Bihemispheric network dynamics coordinating vocal feedback control.

Repeated episodes of hypoxia, hypercapnia and transient blood pressure elevation in obstructive sleep apnea syndrome (OSAS) may damage neutral structures and induce cerebral metabolic impairment. This study aimed to determine the impact of OSAS on cerebral metabolites measured by (1)H magnetic resonance spectroscopy ((1)H -MRS). Twenty OSAS patients underwent standard overnight polysomnography and (1)H-MRS separately. Proton volumes of interest (VOIs) were placed in frontal and midtemporal regions bilaterally. Significantly lower values of the N-acetylaspartate (NAA)/creatine (Cr) ratio were found in frontal regions (P < 0.004) compared with 20 age-matched control subjects. A significant increase in the myo-inositol (Ins)/Cr ratio was evident bilaterally in temporal and frontal regions (P < 0.00002 and P < 0.04). Choline (Cho)/Cr ratio values were also significantly greater in temporal regions (P < 0.00001). A significant negative correlation (r = -0.51, P < 0.03) was found between the apnea-hypopnea index (AHI) and NAA/Cr ratio in the frontal regions of OSAS patients. Reduction in the NAA/Cr ratio in frontal regions of OSAS patients could be related to neural loss. Increase in the Cho/Cr ratio in temporal regions and Ins/Cr ratio in both frontal and temporal regions could be interpreted as evidence of membrane breakdown and reactive gliosis, respectively, consequent to repeated episodes of hypoxia in OSAS.

Across the animal kingdom, neural responses in the auditory cortex are suppressed during vocalization, and humans are no exception. A common hypothesis is that suppression increases sensitivity to auditory feedback, enabling the detection of vocalization errors. This hypothesis has been previously confirmed in non-human primates, however a direct link between auditory suppression and sensitivity in human speech monitoring remains elusive. To address this issue, we obtained intracranial electroencephalography (iEEG) recordings from 35 neurosurgical participants during speech production. We first characterized the detailed topography of auditory suppression, which varied across superior temporal gyrus (STG). Next, we performed a delayed auditory feedback (DAF) task to determine whether the suppressed sites were also sensitive to auditory feedback alterations. Indeed, overlapping sites showed enhanced responses to feedback, indicating sensitivity. Importantly, there was a strong correlation between the degree of auditory suppression and feedback sensitivity, suggesting suppression might be a key mechanism that underlies speech monitoring. Further, we found that when participants produced speech with simultaneous auditory feedback, posterior STG was selectively activated if participants were engaged in a DAF paradigm, suggesting that increased attentional load can modulate auditory feedback sensitivity.

The Hayling Sentence Completion Task (HSCT) is known to activate left hemisphere frontal and temporal language regions. However, the effective connectivity between frontal and temporal language regions associated with the task has yet to be examined. The aims of the study were to examine activation and effective connectivity during the HSCT using a functional magnetic resonance imaging (fMRI) paradigm in which participants made overt verbal responses. We predicted that producing an incongruent response (response suppression), compared to a congruent one (response initiation), would be associated with greater activation in the left prefrontal cortex and an increase in the effective connectivity between temporal and frontal regions. Fifteen participants were scanned while completing 80 sentence stems. The congruency and constraint of sentences varied across trials. Dynamic Causal Modeling (DCM) and Bayesian Model Selection (BMS) were used to compare a set of alternative DCMs of fronto-temporal connectivity. The HSCT activated regions in the left temporal and prefrontal cortices, and the cuneus. Response suppression was associated with greater activation in the left middle and orbital frontal gyri and the bilateral precuneus than response initiation. Left middle temporal and frontal regions identified by the conventional fMRI analyses were entered into the DCM analysis. Using a systematic BMS procedure, the optimal DCM showed that the connection from the left middle temporal gyrus, which was driven by verbal stimuli per se, was significantly increased in strength during response suppression compared to initiation. Greater effective connectivity between left temporal and prefrontal regions during response suppression may reflect the transfer of information from posterior temporal regions where semantic and lexical information is stored to prefrontal regions where it is manipulated in preparation for an appropriate response.

