Broca's area and the discrimination of frequency transitions: a functional MRI study

Fate of the second task in dual-task interference is associated with sensory system interactions with default-mode network

Psychological refractory period (PRP) effect refers to the delay in responding to the second of two tasks occurring in rapid succession. While all the major models of PRP highlight the importance of the frontoparietal control network (FPCN) in prioritizing the neural processing of the first task, the fate of the second task remains poorly understood. Here, we provide novel neural evidence on how the functional connectivity between sensory systems and the default-mode network (DMN) suspends the neural processing of the second task to ensure the efficient completion of the first task in dual-task situation. In a cross-modal PRP paradigm, a visual task could either precede or follow an auditory task. The DMN was generally deactivated during task performance and selectively coupled with the sensory system underlying the second task subjected to the PRP effect. Specifically, the DMN showed neural coupling with the auditory system when the auditory task came after the visual task, and with the visual system vice versa. More critically, the strength of the DMN-Sensory coupling correlated negatively with the size of the PRP effect: the stronger the coupling, the shorter the PRP. Therefore, rather than being detrimental to the dual-task performance, temporary suspension of the second task, via the DMN-Sensory coupling, surprisingly guaranteed the efficient completion of the first task by reducing the interference from the second task. Accordingly, the entry and processing of the second stimuli in the central executive system were speeded up as well.

Involuntary Orienting and Conflict Resolution during Auditory Attention: The Role of Ventral and Dorsal Streams

Selective attention to sound object features such as pitch and location is associated with enhanced brain activity in ventral and dorsal streams, respectively. We examined the role of these pathways in involuntary orienting and conflict resolution using fMRI. Participants were presented with two tones that may, or may not, share the same nonspatial (frequency) or spatial (location) auditory features. In separate blocks of trials, participants were asked to attend to sound frequency or sound location and ignore the change in the task-irrelevant feature. In both attend-frequency and attend-location tasks, RTs were slower when the task-irrelevant feature changed than when it stayed the same (involuntary orienting). This behavioral cost coincided with enhanced activity in the pFC and superior temporal gyrus. Conflict resolution was examined by comparing situations where the change in stimulus features was congruent (both features changed) and incongruent (only one feature changed). Participants were slower and less accurate for incongruent than congruent sound features. This congruency effect was associated with enhanced activity in the pFC and was greater in the right superior temporal gyrus and medial frontal cortex during the attend-location task than during the attend-frequency task. Together, these findings do not support a strict division of "labor" into ventral and dorsal streams but rather suggest interactions between these pathways in situations involving changes in task-irrelevant sound feature and conflict resolution. These findings also validate the Test of Attention in Listening task by revealing distinct neural correlates for involuntary orienting and conflict resolution.

Brain dynamics and connectivity networks under natural auditory stimulation

The analysis of functional magnetic resonance imaging (fMRI) data is challenging when subjects are under exposure to natural sensory stimulation. In this study, a two-stage approach was developed to enable the identification of connectivity networks involved in the processing of information in the brain under natural sensory stimulation. In the first stage, the degree of concordance between the results of inter-subject and intra-subject correlation analyses is assessed statistically. The microstructurally (i.e., cytoarchitectonically) defined brain areas are designated either as concordant in which the results of both correlation analyses are in agreement, or as discordant in which one analysis method shows a higher proportion of supra-threshold voxels than does the other. In the second stage, connectivity networks are identified using the time courses of supra-threshold voxels in brain areas contingent upon the classifications derived in the first stage. In an empirical study, fMRI data were collected from 40 young adults (19 males, average age 22.76 ± 3.25), who underwent auditory stimulation involving sound clips of human voices and animal vocalizations under two operational conditions (i.e., eyes-closed and eyes-open). The operational conditions were designed to assess confounding effects due to auditory instructions or visual perception. The proposed two-stage analysis demonstrated that stress modulation (affective) and language networks in the limbic and cortical structures were respectively engaged during sound stimulation, and presented considerable variability among subjects. The network involved in regulating visuomotor control was sensitive to the eyes-open instruction, and presented only small variations among subjects. A high degree of concordance was observed between the two analyses in the primary auditory cortex which was highly sensitive to the pitch of sound clips. Our results have indicated that brain areas can be identified as concordant or discordant based on the two correlation analyses. This may further facilitate the search for connectivity networks involved in the processing of information under natural sensory stimulation.

Areas activated during naturalistic reading comprehension overlap topological visual, auditory, and somatotomotor maps

Cortical mapping techniques using fMRI have been instrumental in identifying the boundaries of topological (neighbor-preserving) maps in early sensory areas. The presence of topological maps beyond early sensory areas raises the possibility that they might play a significant role in other cognitive systems, and that topological mapping might help to delineate areas involved in higher cognitive processes. In this study, we combine surface-based visual, auditory, and somatomotor mapping methods with a naturalistic reading comprehension task in the same group of subjects to provide a qualitative and quantitative assessment of the cortical overlap between sensory-motor maps in all major sensory modalities, and reading processing regions. Our results suggest that cortical activation during naturalistic reading comprehension overlaps more extensively with topological sensory-motor maps than has been heretofore appreciated. Reading activation in regions adjacent to occipital lobe and inferior parietal lobe almost completely overlaps visual maps, whereas a significant portion of frontal activation for reading in dorsolateral and ventral prefrontal cortex overlaps both visual and auditory maps. Even classical language regions in superior temporal cortex are partially overlapped by topological visual and auditory maps. By contrast, the main overlap with somatomotor maps is restricted to a small region on the anterior bank of the central sulcus near the border between the face and hand representations of M-I. Hum Brain Mapp 37:2784-2810, 2016. © 2016 The Authors Human Brain Mapping Published by Wiley Periodicals, Inc.

