The Functional Neuroanatomy of Lexical Tone Perception: An Activation Likelihood Estimation Meta-Analysis

In tonal language such as Chinese, lexical tone serves as a phonemic feature in determining word meaning. Meanwhile, it is close to prosody in terms of suprasegmental pitch variations and larynx-based articulation. The important yet mixed nature of lexical tone has evoked considerable studies, but no consensus has been reached on its functional neuroanatomy. This meta-analysis aimed at uncovering the neural network of lexical tone perception in comparison with that of phoneme and prosody in a unified framework. Independent Activation Likelihood Estimation meta-analyses were conducted for different linguistic elements: lexical tone by native tonal language speakers, lexical tone by non-tonal language speakers, phoneme, word-level prosody, and sentence-level prosody. Results showed that lexical tone and prosody studies demonstrated more extensive activations in the right than the left auditory cortex, whereas the opposite pattern was found for phoneme studies. Only tonal language speakers consistently recruited the left anterior superior temporal gyrus (STG) for processing lexical tone, an area implicated in phoneme processing and word-form recognition. Moreover, an anterior-lateral to posterior-medial gradient of activation as a function of element timescale was revealed in the right STG, in which the activation for lexical tone lied between that for phoneme and that for prosody. Another topological pattern was shown on the left precentral gyrus (preCG), with the activation for lexical tone overlapped with that for prosody but ventral to that for phoneme. These findings provide evidence that the neural network for lexical tone perception is hybrid with those for phoneme and prosody. That is, resembling prosody, lexical tone perception, regardless of language experience, involved right auditory cortex, with activation localized between sites engaged by phonemic and prosodic processing, suggesting a hierarchical organization of representations in the right auditory cortex. For tonal language speakers, lexical tone additionally engaged the left STG lexical mapping network, consistent with the phonemic representation. Similarly, when processing lexical tone, only tonal language speakers engaged the left preCG site implicated in prosody perception, consistent with tonal language speakers having stronger articulatory representations for lexical tone in the laryngeal sensorimotor network. A dynamic dual-stream model for lexical tone perception was proposed and discussed

Psychoses, language and brain asymmetry: fMRI connectivity alterations in bipolar disorders.

INTRODUCTION A mood characterised by alternating mania and depression have been matter of curiosity and attention since ancient times. According to T.J. Crow’s theory on psychosis, Schizophrenia is strictly linked to the development of the faculty of language (begun in hominids from 6 to 4.2 million years ago) which depends by (anatomical and functional) asymmetry observable between the two cerebral hemispheres (Crow 2004). Several data in the recent (and older) (Griesinger 1845) scientific literature support the hypothesis that schizophrenia and bipolar disorder are similar due to a large number of partially common features: symptomatology, genetics, cognitive features, neurobiology, connectivity alteration, etc.. A brief historical account about how often the classification of this disease changed across the last two centuries may suggest how the knowledge underling this diagnostic category is still fragile. AIM OF THE RESEARCH The goal of this paper is to study Functional Connectivity (FC) among bipolar patients and to test the compatibility of Crow’s paradigm with Bipolar Disorder, verifying the potential presence of hemispheric asymmetry alteration (left dominance deficit) through fMRI analysis. MATERIALS AND METHODS 18 outpatients of the Mood Disorders Unit at the Psychiatric Clinic of the University of Padua have been recruited. All subjects had a diagnosis of Bipolar Disorder type I or type II, according to the criteria of the DSM-IV-TR). 16 healthy individuals were chosen matched for age, sex and education. Clinical and psychological conditions at the time of the experiment were investigated through some psychometric scales widely used for the evaluation of mood, anxiety and other psychopathologic aspects. All subjects underwent a MRI scan both in resting state and while they were attending two tasks: a phonemic (verbal fluency) exercise and a visuo-spatial test (mental rotations). RESULTS From the neuropsychological point of view the phonemic task revealed no significant (p<0.05) differences between groups; on the contrary patients group showed decreased performance at the visuo-spatial task. MRI FC was analysed using two different techniques. Independent Component Analysis (ICA) showed mainly a volume within the Dorsal Attention Network located in left Precuneus (Brodmann Area 7) where patient group presented a reduction of FC compared to controls. Graph analysis brought to light a number of inter-hemispheric and left intra-hemispheric connections revealed to be significantly less active in patients compared to controls, on the contrary substantial conservation of indices at the Network Level was observed

Neuroanatomical and perceptual deficits in auditory agnosia : a study of an auditory agnosia patient with inferior colliculus damage

