estimated scalp projection of the component correlation function (Cao et al., 2002) for the corresponding EEG data (Takeichi et al., 2007a, showed leftward dominance. Hence, activities in the superior temporal sulcus (BA21 and BA39), which are commonly observed for speech processing, as well as left precentral gyrus (BA6) and left inferior frontal gyrus in the opercular area (BA44) is suggested to contribute to the comprehension-related EEG signal.     

Verbal storage in a premotor-parietal network: evidence from fMRI-guided magnetic stimulation

Phonological rehearsal helps to keep selected information consciously in mind for further processing. This part of short-term storage takes place during the delay period of verbal working memory tasks and involves a frontoparietal network as functional magnetic resonance imaging (fMRI) studies have shown. The involved cortical areas can be further investigated by interfering with the local information processing using transcranial magnetic stimulation (TMS). On a single subject level, we identified predominantly left-sided premotor, prefrontal, and parietal areas active during the delay period of a verbal working memory task using event-related fMRI. In a pilot approach, TMS was neuronavigated to the individually active areas by using a stereotaxic device. Then, TMS was applied during the delay period of similar tasks as in fMRI. Error rates increased significantly upon stimulating left premotor cortex, but not upon parietal or prefrontal stimulation. The contribution of the premotor cortex to storage and rehearsal is discussed as an active top-down storage process within the frontoparietal network.     

Prolonged reaction time to a verbal working memory task predicts increased power of posterior parietal cortical activation

We used multislice functional magnetic resonance imaging (fMRI) to investigate the association between behavioral and neurophysiological measures of working memory task performance in 20 right-handed male healthy volunteers. Images were acquired over a 5-min period at 1.5 Tesla. We used a periodic design, alternating 30-s blocks of the "n-back" working memory task with 30-s blocks of a sensorimotor control task to activate verbal working memory systems. The power of functional response to the task was estimated by sinusoidal regression at each voxel. The relationship between power of fMRI response and mean reaction time over all 11 working memory trials was explored by multiple regression, with age and mean reaction time to the control task as covariates, at voxel and regional levels of analysis. All subjects were able to perform the n-back task accurately. A spatially distributed network was activated, including dorsolateral prefrontal cortex, inferior frontal gyrus, lateral premotor cortex, and supplementary motor area (SMA) in the frontal lobes. More posteriorly, there were major foci of activation in parietal and occipitoparietal cortex, precuneus, lingual, and fusiform gyri of the ventral occipital lobe, inferior temporal gyrus, and cerebellum. The power of functional response was positively correlated with reaction time in bilateral posterior parietal cortex (Talairach coordinates in x, y, z (mm) 35, -44, 37 and -32, -56, 42), indicating that subjects who found the task difficult, and responded with a slower reaction time, tended to activate these regions more powerfully. One interpretation of this regionally specific relationship between prolonged reaction time and increased power of posterior parietal activation is consistent with prior studies identifying similar areas of parietal cortex as the site of the phonological storage function in verbal working memory.     

The synchronization of the human cortical working memory network

A verbal reasoning problem at the intersection of verbal working memory, problem-solving, and language comprehension was examined using event-related fMRI to distinguish differences in the differential timing of the response of the various cortical regions that compose the working memory network. Problems were developed such that the process demand as well as the timing of the manipulation of the contents of working memory (i.e., a demanding computation) was varied. Activation was observed in several regions including the dorsolateral prefrontal cortex, the inferior frontal gyrus, and the parietal lobe. Examination of the MR amplitude response revealed that the regions do not all activate simultaneously; instead, their activation time courses reveal differential responses that correspond to their theoretical processing role in the problem-solving task. The coordination of cortical area responses reveals how the various cortical regions synchronize and collaborate in order to accomplish a given cognitive function.     