Testing the dual-pathway model for auditory processing in human cortex

Analogous to the visual system, auditory information has been proposed to be processed in two largely segregated streams: an anteroventral ("what") pathway mainly subserving sound identification and a posterodorsal ("where") stream mainly subserving sound localization. Despite the popularity of this assumption, the degree of separation of spatial and non-spatial auditory information processing in cortex is still under discussion. In the present study, a statistical approach was implemented to investigate potential behavioral dissociations for spatial and non-spatial auditory processing in stroke patients, and voxel-wise lesion analyses were used to uncover their neural correlates. The results generally provided support for anatomically and functionally segregated auditory networks. However, some degree of anatomo-functional overlap between "what" and "where" aspects of processing was found in the superior pars opercularis of right inferior frontal gyrus (Brodmann area 44), suggesting the potential existence of a shared target area of both auditory streams in this region. Moreover, beyond the typically defined posterodorsal stream (i.e., posterior superior temporal gyrus, inferior parietal lobule, and superior frontal sulcus), occipital lesions were found to be associated with sound localization deficits. These results, indicating anatomically and functionally complex cortical networks for spatial and non-spatial auditory processing, are roughly consistent with the dual-pathway model of auditory processing in its original form, but argue for the need to refine and extend this widely accepted hypothesis.

Auditory connections and functions of prefrontal cortex

The functional auditory system extends from the ears to the frontal lobes with successively more complex functions occurring as one ascends the hierarchy of the nervous system. Several areas of the frontal lobe receive afferents from both early and late auditory processing regions within the temporal lobe. Afferents from the early part of the cortical auditory system, the auditory belt cortex, which are presumed to carry information regarding auditory features of sounds, project to only a few prefrontal regions and are most dense in the ventrolateral prefrontal cortex (VLPFC). In contrast, projections from the parabelt and the rostral superior temporal gyrus (STG) most likely convey more complex information and target a larger, widespread region of the prefrontal cortex. Neuronal responses reflect these anatomical projections as some prefrontal neurons exhibit responses to features in acoustic stimuli, while other neurons display task-related responses. For example, recording studies in non-human primates indicate that VLPFC is responsive to complex sounds including vocalizations and that VLPFC neurons in area 12/47 respond to sounds with similar acoustic morphology. In contrast, neuronal responses during auditory working memory involve a wider region of the prefrontal cortex. In humans, the frontal lobe is involved in auditory detection, discrimination, and working memory. Past research suggests that dorsal and ventral subregions of the prefrontal cortex process different types of information with dorsal cortex processing spatial/visual information and ventral cortex processing non-spatial/auditory information. While this is apparent in the non-human primate and in some neuroimaging studies, most research in humans indicates that specific task conditions, stimuli or previous experience may bias the recruitment of specific prefrontal regions, suggesting a more flexible role for the frontal lobe during auditory cognition.

The effect of brain lesions on sound localization in complex acoustic environments

Localizing sound sources of interest in cluttered acoustic environments--as in the 'cocktail-party' situation--is one of the most demanding challenges to the human auditory system in everyday life. In this study, stroke patients' ability to localize acoustic targets in a single-source and in a multi-source setup in the free sound field were directly compared. Subsequent voxel-based lesion-behaviour mapping analyses were computed to uncover the brain areas associated with a deficit in localization in the presence of multiple distracter sound sources rather than localization of individually presented sound sources. Analyses revealed a fundamental role of the right planum temporale in this task. The results from the left hemisphere were less straightforward, but suggested an involvement of inferior frontal and pre- and postcentral areas. These areas appear to be particularly involved in the spectrotemporal analyses crucial for effective segregation of multiple sound streams from various locations, beyond the currently known network for localization of isolated sound sources in otherwise silent surroundings.

Stimulus-dependent activations and attention-related modulations in the auditory cortex: a meta-analysis of fMRI studies