Introduction: Diabetes mellitus (DM) is a chronic disease associated with cognitive decline and dementia in the elderly population. This exploratory study analysed the brain wave changes during cognitive task performance in working adults with and without type 2 diabetes mellitus (T2DM). MATERIALS AND Methods: The Mini-Mental State Examination was used to screen subject’s cognitive function and quantitative electroencephalography was used to analyse subject’s brain waves at rest and whilst performing the serial seven test. Results: When performing the serial seven test, the diabetic group showed a higher absolute power of theta waves in the left frontal (Fp1, 16.22 ± 3.81 vs 3.75 ± 1.69; p = 0.022) and temporal regions (T3, 24.27 ± 3.69 vs 7.92 ± 2.17; p = 0.045), but lower absolute power of beta waves in both the frontal regions (Fp1, 27.35 ± 3.67 vs 41.14 ± 5.67; p = 0.029; Fp2, 23.01 ± 3.31 vs 39.05 ± 2.64; p = 0.041) and left temporal region (T3, 37.93 ± 4.64 vs 50.94 ± 3.56; p = 0.046) when compared to those of the control group. The diabetic group took longer to complete the task (127.9 ± 8.3 s vs 95.6 ± 5.9 s; p = 0.032) than the control group, despite no statistically significant difference in correct response rates. Diabetes duration was positively correlated with the theta/alpha ratio in the left frontal (Fp1, r = 0.525; p = 0.041) and temporal (T3, r = 0.618; p = 0.037) regions. Conclusions: T2DM may affect cognitive function in patients before clinical manifestation.

ERP correlates of language-specific processing of auditory pitch feedback during self-vocalization

Infants often pay special attention to speech sounds, and they appear to detect key features of these sounds. To investigate the neural foundation of speech perception in infants, we measured cortical activation using near‐infrared spectroscopy. We presented the following three types of auditory stimuli while 3‐month‐old infants watched a silent movie: (1) normal speech sounds; (2) sine wave speech (SWS) sounds consisting of three sine waves that tracked the first, second, and third formants of speech sounds; and (3) synthesized tones composed of three pure tones. Statistical analyses of oxygenated hemoglobin (oxy‐Hb) signals revealed significant activation in the left and right auditory areas in all conditions. Direct comparisons of oxy‐Hb signal changes between SWS and synthesized tones showed significant differences in the left frontal and temporal regions. Furthermore, comparisons of oxy‐Hb signal changes between speech sounds and SWS exhibited significant differences in a left posterior temporal region. These results demonstrated that functional differentiation occurs in the left temporal cortex while infants perceive different types of auditory information. Coactivation of the left temporal and frontal regions by speech sounds suggests the initial formation of a left fronto‐temporal network related to infant speech processing. Clarification of the functional role of this left‐lateralized network will help understand the speech code.

Speech production involves a combination of feedforward and sensory feedback-based control mechanisms. The latter have been characterized in experiments involving real-time perturbations during speech. Unexpected perturbations of auditory feedback result in corrective motor responses with a minimum latency of approximately 100 ms after perturbation onset. These responses have been shown for both pitch and formant frequency perturbations, and the responsible neural circuitry includes portions of the superior temporal gyrus and ventral premotor cortex (vPMC). Corrective responses to somatosensory perturbations (such as a downward force applied to the jaw) occur approximately 50 ms after perturbation onset and are mediated by ventral somatosensory cortex and vPMC. The degree to which an individual weights auditory versus somatosensory feedback varies substantially. Such differences rely in part on differences in sensory acuity, e.g., a speaker with relatively poor hearing is likely to rely more heavily on somatosensory feedback control mechanisms than auditory feedback control mechanisms. Additionally, reliance on feedback control may be modulated to compensate for impairments in the feedforward system for speech, e.g., adults who stutter show a reduced reliance on auditory feedback control compared to fluent speakers, perhaps because auditory feedback can have a deleterious effect on speech initiation in stuttering.