Auditory agnosia is a rare disorder in which individuals lose the ability to understand sounds. In this thesis, I examine an auditory agnosia patient with brainstem damage, but intact cortex. The patient was severely impaired when instructed to type the names of sounds. The patient, however, was only mildly impaired when instructed to choose the correct sound out of four written alternatives, which implies partial auditory perception. In two fMRI scans, conducted a year apart, passive listening to sounds resulted with a unique activation pattern in her auditory cortices. In particular, her anterior primary and associative auditory fields were much less responsive to sounds than more posterior primary and associative auditory fields. The functional dissociation between these regions suggests connections between the anterior primary and associative regions, and between the posterior primary and associative regions. Hitherto, these connections were only reported in monkeys. An EEG study that examined mismatch negativity for frequency, duration, and intensity of sounds, demonstrated that the patient’s ability of detecting changes to frequency and duration of sounds is bilaterally impaired, whereas the detection of changes to sound’s intensity is impaired in the left hemisphere but intact in the right hemisphere. Behavioral studies also show that the patient’s auditory perceptual deficit is partially due to impaired perception of the duration of sounds. For instance, when the patient heard two subsequent clicks, she was impaired at discriminating these sounds by the duration of their intervening interval. In a spoken word discrimination task, she was also impaired at discriminating words that could only be distinguished by their temporal properties (voice onset-time). Based on these findings, I argue that the patient experiences auditory agnosia be- cause the brain stem injury prevents the transmission of critical auditory information to the auditory cortex. As a result of this absence, the auditory fields responsible for sound recognition, the anterior auditory fields, are not recruited. In a dichotic listening task, the patient extinguished sounds presented to the right ear, and in a sound localization task she perceived sounds as emerging from the left auditory hemi-field. Given cumulative evidence that associates the posterior auditory cortex with sound localization and phonological-acoustic analysis of verbal material from the contra-lateral hemi-field, the patient’s performance in these tasks suggest that her spared auditory abilities is due to processing in her right posterior auditory cortex. This role of the patient’s right posterior auditory cortex is consistent with both the fMRI study, in which the right posterior auditory cortex was consistently responsive to sounds, and the EEG study, in which detection of changes to sound intensity was restricted to the right hemisphere

Neurophysiological assessments of low-level and high-level interdependencies between auditory and visual systems in the human brain

This dissertation investigates the functional interplay between visual and auditory systems and its degree of experience-dependent plasticity. To function efficiently in everyday life, we must rely on our senses, building complex hierarchical representations about the environment. Early sensory deprivation, congenital (from birth) or within the first year of life, is a key model to study sensory experience and the degree of compensatory reorganizations (i.e., neuroplasticity). Neuroplasticity can be intramodal (within the sensory system) and crossmodal (the recruitment of deprived cortical areas for remaining senses). However, the exact role of early sensory experience and the mechanisms guiding experience-driven plasticity need further investigation. To this aim, we performed three electroencephalographic studies, considering the aspects: 1) sensory modality (auditory/visual), 2) hierarchy of the brain functional organization (low-/high-level), and 3)sensory deprivation (deprived/non-deprived cortices). The first study explored how early auditory experience affects low-level visual processing, using time-frequency analysis on the data of early deaf individuals and their hearing counterparts. The second study investigated experience- dependent plasticity in hierarchically organized face processing, applying fast periodic visual stimulation in congenitally deaf signers and their hearing controls. The third study assessed neural responses of blindfolded participants, using naturalistic stimuli together with temporal response function, and evaluated neural tracking in hierarchically organized speech processing when retinal input is absent, focusing on the role of the visual cortex. The results demonstrate the importance of atypical early sensory experience in shaping (via intra-and crossmodal changes) the brain organization at various hierarchical stages of sensory processing but also support the idea that some crossmodal effects emerge even with typical experience. This dissertation provides new insights into understanding the functional interplay between visual and auditory systems and the related mechanisms driving experience-dependent plasticity and may contribute to the development of sensory restoration tools and rehabilitation strategies for sensory-typical and sensory-deprived populations

The anterior pathway for intelligible speech: insights from univariate and multivariate methods

Whilst there is broad agreement concerning the existence of an anterior processing stream in the human brain concerned with extracting meaning from speech, there is an ongoing controversy as to whether intelligible speech is first resolved in left anterior or bilateral posterior temporal fields (Hickok and Poeppel, 2007;Rauschecker and Scott, 2009). Proponents of the bilateral processing model argue that bilateral responses are driven by the acoustic properties of the speech signal, whilst proponents of the left lateralised model suggest that left lateralisation is driven by access to linguistic representations. This thesis directly addresses these controversies using Functional Magnetic Resonance Imaging (fMRI) and univariate and multivariate analysis methods. Two main questions are addressed: (1) where are responses to intelligible, and intelligible but degraded speech, separated from responses to acoustic complexity and (2) does the resulting pattern of lateralisation, or otherwise, derive from the acoustic properties or the linguistic status of speech. The results of this thesis reconcile, to some degree, the two theoretical positions. I show that the most consistent and largest amplitude responses to intelligible, and degraded but intelligible speech, are found in the left anterior Superior Temporal Sulcus (STS). Additional responses were also found in right anterior and left posterior STS, however, these were less consistently identified. Regions of the left posterior STS showed sensitivity to resolved intelligible speech and also showed a response likely to reflect acoustic-phonetic processing supporting the resolving of intelligibility. Right posterior STS responses to intelligible speech were noticeably absent across all studies. No evidence was found for a relative acoustic basis for hemispheric lateralisation in the case of speech derived manipulations of spectrum and amplitude, but evidence was found in support of a left hemisphere specialism for resolving intelligible speech, supporting a relative left lateralisation to speech driven by linguistic rather than acoustic factors