We meta-analyzed 115 functional magnetic resonance imaging (fMRI) studies reporting auditory-cortex (AC) coordinates for activations related to active and passive processing of pitch and spatial location of non-speech sounds, as well as to the active and passive speech and voice processing. We aimed at revealing any systematic differences between AC surface locations of these activations by statistically analyzing the activation loci using the open-source Matlab toolbox VAMCA (Visualization and Meta-analysis on Cortical Anatomy). AC activations associated with pitch processing (e.g., active or passive listening to tones with a varying vs. fixed pitch) had median loci in the middle superior temporal gyrus (STG), lateral to Heschl's gyrus. However, median loci of activations due to the processing of infrequent pitch changes in a tone stream were centered in the STG or planum temporale (PT), significantly posterior to the median loci for other types of pitch processing. Median loci of attention-related modulations due to focused attention to pitch (e.g., attending selectively to low or high tones delivered in concurrent sequences) were, in turn, centered in the STG or superior temporal sulcus (STS), posterior to median loci for passive pitch processing. Activations due to spatial processing were centered in the posterior STG or PT, significantly posterior to pitch processing loci (processing of infrequent pitch changes excluded). In the right-hemisphere AC, the median locus of spatial attention-related modulations was in the STS, significantly inferior to the median locus for passive spatial processing. Activations associated with speech processing and those associated with voice processing had indistinguishable median loci at the border of mid-STG and mid-STS. Median loci of attention-related modulations due to attention to speech were in the same mid-STG/STS region. Thus, while attention to the pitch or location of non-speech sounds seems to recruit AC areas less involved in passive pitch or location processing, focused attention to speech predominantly enhances activations in regions that already respond to human vocalizations during passive listening. This suggests that distinct attention mechanisms might be engaged by attention to speech and attention to more elemental auditory features such as tone pitch or location. This article is part of a Special Issue entitled Human Auditory Neuroimaging.

Left auditory cortex is involved in pairwise comparisons of the direction of frequency modulated tones

Evaluating series of complex sounds like those in speech and music requires sequential comparisons to extract task-relevant relations between subsequent sounds. With the present functional magnetic resonance imaging (fMRI) study, we investigated whether sequential comparison of a specific acoustic feature within pairs of tones leads to a change in lateralized processing in the auditory cortex (AC) of humans. For this we used the active categorization of the direction (up vs. down) of slow frequency modulated (FM) tones. Several studies suggest that this task is mainly processed in the right AC. These studies, however, tested only the categorization of the FM direction of each individual tone. In the present study we ask the question whether the right lateralized processing changes when, in addition, the FM direction is compared within pairs of successive tones. For this we use an experimental approach involving contralateral noise presentation in order to explore the contributions made by the left and right AC in the completion of the auditory task. This method has already been applied to confirm the right-lateralized processing of the FM direction of individual tones. In the present study, the subjects were required to perform, in addition, a sequential comparison of the FM direction in pairs of tones. The results suggest a division of labor between the two hemispheres such that the FM direction of each individual tone is mainly processed in the right AC whereas the sequential comparison of this feature between tones in a pair is probably performed in the left AC.

Neural correlates of sound localization in complex acoustic environments

Listening to and understanding people in a “cocktail-party situation” is a remarkable feature of the human auditory system. Here we investigated the neural correlates of the ability to localize a particular sound among others in an acoustically cluttered environment with healthy subjects. In a sound localization task, five different natural sounds were presented from five virtual spatial locations during functional magnetic resonance imaging (fMRI). Activity related to auditory stream segregation was revealed in posterior superior temporal gyrus bilaterally, anterior insula, supplementary motor area, and frontoparietal network. Moreover, the results indicated critical roles of left planum temporale in extracting the sound of interest among acoustical distracters and the precuneus in orienting spatial attention to the target sound. We hypothesized that the left-sided lateralization of the planum temporale activation is related to the higher specialization of the left hemisphere for analysis of spectrotemporal sound features. Furthermore, the precuneus − a brain area known to be involved in the computation of spatial coordinates across diverse frames of reference for reaching to objects − seems to be also a crucial area for accurately determining locations of auditory targets in an acoustically complex scene of multiple sound sources. The precuneus thus may not only be involved in visuo-motor processes, but may also subserve related functions in the auditory modality.

Effects of L-dopa during auditory instrumental learning in humans

The dopaminergic neurotransmitter system is critically involved in promoting plasticity in auditory cortex. We combined functional magnetic resonance imaging (fMRI) and a pharmacological manipulation to investigate dopaminergic modulation of neural activity in auditory cortex during instrumental learning. Volunteers either received 100 mg L-dopa (Madopar) or placebo in an appetitive, differential instrumental conditioning paradigm, which involved learning that a specific category of frequency modulated tones predicts a monetary reward when fast responses were made in a subsequent reaction time task. The other category of frequency modulated tones was not related to a reward. Our behavioral data provides evidence that dopaminergic stimulation differentially impacts on the speed of instrumental responding in rewarded and unrewarded trials. L-dopa increased neural BOLD activity in left auditory cortex to tones in rewarded and unrewarded trials. This increase was related to plasma L-dopa levels and learning rate. Our data thus provides evidence for dopaminergic modulation of neural activity in auditory cortex, which occurs for both auditory stimuli related to a later reward and those not related to a reward.

The Role of Broca's Area in Sentence Comprehension

The role of Broca's area in sentence processing has been debated for the last 30 years. A central and still unresolved issue is whether Broca's area plays a specific role in some aspect of syntactic processing (e.g., syntactic movement, hierarchical structure building) or whether it serves a more general function on which sentence processing relies (e.g., working memory). This review examines the functional organization of Broca's area in regard to its contributions to sentence comprehension, verbal working memory, and other multimodal cognitive processes. We suggest that the data are consistent with the view that at least a portion of the contribution of Broca's area to sentence comprehension can be attributed to its role as a phonological short-term memory resource. Furthermore, our review leads us to conclude that there is no compelling evidence that there are sentence-specific processing regions within Broca's area.

