Multimodal Convergence Research Articles

Electrophysiological responses to appetitive and consummatory behavior in the rostral nucleus tractus solitarius in awake, unrestrained rats.

As the intermediate nucleus in the brainstem receiving information from the tongue and transmitting information upstream, the rostral portion of the nucleus tractus solitarius (rNTS) is most often described as a "taste relay". Although recent evidence implicates the caudal NTS in a broad neural circuit involved in regulating ingestion, there is little information about how cells in the rNTS respond when an animal is eating solid food. Single cells in the rNTS were recorded in awake, unrestrained rats as they explored and ate solid foods (Eating paradigm) chosen to correspond to the basic taste qualities: milk chocolate for sweet, salted peanuts for salty, Granny Smith apples for sour and broccoli for bitter. A subset of cells was also recorded as the animal licked exemplars of the five basic taste qualities: sucrose, NaCl, citric acid, quinine and MSG (Lick paradigm). Most cells were excited by exploration of a food-filled well, sometimes responding prior to contact with the food. In contrast, cells that were excited by food well exploration became significantly less active while the animal was eating the food. Most cells were broadly tuned across foods, and those cells that were recorded in both the Lick and Eating paradigms showed little correspondence in their tuning across paradigms. The preponderance of robust responses to the appetitive versus the consummatory phase of ingestion suggests that multimodal convergence onto cells in the rNTS may be used in decision making about ingestion.

Multimodal convergence in the pedunculopontine tegmental nucleus: Motor, sensory and theta-frequency inputs influence activity of single neurons.

The pedunculopontine tegmental nucleus of the brainstem (PPTg) has extensive interconnections and neuronal-behavioural correlates. It is implicated in movement control and sensorimotor integration. We investigated whether single neuron activity in freely moving rats is correlated with components of skilled forelimb movement, and whether individual neurons respond to both motor and sensory events. We found that individual PPTg neurons showed changes in firing rate at different times during the reach. This type of temporally specific modulation is like activity seen elsewhere in voluntary movement control circuits, such as the motor cortex, and suggests that PPTg neural activity is related to different specific events occurring during the reach. In particular, many neuronal modulations were time-locked to the end of the extension phase of the reach, when fine distal movements related to food grasping occur, indicating strong engagement of PPTg in this phase of skilled individual forelimb movements. In addition, some neurons showed brief periods of apparent oscillatory firing in the theta range at specific phases of the reach-to-grasp movement. When movement-related neurons were tested with tone stimuli, many also responded to this auditory input, allowing for sensorimotor integration at the cellular level. Together, these data extend the concept of the PPTg as an integrative structure in generation of complex movements, by showing that this function extends to the highly coordinated control of the forelimb during skilled reach to grasp movement, and that sensory and motor-related information converges on single neurons, allowing for direct integration at the cellular level.

The role of the angular gyrus in semantic cognition: a synthesis of five functional neuroimaging studies

Semantic knowledge is central to human cognition. The angular gyrus (AG) is widely considered a key brain region for semantic cognition. However, the role of the AG in semantic processing is controversial. Key controversies concern response polarity (activation vs. deactivation) and its relation to task difficulty, lateralization (left vs. right AG), and functional–anatomical subdivision (PGa vs. PGp subregions). Here, we combined the fMRI data of five studies on semantic processing (n = 172) and analyzed the response profiles from the same anatomical regions-of-interest for left and right PGa and PGp. We found that the AG was consistently deactivated during non-semantic conditions, whereas response polarity during semantic conditions was inconsistent. However, the AG consistently showed relative response differences between semantic and non-semantic conditions, and between different semantic conditions. A combined analysis across all studies revealed that AG responses could be best explained by separable effects of task difficulty and semantic processing demand. Task difficulty effects were stronger in PGa than PGp, regardless of hemisphere. Semantic effects were stronger in left than right AG, regardless of subregion. These results suggest that the AG is engaged in both domain-general task-difficulty-related processes and domain-specific semantic processes. In semantic processing, we propose that left AG acts as a “multimodal convergence zone” that binds different semantic features associated with the same concept, enabling efficient access to task-relevant features.