Depression is one of the most common psychiatric illnesses. Its influence on brain perfusion has been demonstrated, but conflicting data exist on follow-up after drug treatment. The aim of our study was to evaluate the effects of antidepressant drugs on regional cerebral blood flow (rCBF) in patients with depression after 3 weeks and 6 months of drug therapy. Clinical criteria for depression without psychosis were met according to psychiatric evaluation. Severity of depression was evaluated with the Hamilton Depression Rating Scale (HAMD) before every scintigraphic study. rCBF was assessed using technetium-99m bicisate (Neurolite) brain single-photon emission tomography in nine patients with severe depression before the beginning of antidepressant drug therapy and 3 weeks and six months after initiation of therapy. Only patients with no change in antidepressant medication during the study were included. No antipsychotic drugs were used. Cerebellum was used as the reference region. rCBF was evaluated for eight regions in each study in three consecutive transversal slices. Follow-up studies were compared with the baseline study. The mean HAMD score was 25.5 points initially, 16 at the second examination and 8.8 after 6 months. Global CBF was decreased compared with the reference region in drug-free patients. Perfusion of left frontal and temporal regions was significantly lower (P < 0.005) in comparison with the contralateral side. After therapy, a moderate decrease in perfusion was seen in the right frontal region (P < 0.05). Perfusion decreased further after 6 months in the right frontal (P < 0.005) and temporal regions (P < 0.01). The highly significant asymmetry in perfusion between the left and right frontal and temporal lobes almost disappeared during treatment. Our findings implicate dysfunction of the frontal and temporal cortex in clinically depressed patients before specific drug treatment. Clinical improvement and decreases in HAMD score after 3 weeks and after 6 months reflect the treatment effect on mood-related rCBF changes.

Brain regions are not independent. They are interconnected by white matter tracts, together forming one integrative complex network. The topology of this network is crucial for efficient information integration between brain regions. Here, we demonstrate that schizophrenia involves an aberrant topology of the structural infrastructure of the brain network. Using graph theoretical analysis, complex structural brain networks of 40 schizophrenia patients and 40 human healthy controls were examined. Diffusion tensor imaging was used to reconstruct the white matter connections of the brain network, with the strength of the connections defined as the level of myelination of the tracts as measured through means of magnetization transfer ratio magnetic resonance imaging. Patients displayed a preserved overall small-world network organization, but focusing on specific brain regions and their capacity to communicate with other regions of the brain revealed significantly longer node-specific path lengths (higher L) of frontal and temporal regions, especially of bilateral inferior/superior frontal cortex and temporal pole regions. These findings suggest that schizophrenia impacts global network connectivity of frontal and temporal brain regions. Furthermore, frontal hubs of patients showed a significant reduction of betweenness centrality, suggesting a less central hub role of these regions in the overall network structure. Together, our findings suggest that schizophrenia patients have a less strongly globally integrated structural brain network with a reduced central role for key frontal hubs, resulting in a limited structural capacity to integrate information across brain regions.

Zebra finches memorize a tutor song as juveniles, and then faithfully reproduce this song for the remainder of their lives. This thesis investigates how the intricate and concerted activity of ensembles of neurons in the zebra finch brain gives rise to this complex behavior. The first section of the thesis demonstrates how neurons in RA, a pre-motor song control nucleus, coordinate their activity to generate the instantaneous spectral and temporal structure seen in the song. Similar sounds are produced by entirely different ensembles of RA neurons. Additionally, rapidly changing patterns of RA neural activity are capable of generating constant acoustic outputs. This is a new form of neural coding, previously unobserved in any other system. This unusual neural representation provides a concise account of an unexplained aspect of song learning. The second part of the thesis develops a new, noninvasive method of altering the auditory feedback heard by singing zebra finches. This type of feedback perturbation causes the normally stable songs of adult birds to deteriorate, indicating that auditory feedback is essential to song control throughout life. Restoration of the normal auditory feedback heard by these birds enables the gradual recovery of their original songs, demonstrating that a memory of the original song persists in the song control system despite the destabilization of the behavior. The song is thus maintained by an active feedback control process. The final project investigates the role of nucleus LMAN in real-time song control via auditory feedback. Neurons in nucleus LMAN were previously believed to compare auditory feedback to a memorized song template. The result of this comparison was thought to be used as an error-correction signal to update the motor control program. By recording from individual LMAN neurons while simultaneously manipulating the auditory feedback heard by the singing bird, it is shown that during singing, rather than auditory feedback, LMAN processes an efference copy of the motor commands used to generate the bird's song. This suggests a different model of the system, in which the efference copy is the basis of the real-time error-correction signal. Taken together, these three projects significantly expand our knowledge of the neural mechanisms responsible for the generation of birdsong.