Neural mechanisms of auditory discrimination of long-duration tonal patterns: a neural modeling and fMRI study

Language perception comprises mechanisms of perception and discrimination of auditory stimuli. An important component of auditory perception and discrimination concerns auditory objects. Many interesting auditory objects in our environment are of relatively long duration; however, the temporal window of integration of auditory cortex neurons processing these objects is very limited. Thus, it is necessary to make active use of short-term memory in order to construct and temporarily store long-duration objects. We sought to understand the mechanisms by which the brain manipulates long-duration tonal patterns, temporarily stores the segments of those patterns, and integrates them into an auditory object. We extended a previously constructed model of auditory recognition of short-duration tonal patterns by expanding the prefrontal cortically-based short-term memory module of the previous model into a memory buffer with multiple short-term memory submodules and by adding a gating module. The gating module distributes the segments of the input pattern to separate locations of the extended prefrontal cortex in an orderly fashion, allowing a subsequent comparison of the stored segments against the segments of a second pattern. In addition to simulating behavioral data and electrical activity of neurons, our model also produces simulations of the blood oxygen level dependent (BOLD) signal as obtained in fMRI studies. The results of these simulations provided us with predictions that we tested in an fMRI experiment with normal volunteers. This fMRI experiment used the same task and similar stimuli to that of the model. We compared simulated data with experimental values. We found that two brain areas, the right precentral gyrus and the left medial frontal gyrus, correlated well with our simulations of the memory gating module. Other fMRI studies of auditory perception and discrimination have also found correlation of fMRI activation of those areas with similar tasks and thus provide further support to our findings.

Cross-cultural music phrase processing: an fMRI study

The current study used functional magnetic resonance imaging (fMRI) to investigate the neural basis of musical phrase boundary processing during the perception of music from native and non-native cultures. German musicians performed a cultural categorization task while listening to phrased Western (native) and Chinese (non-native) musical excerpts as well as modified versions of these, where the impression of phrasing has been reduced by removing the phrase boundary marking pause (henceforth called "unphrased"). Bilateral planum temporale was found to be associated with an increased difficulty of identifying phrase boundaries in unphrased Western melodies. A network involving frontal and parietal regions showed increased activation for the phrased condition with the orbital part of left inferior frontal gyrus presumably reflecting working memory aspects of the temporal integration between phrases, and the middle frontal gyrus and intraparietal sulcus probably reflecting attention processes. Areas more active in the culturally familiar, native (Western) condition included, in addition to the left planum temporale and right ventro-medial prefrontal cortex, mainly the bilateral motor regions. These latter results are interpreted in light of sensorimotor integration. Regions with increased signal for the unfamiliar, non-native music style (Chinese) included a right lateralized network of angular gyrus and the middle frontal gyrus, possibly reflecting higher demands on attention systems, and the right posterior insula suggesting higher loads on basic auditory processing.

The superior temporal sulcus performs a common function for social and speech perception: implications for the emergence of autism

Within the cognitive neuroscience literature, discussion of the functional role of the superior temporal sulcus (STS) has traditionally been divided into two domains; one focuses on its activity during language processing while the other emphasizes its role in biological motion and social attention, such as eye gaze processing. I will argue that a common process underlying both of these functional domains is performed by the STS, namely analyzing changing sequences of input, either in the auditory or visual domain, and interpreting the communicative significance of those inputs. From a developmental perspective, the fact that these two domains share an anatomical substrate suggests the acquisition of social and speech perception may be linked. In addition, I will argue that because of the STS' role in interpreting social and speech input, impairments in STS function may underlie many of the social and language abnormalities seen in autism.

Laminar specificity of intrinsic connections in Broca's area

Broca's area and its right hemisphere homologue comprise 2 cytoarchitectonic subdivisions, FDgamma and FCBm of von Economo C and Koskinas GN (1925, Die Cytoarchitektonik der Hirnrinde des erwachsenen Menschen. Vienna/Berlin [Germany]: Springer). We report here on intrinsic connections within these areas, as revealed with biotinylated dextran amine and 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate tracing in postmortem human brains. Injections limited to supragranular layers revealed a complex intrinsic network of horizontal connections within layers II and III spreading over several millimeters and to a lesser extent within layers IV, V, and VI. Ninety percent of the retrogradely labeled neurons (n = 734) were in supragranular layers, 4% in layer IV, and 6% in infragranular layers; most were pyramids and tended to be grouped into clusters of approximately 500 microm in diameter. Injections involving layer IV revealed extended horizontal connections within layers I-IV (up to 3.7 mm) and to a lesser extent in layers V and VI. Injections limited to the infragranular layers revealed horizontal connections mainly limited to these layers. Thus, intrinsic connections within Broca's area display a strong laminar specificity. This pattern is very similar in areas FDgamma and FCBm and in the 2 hemispheres.