Task-Dependent Functional and Effective Connectivity during Conceptual Processing.

Conceptual knowledge is central to cognition. Previous neuroimaging research indicates that conceptual processing involves both modality-specific perceptual-motor areas and multimodal convergence zones. For example, our previous functional magnetic resonance imaging (fMRI) study revealed that both modality-specific and multimodal regions respond to sound and action features of concepts in a task-dependent fashion (Kuhnke P, Kiefer M, Hartwigsen G. 2020b. Task-dependent recruitment of modality-specific and multimodal regions during conceptual processing. Cereb Cortex. 30:3938–3959.). However, it remains unknown whether and how modality-specific and multimodal areas interact during conceptual tasks. Here, we asked 1) whether multimodal and modality-specific areas are functionally coupled during conceptual processing, 2) whether their coupling depends on the task, 3) whether information flows top-down, bottom-up or both, and 4) whether their coupling is behaviorally relevant. We combined psychophysiological interaction analyses with dynamic causal modeling on the fMRI data of our previous study. We found that functional coupling between multimodal and modality-specific areas strongly depended on the task, involved both top-down and bottom-up information flow, and predicted conceptually guided behavior. Notably, we also found coupling between different modality-specific areas and between different multimodal areas. These results suggest that functional coupling in the conceptual system is extensive, reciprocal, task-dependent, and behaviorally relevant. We propose a new model of the conceptual system that incorporates task-dependent functional interactions between modality-specific and multimodal areas.

Time is body: Multimodal evidence of crosstalk between interoception and time estimation

Theoretical approaches propose a blending between interoception and time estimation. Interoception might constitute a neurophysiological mechanism for encoding duration. However, no study has assessed the convergence between interoception and time estimation using behavioral, neurophysiological, and functional anatomy signatures. We examined the multimodal convergence between interoception and time estimation using a two-fold approach. In study 1, we developed a dual design combining interoception (measuring heartbeat detection - HBD, and heartbeat evoked potential - HEP) with a time estimation paradigm (TEP, estimation of duration of a 120 s interval). In study 2, we performed a conjoint metanalysis (Multi-level Kernel Density Analysis, MKDA) of neuroimaging, including reports of interoception and time estimation. Both studies provide convergent evidence of time estimation's significant involvement in behavioral, electrophysiological (enhanced HEP), and neuroimaging (overlapping cluster in the right insula and operculum) signatures of interoception. Convergent results from both studies offer direct support for a shared mechanism of interoception and time estimation.

How to Teach DNNs to Pay Attention to the Visual Modality in Speech Recognition

Audio-Visual Speech Recognition (AVSR) seeks to model, and thereby exploit, the dynamic relationship between a human voice and the corresponding mouth movements. A recently proposed multimodal fusion strategy, AV Align, based on state-of-the-art sequence to sequence neural networks, attempts to model this relationship by explicitly aligning the acoustic and visual representations of speech. This study investigates the inner workings of AV Align and visualises the audio-visual alignment patterns. Our experiments are performed on two of the largest publicly available AVSR datasets, TCD-TIMIT and LRS2. We find that AV Align learns to align acoustic and visual representations of speech at the frame level on TCD-TIMIT in a generally monotonic pattern. We also determine the cause of initially seeing no improvement over audio-only speech recognition on the more challenging LRS2. We propose a regularisation method which involves predicting lip-related Action Units from visual representations. Our regularisation method leads to better exploitation of the visual modality, with performance improvements between 7% and 30% depending on the noise level. Furthermore, we show that the alternative Watch, Listen, Attend, and Spell network is affected by the same problem as AV Align, and that our proposed approach can effectively help it learn visual representations. Our findings validate the suitability of the regularisation method to AVSR and encourage researchers to rethink the multimodal convergence problem when having one dominant modality.