Neural correlates of artificial grammar learning

Artificial grammar learning (AGL) is a form of nondeclarative memory that involves the nonconscious acquisition of abstract rules. While data from amnesic patients indicate that AGL does not depend on the medial temporal lobe, the neural basis of this type of memory is unknown and was therefore examined using event-related fMRI. Prior to scanning, participants studied letter strings constructed according to an artificial grammar. Participants then made grammaticality judgments about novel grammatical and nongrammatical strings while fMRI data were collected. The participants successfully acquired knowledge of the grammar, as evidenced by correct identification of the grammatical letter strings (57.4% correct; SE 1.9). During grammaticality judgments, widespread increases in activity were observed throughout the occipital, posterior temporal, parietal, and prefrontal cortical areas, reflecting the cognitive demands of the task. More specific analyses contrasting grammatical and nongrammatical strings identified greater activity in left superior occipital cortex and the right fusiform gyrus for grammatical stimuli. Increased activity was also observed in the left superior occipital and left angular gyrus for correct responses compared to incorrect. Comparing activity during grammaticality judgments versus a matched recognition control task again identified greater activation in the left angular gyrus. The network of areas exhibiting increased activity for grammatical stimuli appears to have more in common with studies examining word-form processing or mental calculation than the fluency effects previously reported for nondeclarative memory tasks such as priming and visual categorization. These results suggest that a novel nondeclarative memory mechanism supporting AGL exists in the left superior occipital and inferior parietal cortex.     

Neural mechanisms of auditory awareness underlying verbal transformations

Prolonged listening to a repeated word without a pause produces a series of illusory transitions of the physically unchanging word, which is called verbal transformation. Verbal transformations provide a rare opportunity to examine how auditory percepts are formed in the brain. We found that verbal forms are affected by phonetic reorganization of a word, rather than by auditory adaptation and lexical distortion of it. We identified brain activity leading to individual differences between perceptual transitions and tone detection. An event-related fMRI analysis revealed that the left inferior frontal cortex (IFC), anterior cingulate cortex (ACC), and the left prefrontal cortex were activated when perceptual transitions from one verbal form to another occurred, but not when tone pips were detected. The number of perceptual transitions showed positive and negative correlations with signal intensity in the left IFC and the left ACC, respectively. The results suggest that active generation of verbal forms is linked with articulatory gestures for speech production and that the frequency of perceptual transitions is determined by a balance of the activations between the two brain regions. Structural equation modeling demonstrated that individual differences in the number of perceptual transitions rely on negative feedback from the ACC to the IFC via the posterior insula. These findings suggest that distributed frontal areas are involved in auditory awareness underlying verbal transformations.     

Song and speech: brain regions involved with perception and covert production

This 3-T fMRI study investigates brain regions similarly and differentially involved with listening and covert production of singing relative to speech. Given the greater use of auditory-motor self-monitoring and imagery with respect to consonance in singing, brain regions involved with these processes are predicted to be differentially active for singing more than for speech. The stimuli consisted of six Japanese songs. A block design was employed in which the tasks for the subject were to listen passively to singing of the song lyrics, passively listen to speaking of the song lyrics, covertly sing the song lyrics visually presented, covertly speak the song lyrics visually presented, and to rest. The conjunction of passive listening and covert production tasks used in this study allow for general neural processes underlying both perception and production to be discerned that are not exclusively a result of stimulus induced auditory processing nor to low level articulatory motor control. Brain regions involved with both perception and production for singing as well as speech were found to include the left planum temporale/superior temporal parietal region, as well as left and right premotor cortex, lateral aspect of the VI lobule of posterior cerebellum, anterior superior temporal gyrus, and planum polare. Greater activity for the singing over the speech condition for both the listening and covert production tasks was found in the right planum temporale. Greater activity in brain regions involved with consonance, orbitofrontal cortex (listening task), subcallosal cingulate (covert production task) were also present for singing over speech. The results are consistent with the PT mediating representational transformation across auditory and motor domains in response to consonance for singing over that of speech. Hemispheric laterality was assessed by paired t tests between active voxels in the contrast of interest relative to the left-right flipped contrast of interest calculated from images normalized to the left-right reflected template. Consistent with some hypotheses regarding hemispheric specialization, a pattern of differential laterality for speech over singing (both covert production and listening tasks) occurs in the left temporal lobe, whereas, singing over speech (listening task only) occurs in right temporal lobe.