Auditory processing, speech perception and phonological ability in pre-school children at high-risk for dyslexia: A longitudinal study of the auditory temporal processing theory

This study investigates whether the core bottleneck of literacy-impairment should be situated at the phonological level or at a more basic sensory level, as postulated by supporters of the auditory temporal processing theory. Phonological ability, speech perception and low-level auditory processing were assessed in a group of 5-year-old pre-school children at high-family risk for dyslexia, compared to a group of well-matched low-risk control children. Based on family risk status and first grade literacy achievement children were categorized in groups and pre-school data were retrospectively reanalyzed. On average, children showing both increased family risk and literacy-impairment at the end of first grade, presented significant pre-school deficits in phonological awareness, rapid automatized naming, speech-in-noise perception and frequency modulation detection. The concurrent presence of these deficits before receiving any formal reading instruction, might suggest a causal relation with problematic literacy development. However, a closer inspection of the individual data indicates that the core of the literacy problem is situated at the level of higher-order phonological processing. Although auditory and speech perception problems are relatively over-represented in literacy-impaired subjects and might possibly aggravate the phonological and literacy problem, it is unlikely that they would be at the basis of these problems. At a neurobiological level, results are interpreted as evidence for dysfunctional processing along the auditory-to-articulation stream that is implied in phonological processing, in combination with a relatively intact or inconsistently impaired functioning of the auditory-to-meaning stream that subserves auditory processing and speech perception.

Activation of premotor vocal areas during musical discrimination

Two same/different discrimination tasks were performed by amateur-musician subjects in this functional magnetic resonance imaging study: Melody Discrimination and Harmony Discrimination. Both tasks led to activations not only in classic working memory areas--such as the cingulate gyrus and dorsolateral prefrontal cortex--but in a series of premotor areas involved in vocal-motor planning and production, namely the somatotopic mouth region of the primary and lateral premotor cortices, Broca's area, the supplementary motor area, and the anterior insula. A perceptual control task involving passive listening alone to monophonic melodies led to activations exclusively in temporal-lobe auditory areas. These results show that, compared to passive listening tasks, discrimination tasks elicit activation in vocal-motor planning areas.

Hand actions and speech representation in Broca's area

This paper presents data and theoretical framework supporting a new interpretation of the role played by Broca's area. Recent brain imaging studies report that, in addition to speech-related activation, Broca's area is also significantly involved during tasks devoid of verbal content. In consideration of the large variety of experimental paradigms inducing Broca's activation, here we present some neurophysiological data from the monkey homologue of Brodmann's areas (BA) 44 and 45 aiming to integrate on a common ground these apparently different functions. Finally, we will report electrophysiological data on humans which connect speech perception to the more general framework of other's action understanding.

Cognitive priming in sung and instrumental music: Activation of inferior frontal cortex

Neural correlates of the processing of musical syntax-like structures have been investigated via expectancy violation due to musically unrelated (i.e., unexpected) events in musical contexts. Previous studies reported the implication of inferior frontal cortex in musical structure processing. However - due to the strong musical manipulations - activations might be explained by sensory deviance detection or repetition priming. Our present study investigated neural correlates of musical structure processing with subtle musical violations in a musical priming paradigm. Instrumental and sung sequences ended on related and less-related musical targets. The material controlled sensory priming components, and differences in target processing required listeners' knowledge on musical structures. Participants were scanned with functional Magnetic Resonance Imaging (fMRI) while performing speeded phoneme and timbre identification judgments on the targets. Behavioral results acquired in the scanner replicated the facilitation effect of related over less-related targets. The blood oxygen level-dependent (BOLD) signal linked to target processing revealed activation of right inferior frontal areas (i.e., inferior frontal gyrus, frontal operculum, anterior insula) that was stronger for less-related than for related targets, and this was independent of the material carrying the musical structures. This outcome points to the implication of inferior frontal cortex in the processing of syntactic relations also for musical material and to its role in the processing and integration of sequential information over time. In addition to inferior frontal activation, increased activation was observed in orbital gyrus, temporal areas (anterior superior temporal gyrus, posterior superior temporal gyrus and sulcus, posterior middle temporal gyrus) and supramarginal gyrus.

Top-down and bottom-up processes in speech comprehension

Speech comprehension includes both bottom-up and top-down processes, and imaging studies have isolated a frontal-temporal network of brain areas active during speech perception. However, the precise role of the various areas in this network during normal speech comprehension is not yet fully understood. In the present fMRI study, the signal-to-noise ratio (SNR) of spoken sentences was varied in 144 steps, and speech intelligibility was measured independently in order to study in detail its effect on the activation of brain areas involved in speech perception. Relative to noise alone, intelligible speech in noise evoked spatially extended activation in left frontal, bilateral temporal, and medial occipital brain regions. Increasing SNR led to a sigmoid-shaped increase of activation in all areas of the frontal-temporal network. The onset of the activation with respect to SNR was similar in temporal and frontal regions, but frontal activation was found to be smaller than temporal activation at the highest SNRs. Finally, only Broca's area (BA44) showed activation to unintelligible speech presented at low SNRs. These findings demonstrate distinct roles of frontal and temporal areas in speech comprehension in that temporal regions subserve bottom-up processing of speech, whereas frontal areas are more involved in top-down supplementary mechanisms.