Multimodal conceptual knowledge influences lexical retrieval speed: evidence from object-naming and word-reading in healthy adults

Multimodal conceptual knowledge influences lexical retrieval speed: evidence from object-naming and word-reading in healthy adults

Multimodal Interactions between Proprioceptive and Cutaneous Signals in Primary Somatosensory Cortex

The classical view of somatosensory processing holds that proprioceptive and cutaneous inputs are conveyed to cortex through segregated channels, initially synapsing in modality-specific areas 3a (proprioception) and 3b (cutaneous) of primary somatosensory cortex (SI). These areas relay their signals to areas 1 and 2 where multimodal convergence first emerges. However, proprioceptive and cutaneous maps have traditionally been characterized using unreliable stimulation tools. Here, we employed a mechanical stimulator that reliably positioned animals' hands in different postures and presented tactile stimuli with superb precision. Single-unit recordings in SI revealed that most neurons responded to cutaneous and proprioceptive stimuli, including cells in areas 3a and 3b. Multimodal responses were characterized by linear and nonlinear effects that emerged during early (∼20 ms) and latter (> 100 ms) stages of stimulus processing, respectively. These data are incompatible with the modality specificity model in SI, and provide evidence for distinct mechanisms of multimodal processing in the somatosensory system.

A multilevel multimodal circuit enhances action selection in Drosophila

Natural events present multiple types of sensory cues, each detected by a specialized sensory modality. Combining information from several modalities is essential for the selection of appropriate actions. Key to understanding multimodal computations is determining the structural patterns of multimodal convergence and how these patterns contribute to behaviour. Modalities could converge early, late or at multiple levels in the sensory processing hierarchy. Here we show that combining mechanosensory and nociceptive cues synergistically enhances the selection of the fastest mode of escape locomotion in Drosophila larvae. In an electron microscopy volume that spans the entire insect nervous system, we reconstructed the multisensory circuit supporting the synergy, spanning multiple levels of the sensory processing hierarchy. The wiring diagram revealed a complex multilevel multimodal convergence architecture. Using behavioural and physiological studies, we identified functionally connected circuit nodes that trigger the fastest locomotor mode, and others that facilitate it, and we provide evidence that multiple levels of multimodal integration contribute to escape mode selection. We propose that the multilevel multimodal convergence architecture may be a general feature of multisensory circuits enabling complex input-output functions and selective tuning to ecologically relevant combinations of cues.

Multi-modal convergence maps: from body schema and self-representation to mental imagery

Understanding the world involves extracting the regularities that define the interaction of the behaving organism within this world, and computing the statistical structure characterizing these regularities. This can be based on contingencies of phenomena at various scales ranging from correlations between sensory signals (e.g., motor-proprioceptive loops) to high-level conceptual links (e.g., vocabulary grounding). Multiple cortical areas contain neurons whose receptive fields are tuned for signals co-occurring in multiple modalities. Moreover, the hierarchical organization of the cortex, described within the Convergence Divergence Zone framework, defines an ideal architecture to extract and make use of contingency at increasing levels of complexity. We present an artificial neural network model of the early cortical amodal computations, which we have demonstrated on the humanoid robot iCub. This model explains and predicts findings in neurophysiology and neuropsychology along with being an efficient tool to control the robot. In particular, through exploratory use of the body, the system learns a form of body schema in terms of specific modalities (e.g., arm proprioception, gaze proprioception, vision) and their multimodal contingencies. Once multimodal contingencies have been learned, the system is capable of generating and exploiting internal representations or mental images based on inputs in one of these multiple dimensions. The system thus provides insight on a possible neural substrate for mental imagery within the context of multimodal convergence.