Understanding the evolution of regional and hemispheric asymmetries in the early stages of life is essential to the advancement of developmental neuroscience. By using 2 noninvasive optical methods, frequency-domain near-infrared spectroscopy and diffuse correlation spectroscopy, we measured cerebral hemoglobin oxygenation (SO(2)), blood volume (CBV), an index of cerebral blood flow (CBF(i)), and the metabolic rate of oxygen (CMRO(2i)) in the frontal, temporal, and parietal regions of 70 premature and term newborns. In concordance with results obtained using more invasive imaging modalities, we verified both hemodynamic (CBV, CBF(i), and SO(2)) and metabolic (CMRO(2i)) parameters were greater in the temporal and parietal regions than in the frontal region and that these differences increased with age. In addition, we found that most parameters were significantly greater in the right hemisphere than in the left. Finally, in comparing age-matched males and females, we found that males had higher CBF(i) in most cortical regions, higher CMRO(2i) in the frontal region, and more prominent right-left CBF(i) asymmetry. These results reveal, for the first time, that we can detect regional and hemispheric asymmetries in newborns using noninvasive optical techniques. Such a bedside screening tool may facilitate early detection of abnormalities and delays in maturation of specific cortical areas.

The Lateral Asymmetry of the Human Brain Studied by Volumetric Magnetic Resonance Imaging

The Lateral Asymmetry of the Human Brain Studied by Volumetric Magnetic Resonance Imaging

Vocal control plays a critical role in smooth social communication. Speakers constantly monitor auditory feedback (AF) and make adjustments when their voices deviate from their intentions. Previous studies have shown that when certain acoustic features of the AF are artificially altered, speakers compensate for this alteration in the opposite direction. However, little is known about how the vocal control system implements compensations for alterations of different acoustic features, and associates them with subjective consciousness. The present study investigated whether compensations for the fundamental frequency (F0), which corresponds to perceived pitch, and formants, which contribute to perceived timbre, can be performed unconsciously and independently. Forty native Japanese speakers received two types of altered AF during vowel production that involved shifts of either only the formant frequencies (formant modification; Fm) or both the pitch and formant frequencies (pitch + formant modification; PFm). For each type, three levels of shift (slight, medium, and severe) in both directions (increase or decrease) were used. After the experiment, participants were tested for whether they had perceived a change in the F0 and/or formants. The results showed that (i) only formants were compensated for in the Fm condition, while both the F0 and formants were compensated for in the PFm condition; (ii) the F0 compensation exhibited greater precision than the formant compensation in PFm; and (iii) compensation occurred even when participants misperceived or could not explicitly perceive the alteration in AF. These findings indicate that non-experts can compensate for both formant and F0 modifications in the AF during vocal production, even when the modifications are not explicitly or correctly perceived, which provides further evidence for a dissociation between conscious perception and action in vocal control. We propose that such unconscious control of voice production may enhance rapid adaptation to changing speech environments and facilitate mutual communication.

Technological tools, like electroencephalography and functional near-infrared spectroscopy, have deepened our understanding of cortical regions involved in balance control. In this systematic literature review, we aimed to identify the prevalent cortical areas activated during balance tasks with specific motor or cognitive demands. Our search strategy encompassed terms related to balance control and cortical activity, yielding 2250 results across five databases. After screening, 67 relevant articles were included in the review. Results indicated that manipulations of visual and/or somatosensory information led to prevalent activity in the parietal, frontal and temporal regions; manipulations of the support base led to prevalent activity of the parietal and frontal regions; both balance-cognitive dual-tasking and reactive responses to extrinsic perturbations led to prevalent activity in the frontal and central regions. These findings deepen our comprehension of the cortical regions activated to manage the complex demands of maintaining body balance in the performance of tasks posing specific requirements. By understanding these cortical activation patterns, researchers and clinicians can develop targeted interventions for balance-related disorders.