Functional Neuroanatomy of Segmenting Speech and Nonspeech

This fMRI study investigates the extent to which frontal brain activation observed during speech discrimination is due to processes specific to articulatory recoding of speech or is due to segmenting and comparing portions of any continuous acoustic stimuli. A set of ten participants performed same/different judgments on the first speech sound in pairs of consonant-vowel-consonant (CVC) syllables or the first tone in pairs of sequences of three tones. Comparison between speech and tone tasks demonstrated significant bilateral temporal activation, which was associated with differences in perceptual analysis of complex acoustic stimuli. Both speech and tone tasks also showed significant activation in the left inferior frontal gyrus (IFG) compared to baseline. These results suggest that portions of the left prefrontal cortex may be important for selecting and comparing auditory stimuli for decision, but may not be specifically related to speech.

The functional organization of auditory working memory as revealed by fMRI

Spatial and nonspatial auditory tasks preferentially recruit dorsal and ventral brain areas, respectively. However, the extent to which these auditory differences reflect specific aspects of mental processing has not been directly studied. In the present functional magnetic resonance imaging experiment, participants encoded and maintained either the location or the identity of a sound for a delay period of several seconds and then subsequently compared that information with a second sound. Relative to sound localization, sound identification was associated with greater hemodynamic activity in the left rostral superior temporal gyrus. In contrast, localizing sounds recruited greater activity in the parietal cortex, posterior temporal lobe, and superior frontal sulcus. The identification differences were most prominent during the early stage of the trial, whereas the location differences were most evident during the late (i.e., comparison) stage. Accordingly, our results suggest that auditory spatial and identity dissociations as revealed by functional imaging may be dependent to some degree on the type of processing being carried out. In addition, dorsolateral prefrontal and lateral superior parietal areas showed greater activity during the comparison as opposed to the earlier stage of the trial, regardless of the type of auditory task, consistent with results from visual working memory studies.

A systematic investigation of the functional neuroanatomy of auditory and visual phonological processing

Neuroimaging studies of auditory and visual phonological processing have revealed activation of the left inferior and middle frontal gyri. However, because of task differences in these studies (e.g., consonant discrimination versus rhyming), the extent to which this frontal activity is due to modality-specific linguistic processes or to more general task demands involved in the comparison and storage of stimuli remains unclear. An fMRI experiment investigated the functional neuroanatomical basis of phonological processing in discrimination and rhyming tasks across auditory and visual modalities. Participants made either "same/different" judgments on the final consonant or rhyme judgments on auditorily or visually presented pairs of words and pseudowords. Control tasks included "same/different" judgments on pairs of single tones or false fonts and on the final member in pairs of sequences of tones or false fonts. Although some regions produced expected modality-specific activation (i.e., left superior temporal gyrus in auditory tasks, and right lingual gyrus in visual tasks), several regions were active across modalities and tasks, including posterior inferior frontal gyrus (BA 44). Greater articulatory recoding demands for processing of pseudowords resulted in increased activation for pseudowords relative to other conditions in this frontal region. Task-specific frontal activation was observed for auditory pseudoword final consonant discrimination, likely due to increased working memory demands of selection (ventrolateral prefrontal cortex) and monitoring (mid-dorsolateral prefrontal cortex). Thus, the current study provides a systematic comparison of phonological tasks across modalities, with patterns of activation corresponding to the cognitive demands of performing phonological judgments on spoken and written stimuli.

Specific language impairment is not specific to language: the procedural deficit hypothesis

Specific Language Impairment (SLI) has been explained by two broad classes of hypotheses, which posit either a deficit specific to grammar, or a non-linguistic processing impairment. Here we advance an alternative perspective. According to the Procedural Deficit Hypothesis (PDH), SLI can be largely explained by the abnormal development of brain structures that constitute the procedural memory system. This system, which is composed of a network of inter-connected structures rooted in frontal/basal-ganglia circuits, subserves the learning and execution of motor and cognitive skills. Crucially, recent evidence also implicates this system in important aspects of grammar. The PDH posits that a significant proportion of individuals with SLI suffer from abnormalities of this brain network, leading to impairments of the linguistic and non-linguistic functions that depend on it. In contrast, functions such as lexical and declarative memory, which depend on other brain structures, are expected to remain largely spared. Evidence from an in-depth retrospective examination of the literature is presented. It is argued that the data support the predictions of the PDH, and particularly implicate Broca's area within frontal cortex, and the caudate nucleus within the basal ganglia. Finally, broader implications are discussed, and predictions for future research are presented. It is argued that the PDH forms the basis of a novel and potentially productive perspective on SLI.

AChE-rich magnopyramidal neurons have a left–right size asymmetry in Broca's area

Acetylcholinesterase-rich neurons (AChERN) are a particular group of pyramidal neurons, displaying a specific laminar and ontogenetic pattern in the cerebral cortex of human and nonhuman primates. Using histochemistry and morphometrical methods, we have found a layer 3 magnopyramidal AChERN left-right size asymmetry restricted to Brodmann's area 45, a component of Broca's language area. This structural feature could be related to functional lateralization associated to syntactic processing and phonological working memory, and is consistent with a non-cholinergic role of AChE possibly linked to neuroplastic processes in the human neocortex.