Su1971 The Effects of Oxytocin on Gastric Motility are Mediated by Different Neuronal Pathways in an Iodoacetamide Model of Functional Dyspepsia

Background: Insula represents an important site in the brain for multi-modal convergence and has been implicated in processing of visceral sensation. Earlier fMRI studies in humans (Lawall, et al. Am J Physiol 2008;294:G787-94) have shown activation and sensitization of insula in response to esophageal acid stimulation. However, response characteristics of insular neurons to esophageal chemical and mechanical stimulation have not been studied. Aims: Our aims in this study were: (i) to determine the influence of esophageal acid stimulation on the insular cortex neurons (ICNs) and (ii) to characterize the responses of these neurons to esophageal distension (ED) and colorectal distension (CRD) before and after esophageal acid exposure. Methods: Eleven male rats (SD, 300-400g) were initially anaesthetized with a mixture of α-chloralose (80mg/kg, i.p.) + urethane (800mg/kg, i.p.). The anesthetics were periodically supplemented (i.v.) every 3 hours with one-fourth of the initial dose and the blood pressure was constantly monitored. A craniotomy (Bregma: +2.5 to -2.5 mm, 2.0 to 7.0 mm lateral) was performed to access insular cortex (IC). Extracellular recordings from the ICNs (Bregma: +1.8 to -2.2 mm, 5.0 to 7.4 mm lateral, 5.8 to 7.8 mm dorso-ventral) were made from the neurons that responded to ED (30-60 mmHg) and/or CRD (30-60 mmHg). After characterization of ICNs to visceral stimulation (ED and CRD), 0.1 ml of PBS (0.1M, pH 7.4) was infused slowly (0.1ml/min) into the esophagus followed by the same volume of 0.1N HCl (pH 1.2). The infusate (0.1 ml) was applied three times at 60s, 300s and 540s. The interval of each infusion time was 4 minutes. The ED and CRD were repeated 15 minutes after acid infusion to study the responses of neurons. Results: Fifteen ED or CRD sensitive neurons were studied for their responses to PBS and acid infusion. All neurons (15/15, 100%) exhibited excitation (p<0.05) following acid infusion, whereas PBS had no effect on the responses of these neurons. Eleven EDand 10 CRDresponsive neurons were fully characterized to preand post-acid condition. Following acid infusion, 11/11 (100%) ED-responsive neurons exhibited increased activity in response to ED. In contrast, 10/10 (100%) CRD-responsive neurons exhibited decreased activity during CRD. In addition, acid, but not PBS, infusion increased the spontaneous firing of all recorded neurons and continued for 30 to 45 minutes after cessation of infusion. Conclusions: Intraesophageal acid infusion significantly alters the response characteristics of ICNs in rats. Esophageal acid infusion differentially modulates the activities of ICNs that receive convergent input from esophagus and colon.

Su1970 Effects of Oxytocin on Gastric-Projecting Neurons in a Rat Model of Functional Dyspepsia

Background: Insula represents an important site in the brain for multi-modal convergence and has been implicated in processing of visceral sensation. Earlier fMRI studies in humans (Lawall, et al. Am J Physiol 2008;294:G787-94) have shown activation and sensitization of insula in response to esophageal acid stimulation. However, response characteristics of insular neurons to esophageal chemical and mechanical stimulation have not been studied. Aims: Our aims in this study were: (i) to determine the influence of esophageal acid stimulation on the insular cortex neurons (ICNs) and (ii) to characterize the responses of these neurons to esophageal distension (ED) and colorectal distension (CRD) before and after esophageal acid exposure. Methods: Eleven male rats (SD, 300-400g) were initially anaesthetized with a mixture of α-chloralose (80mg/kg, i.p.) + urethane (800mg/kg, i.p.). The anesthetics were periodically supplemented (i.v.) every 3 hours with one-fourth of the initial dose and the blood pressure was constantly monitored. A craniotomy (Bregma: +2.5 to -2.5 mm, 2.0 to 7.0 mm lateral) was performed to access insular cortex (IC). Extracellular recordings from the ICNs (Bregma: +1.8 to -2.2 mm, 5.0 to 7.4 mm lateral, 5.8 to 7.8 mm dorso-ventral) were made from the neurons that responded to ED (30-60 mmHg) and/or CRD (30-60 mmHg). After characterization of ICNs to visceral stimulation (ED and CRD), 0.1 ml of PBS (0.1M, pH 7.4) was infused slowly (0.1ml/min) into the esophagus followed by the same volume of 0.1N HCl (pH 1.2). The infusate (0.1 ml) was applied three times at 60s, 300s and 540s. The interval of each infusion time was 4 minutes. The ED and CRD were repeated 15 minutes after acid infusion to study the responses of neurons. Results: Fifteen ED or CRD sensitive neurons were studied for their responses to PBS and acid infusion. All neurons (15/15, 100%) exhibited excitation (p<0.05) following acid infusion, whereas PBS had no effect on the responses of these neurons. Eleven EDand 10 CRDresponsive neurons were fully characterized to preand post-acid condition. Following acid infusion, 11/11 (100%) ED-responsive neurons exhibited increased activity in response to ED. In contrast, 10/10 (100%) CRD-responsive neurons exhibited decreased activity during CRD. In addition, acid, but not PBS, infusion increased the spontaneous firing of all recorded neurons and continued for 30 to 45 minutes after cessation of infusion. Conclusions: Intraesophageal acid infusion significantly alters the response characteristics of ICNs in rats. Esophageal acid infusion differentially modulates the activities of ICNs that receive convergent input from esophagus and colon.