An fMRI Investigation of Speech and Tone Segmentation

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

Hemispheric shifts of sound representation in auditory cortex with conceptual listening

The weak field specificity and the heterogeneity of neuronal filters found in any given auditory cortex field does not substantiate the view that such fields are merely descriptive maps of sound features. But field mechanisms were previously shown to support behaviourally relevant classification of sounds. Here the prediction was tested in human auditory cortex (AC) that classification-tasks rather than the stimulus class per se determine which auditory cortex area is recruited. By presenting the same set of frequency-modulations we found that categorization of their pitch direction (rising versus falling) increased functional magnetic resonance imaging activation in right posterior AC compared with stimulus exposure and in contrast to left posterior AC dominance during categorization of their duration (short versus long). Thus, top-down influences appear to select not only auditory cortex areas but also the hemisphere for specific processing.

Assessing the auditory dual-pathway model in humans

Evidence from anatomical and neurophysiological studies in nonhuman primates suggests a dual-pathway model of auditory processing wherein sound identity and sound location information are segregated along ventral and dorsal streams, respectively. The present meta-analysis reviewed evidence from auditory functional magnetic resonance imaging (fMRI) and positron emission tomography (PET) studies to determine the reliability of this model in humans. Activation coordinates from 11 "spatial" studies (i.e., listeners made localization judgements on sounds that could occur at two or more perceptually different positions) and 27 "nonspatial" studies (i.e., listeners completed nonspatial tasks involving sounds presented from the same location) were entered into the analysis. All but one of the spatial studies reported activation within the inferior parietal lobule as opposed to only 41% of the nonspatial studies. In addition, 55% of spatial studies reported activity around the superior frontal sulcus as opposed to only 7% of the nonspatial studies. In comparison, inferior frontal activity (Brodmann's areas 45 and 47) was reported in only 9% of the spatial studies, but in 56% of the nonspatial studies. Finally, almost all temporal lobe activity observed during spatial tasks was confined to posterior areas, whereas nonspatial activity was distributed throughout the temporal lobe. These results support an auditory dual-pathway model in humans in which nonspatial sound information (e.g., sound identity) is processed primarily along the ventral stream whereas sound location is processed along the dorsal stream and areas posterior to primary auditory cortex.

Are nonlinguistic functions in "Broca's area" prerequisites for language acquisition? FMRI findings from an ontogenetic viewpoint

There is incomplete consensus on the anatomical demarcation of Broca's area in the left inferior frontal gyrus and its functional characterization remains a matter of debate. Exclusive syntactic specialization has been proposed, but is overall inconsistent with the neuroimaging literature. We examined three functional MRI (fMRI) datasets on lexicosemantic decision, tone discrimination, and visuomotor coordination for potential overlap of activation. A single site of convergent activation across all three paradigms was found in the left inferior frontal lobe (area 44/45). This result is discussed in the context of animal and human studies showing inferior frontal participation in visuomotor and audiomotor functions as well as working memory. We propose that Broca's area involvement in lexical semantics and syntax emerges from these nonlinguistic functions, which are prerequisites for language acquisition.

Activation of the Inferior Frontal Cortex in Musical Priming

Musical contexts influence the processing of target events. Our study investigated the neural correlates of processing related and unrelated musical events presented as the last chord of eight-chord sequences.

Linguistic theory and neuroimaging evidence: an fMRI study of Broca's area in lexical semantics

There has been a long debate on the functional characterization of left inferior frontal cortex, including proposals regarding syntactic and lexico-semantic involvement. We studied nine right-handed adults, using functional magnetic resonance imaging (fMRI) during performance on a semantic decision task in which subjects had to determine whether noun-verb pairs were semantically associated. In comparison with a visuoperceptual control task, activation clusters were seen in left inferior frontal and middle temporal regions, as well as the bilateral superior frontal gyrus. In agreement with previous studies, our findings suggest that Broca's area is involved in semantic processing. Findings of lexico-semantic as well as syntactic processing in the inferior frontal lobe may be accounted for in terms of working memory demands.

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.

Activation of the inferior frontal cortex in musical priming

Behavioral studies have provided evidence that the processing of a musical target is faster and more accurate when it is harmonically related to the preceding prime context. We investigated the neural correlates of processing related and unrelated musical targets that were presented at the end of musical sequences. Participants were scanned with functional magnetic resonance imaging (fMRI) while performing speeded intonation judgments (consonant versus dissonant) on the target chords. Behavioral results acquired in the scanner replicated the facilitation effect of related over unrelated consonant targets. The overall activation pattern associated with target processing showed commonalities with networks previously described for target detection and novelty processing. The blood oxygen level-dependent (BOLD) signal linked to target processing revealed activation of bilateral inferior frontal regions (i.e. inferior frontal gyrus, frontal operculum, insula) that was stronger for unrelated than for related targets. We discuss our results with regard to the role of these areas in the processing and integration of temporal information.

Functional MRI of language: new approaches to understanding the cortical organization of semantic processing

Until recently, our understanding of how language is organized in the brain depended on analysis of behavioral deficits in patients with fortuitously placed lesions. The availability of functional magnetic resonance imaging (fMRI) for in vivo analysis of the normal brain has revolutionized the study of language. This review discusses three lines of fMRI research into how the semantic system is organized in the adult brain. These are (a) the role of the left inferior frontal lobe in semantic processing and dissociations from other frontal lobe language functions, (b) the organization of categories of objects and concepts in the temporal lobe, and (c) the role of the right hemisphere in comprehending contextual and figurative meaning. Together, these lines of research broaden our understanding of how the brain stores, retrieves, and makes sense of semantic information, and they challenge some commonly held notions of functional modularity in the language system.

Functional MRI of motor sequence acquisition: effects of learning stage and performance

Neural networks of motor control are well understood and the motor domain therefore lends itself to the study of learning. Neuroimaging of motor learning has demonstrated fronto-parietal, subcortical, and cerebellar involvement. However, there is conflicting evidence on the specific functional contributions of individual regions and their relative importance for early and advanced stages of learning. Using functional MRI (fMRI), we examined hemodynamic effects in seven right-handed men during brief episodes of explicit learning of novel six-digit sequences (experiments 1 and 2) and during prolonged learning of an eight-digit sequence (experiment 3), all performed with the dominant hand. Brief episodes of new learning were predominantly associated with bilateral activations in premotor and supplementary motor areas, superior and inferior parietal cortices, and anterior cerebellum. In experiment 2, which included a control condition matched for complexity of motor execution, we also found unexpectedly strong activation in the bilateral inferior frontal lobes. In experiment 3, analysis of task by learning stage interactions showed greater involvement of the bilateral superior parietal lobes, the right middle frontal gyrus, and the left caudate nucleus during early stages, whereas left occipito-temporal and superior frontal cortex as well as the bilateral parahippocampal region were more activated during late learning stages. Analysis of task by performance interactions (based on each subject's response times and accuracy during each scan) showed effects in bilateral fronto-polar, right hippocampal, and anterior cerebellar regions associated with high levels of performance, as well as inverse effects in bilateral occipito-parietal regions. We conclude that superior parietal and occipital regions are most intensely involved in visually driven explicit digit sequence learning during early stages and low performance, whereas later stages of acquisition and higher levels of performance are characterized by stronger recruitment of prefrontal and mediotemporal regions.

A comparison of neural circuits underlying auditory and visual object categorization

Knowledge about environmental objects derives from representations of multiple object features both within and across sensory modalities. While our understanding of the neural basis for visual object representation in the human and nonhuman primate brain is well advanced, a similar understanding of auditory objects is in its infancy. We used a name verification task and functional magnetic resonance imaging (fMRI) to characterize the neural circuits that are activated as human subjects match visually presented words with either simultaneously presented pictures or environmental sounds. The difficulty of the matching judgment was manipulated by varying the level of semantic detail at which the words and objects were compared. We found that blood oxygen level dependent (BOLD) signal was modulated in ventral and dorsal regions of the inferior frontal gyrus of both hemispheres during auditory and visual object categorization, potentially implicating these areas as sites for integrating polymodal object representations with concepts in semantic memory. As expected, BOLD signal increases in the fusiform gyrus varied with the semantic level of object categorization, though this effect was weak and restricted to the left hemisphere in the case of auditory objects.

Listening to polyphonic music recruits domain-general attention and working memory circuits

Polyphonic music combines multiple auditory streams to create complex auditory scenes, thus providing a tool for investigating the neural mechanisms that orient attention in natural auditory contexts. Across two fMRI experiments, we varied stimuli and task demands in order to identify the cortical areas that are activated during attentive listening to real music. In individual experiments and in a conjunction analysis of the two experiments, we found bilateral blood oxygen level dependent (BOLD) signal increases in temporal (the superior temporal gyrus), parietal (the intraparietal sulcus), and frontal (the precentral sulcus, the inferior frontal sulcus and gyrus, and the frontal operculum) areas during selective and global listening, as compared with passive rest without musical stimulation. Direct comparisons of the listening conditions showed significant differences between attending to single timbres (instruments) and attending across multiple instruments, although the patterns that were observed depended on the relative demands of the tasks being compared. The overall pattern of BOLD signal increases indicated that attentive listening to music recruits neural circuits underlying multiple forms of working memory, attention, semantic processing, target detection, and motor imagery. Thus, attentive listening to music appears to be enabled by areas that serve general functions, rather than by music-specific cortical modules.

Current awareness

In order to keep subscribers up-to-date with the latest developments in their field, John Wiley & Sons are providing a current awareness service in each issue of the journal. The bibliography contains newly published material in the field of NMR in biomedicine. Each bibliography is divided into 9 sections: 1 Books, Reviews ' Symposia; 2 General; 3 Technology; 4 Brain and Nerves; 5 Neuropathology; 6 Cancer; 7 Cardiac, Vascular and Respiratory Systems; 8 Liver, Kidney and Other Organs; 9 Muscle and Orthopaedic. Within each section, articles are listed in alphabetical order with respect to author. If, in the preceding period, no publications are located relevant to any one of these headings, that section will be omitted.