Su1972 Characterization of a Rodent Model for Functional MRI Studies of Esophageal Acid Related Sensory Physiology

Background: Insula represents an important site in the brain for multi-modal convergence and has been implicated in processing of visceral sensation. Earlier fMRI studies in humans (Lawall, et al. Am J Physiol 2008;294:G787-94) have shown activation and sensitization of insula in response to esophageal acid stimulation. However, response characteristics of insular neurons to esophageal chemical and mechanical stimulation have not been studied. Aims: Our aims in this study were: (i) to determine the influence of esophageal acid stimulation on the insular cortex neurons (ICNs) and (ii) to characterize the responses of these neurons to esophageal distension (ED) and colorectal distension (CRD) before and after esophageal acid exposure. Methods: Eleven male rats (SD, 300-400g) were initially anaesthetized with a mixture of α-chloralose (80mg/kg, i.p.) + urethane (800mg/kg, i.p.). The anesthetics were periodically supplemented (i.v.) every 3 hours with one-fourth of the initial dose and the blood pressure was constantly monitored. A craniotomy (Bregma: +2.5 to -2.5 mm, 2.0 to 7.0 mm lateral) was performed to access insular cortex (IC). Extracellular recordings from the ICNs (Bregma: +1.8 to -2.2 mm, 5.0 to 7.4 mm lateral, 5.8 to 7.8 mm dorso-ventral) were made from the neurons that responded to ED (30-60 mmHg) and/or CRD (30-60 mmHg). After characterization of ICNs to visceral stimulation (ED and CRD), 0.1 ml of PBS (0.1M, pH 7.4) was infused slowly (0.1ml/min) into the esophagus followed by the same volume of 0.1N HCl (pH 1.2). The infusate (0.1 ml) was applied three times at 60s, 300s and 540s. The interval of each infusion time was 4 minutes. The ED and CRD were repeated 15 minutes after acid infusion to study the responses of neurons. Results: Fifteen ED or CRD sensitive neurons were studied for their responses to PBS and acid infusion. All neurons (15/15, 100%) exhibited excitation (p<0.05) following acid infusion, whereas PBS had no effect on the responses of these neurons. Eleven EDand 10 CRDresponsive neurons were fully characterized to preand post-acid condition. Following acid infusion, 11/11 (100%) ED-responsive neurons exhibited increased activity in response to ED. In contrast, 10/10 (100%) CRD-responsive neurons exhibited decreased activity during CRD. In addition, acid, but not PBS, infusion increased the spontaneous firing of all recorded neurons and continued for 30 to 45 minutes after cessation of infusion. Conclusions: Intraesophageal acid infusion significantly alters the response characteristics of ICNs in rats. Esophageal acid infusion differentially modulates the activities of ICNs that receive convergent input from esophagus and colon.

Disinhibited feedback as a cause of synesthesia: Evidence from a functional connectivity study on auditory-visual synesthetes

In synesthesia, certain stimuli to one sensory modality lead to sensory perception in another unstimulated modality. In addition to other models, a two-stage model is discussed to explain this phenomenon, which combines two previously formulated hypotheses regarding synesthesia: direct cross-activation and hyperbinding. The direct cross-activation model postulates that direct connections between sensory-specific areas are responsible for co-activation and synesthetic perception. The hyperbinding hypothesis suggests that the inducing stimulus and the synesthetic sensation are coupled by a sensory nexus area, which may be located in the parietal cortex. This latter hypothesis is compatible with the disinhibited feedback model, which suggests unusual feedback from multimodal convergence areas as the cause of synesthesia. In this study, the relevance of these models was tested in a group (n=14) of auditory-visual synesthetes by performing a functional connectivity analysis on functional magnetic resonance imaging (fMRI) data. Different simple and complex sounds were used as stimuli, and functionally defined seed areas in the bilateral auditory cortex (AC) and the left inferior parietal cortex (IPC) were used for the connectivity calculations. We found no differences in the connectivity of the AC and the visual areas between synesthetes and controls. The main finding of the study was stronger connectivity of the left IPC with the left primary auditory and right primary visual cortex in the group of auditory-visual synesthetes. The results support the model of disinhibited feedback as a cause of synesthetic perception but do not suggest direct cross-activation.

Goodbye to Edward G. (Ted) Jones, MD, DPhil, 1939‐2011

Goodbye to Edward G. (Ted) Jones, MD, DPhil, 1939‐2011

Novel claustrum activation observed during a visuomotor adaptation task using a viewing window paradigm

Previous literature has reported a wide range of anatomical correlates when participants are required to perform a visuomotor adaptation task. However, traditional adaptation tasks suffer a number of inherent limitations that may, in part, give rise to this variability. For instance, the sparse visual environment does not map well onto conditions in which a visuomotor transformation would normally be required in everyday life. To further clarify these neural underpinnings, functional magnetic resonance imaging (fMRI) was performed on 17 (6M, age range 20–45 years old; mean age = 26) naive participants performing a viewing window task in which a visuomotor transformation was created by varying the relationship between the participant's movement and the resultant movement of the viewing window. The viewing window task more naturally replicates scenarios in which haptic and visual information would be combined to achieve a higher-level goal. Even though activity related to visuomotor adaptation was found within previously reported regions of the parietal lobes, frontal lobes, and occipital lobes, novel activation patterns were observed within the claustrum – a region well-established as multi-modal convergence zone. These results confirm the diversity in the number and location of neurological systems recruited to perform a required visuomotor adaptation, and provide the first evidence of participation of the claustrum to overcome a visuomotor transformation.

Smelling Sounds: Olfactory–Auditory Sensory Convergence in the Olfactory Tubercle

Historical and psychophysical literature has demonstrated a perceptual interplay between olfactory and auditory stimuli-the neural mechanisms of which are not understood. Here, we report novel findings revealing that the early olfactory code is subjected to auditory cross-modal influences. In vivo extracellular recordings from the olfactory tubercle, a trilaminar structure within the basal forebrain, of anesthetized mice revealed that olfactory tubercle single units selectively respond to odors-with 65% of units showing significant odor-evoked activity. Remarkably, 19% of olfactory tubercle single units also showed robust responses to an auditory tone. Furthermore, 29% of single units tested displayed supraadditive or suppressive responses to the simultaneous presentation of odor and tone, suggesting cross-modal modulation. In contrast, olfactory bulb units did not show significant responses to tone presentation nor modulation of odor-evoked activity by tone-suggesting a lack of olfactory-auditory convergence upstream from the olfactory tubercle. Thus, the tubercle presents itself as a source for direct multimodal convergence within an early stage of odor processing and may serve as a seat for psychophysical interactions between smells and sounds.

Interaction of sound and sight during action perception: Evidence for shared modality-dependent action representations

Seeing or hearing manual actions activates the mirror neuron system, i.e., specialized neurons within motor areas which fire not only when an action is performed but also when it is passively perceived. Although it has been shown that mirror neurons respond to either action-specific vision or sound, it remains a topic of debate whether and how vision and sound interact during action perception. Here we used transcranial magnetic stimulation to explore multimodal interactions in the human motor system, namely at the level of the primary motor cortex (M1). Corticomotor excitability in M1 was measured while subjects perceived unimodal visual (V), unimodal auditory (A), or multimodal (V+A) stimuli of a simple hand action. In addition, incongruent multimodal stimuli were included, in which incongruent vision or sound was presented simultaneously with the auditory or visual action stimulus. A selective response increase was observed to the congruent multimodal stimulus as compared to the unimodal and incongruent multimodal stimuli. These findings speak in favour of 'shared' action representations in the human motor system that are evoked in a 'modality-dependent' way, i.e., they are elicited most robustly by the simultaneous presentation of congruent auditory and visual stimuli. Multimodality in the perception of hand movements bears functional similarities to speech perception, suggesting that multimodal convergence is a generic feature of the mirror system which applies to action perception in general.

Perceptual Systems Controlling Speech Production

It is proposed that the acquisition and maintenance of fluent speech depend on the rapid temporal integration of motor feedforward and polysensory (auditory and somatosensory) feedback signals. In a functional magnetic resonance imaging study on 21 healthy right-handed, English-speaking volunteers, we investigated activity within these motor and sensory pathways and their integration during speech. Four motor conditions were studied: two speech conditions (propositional and nonpropositional speech) and two silent conditions requiring repetitive movement of the principal articulators (jaw and tongue movements). The scanning technique was adapted to minimize artifact associated with overt speech production. Our result indicates that this multimodal convergence occurs within the left and right supratemporal planes (STPs), with peaks of activity at their posteromedial extents, in regions classically considered as unimodal auditory association cortex. This cortical specialization contrasted sharply with the response of somatosensory association cortex (SII), in which activity was suppressed during speech but not during the silent repetitive movement of the principal articulators. It was also clearly distinct from the response of lateral auditory association cortex, which responded to auditory feedback alone, and from that within a left lateralized ventrolateral temporal and inferior frontal system, which served lexical- and sentence-level language retrieval. This response of cortical regions related to speech production is not predicted by the classical model of hierarchical cortical processing, providing new insights into the role of the STP in polysensory integration and into the modulation of activity in SII during normal speech production. These findings have novel implications for the acquisition and maintenance of fluent speech.

Altered oscillatory brain dynamics after repeated traumatic stress

BackgroundRepeated traumatic experiences, e.g. torture and war, lead to functional and structural cerebral changes, which should be detectable in cortical dynamics. Abnormal slow waves produced within circumscribed brain regions during a resting state have been associated with lesioned neural circuitry in neurological disorders and more recently also in mental illness.MethodsUsing magnetoencephalographic (MEG-based) source imaging, we mapped abnormal distributions of generators of slow waves in 97 survivors of torture and war with posttraumatic stress disorder (PTSD) in comparison to 97 controls.ResultsPTSD patients showed elevated production of focally generated slow waves (1–4 Hz), particularly in left temporal brain regions, with peak activities in the region of the insula. Furthermore, differential slow wave activity in right frontal areas was found in PTSD patients compared to controls.ConclusionThe insula, as a site of multimodal convergence, could play a key role in understanding the pathophysiology of PTSD, possibly accounting for what has been called posttraumatic alexithymia, i.e., reduced ability to identify, express and regulate emotional responses to reminders of traumatic events. Differences in activity in right frontal areas may indicate a dysfunctional PFC, which may lead to diminished extinction of conditioned fear and reduced inhibition of the amygdala.