Phonological Feature Repetition Suppression in the Left Inferior Frontal Gyrus

Processing of auditory feedback in perisylvian and insular cortex

When we speak, we not only make movements with our mouth, lips, and tongue, but we also hear the sound of our own voice. Thus, speech production in the brain involves not only controlling the movements we make, but also auditory and sensory feedback. Auditory responses are typically suppressed during speech production compared to perception, but how this manifests across space and time is unclear. Here we recorded intracranial EEG in seventeen pediatric, adolescent, and adult patients with medication-resistant epilepsy who performed a reading/listening task to investigate how other auditory responses are modulated during speech production. We identified onset and sustained responses to speech in bilateral auditory cortex, with a selective suppression of onset responses during speech production. Onset responses provide a temporal landmark during speech perception that is redundant with forward prediction during speech production. Phonological feature tuning in these "onset suppression" electrodes remained stable between perception and production. Notably, the posterior insula responded at sentence onset for both perception and production, suggesting a role in multisensory integration during feedback control.

High-level language brain regions process sublexical regularities

A network of left frontal and temporal brain regions supports language processing. This "core" language network stores our knowledge of words and constructions as well as constraints on how those combine to form sentences. However, our linguistic knowledge additionally includes information about phonemes and how they combine to form phonemic clusters, syllables, and words. Are phoneme combinatorics also represented in these language regions? Across five functional magnetic resonance imaging experiments, we investigated the sensitivity of high-level language processing brain regions to sublexical linguistic regularities by examining responses to diverse nonwords-sequences of phonemes that do not constitute real words (e.g. punes, silory, flope). We establish robust responses in the language network to visually (experiment 1a, n = 605) and auditorily (experiments 1b, n = 12, and 1c, n = 13) presented nonwords. In experiment 2 (n = 16), we find stronger responses to nonwords that are more well-formed, i.e. obey the phoneme-combinatorial constraints of English. Finally, in experiment 3 (n = 14), we provide suggestive evidence that the responses in experiments 1 and 2 are not due to the activation of real words that share some phonology with the nonwords. The results suggest that sublexical regularities are stored and processed within the same fronto-temporal network that supports lexical and syntactic processes.

Speaker-induced Suppression in EEG during a Naturalistic Reading and Listening Task

Speaking elicits a suppressed neural response when compared with listening to others' speech, a phenomenon known as speaker-induced suppression (SIS). Previous research has focused on investigating SIS at constrained levels of linguistic representation, such as the individual phoneme and word level. Here, we present scalp EEG data from a dual speech perception and production task where participants read sentences aloud then listened to playback of themselves reading those sentences. Playback was separated into immediate repetition of the previous trial and randomized repetition of a former trial to investigate if forward modeling of responses during passive listening suppresses the neural response. Concurrent EMG was recorded to control for movement artifact during speech production. In line with previous research, ERP analyses at the sentence level demonstrated suppression of early auditory components of the EEG for production compared with perception. To evaluate whether linguistic abstractions (in the form of phonological feature tuning) are suppressed during speech production alongside lower-level acoustic information, we fit linear encoding models that predicted scalp EEG based on phonological features, EMG activity, and task condition. We found that phonological features were encoded similarly between production and perception. However, this similarity was only observed when controlling for movement by using the EMG response as an additional regressor. Our results suggest that SIS operates at a sensory representational level and is dissociated from higher order cognitive and linguistic processing that takes place during speech perception and production. We also detail some important considerations when analyzing EEG during continuous speech production.

Functional connectivity between parietal and temporal lobes mediates internal forward models during speech production

Internal forward models hypothesize functional links between motor and sensory systems for predicting the consequences of actions. Recently, the cascaded theory proposes that somatosensory estimation in the inferior parietal lobe (IPL) can be a relay computational structure, converting motor signals into predictions of auditory consequences in a serial processing manner during speech production. The study used fMRI with functional connectivity (FC) analyses to investigate the proposed cascaded processes using three speech tasks: overt articulation (OA), silent articulation (SA) and imagined articulation (IA). The FC results showed that connectivity between aIPL and STG was increased in OA compared with SA, suggesting that the relationship between somatosensory and auditory estimations can be modulated by speech tasks. Moreover, stronger connectivity between IFGoper and pIPL, and between pIPL and STG were observed in SA and IA compared with OA. These results are consistent with a cascaded process in the internal forward models.

Phonological and Semantic Specialization in 9- to 10-Year-Old Children During Auditory Word Processing

One of the core features of brain maturation is functional specialization. Previous research has found that 7- to 8-year-old children start to specialize in both the temporal and frontal lobes. However, as children continue to develop their phonological and semantic skills rapidly until approximately 10 years old, it remained unclear whether any changes in specialization later in childhood would be detected. Thus, the goal of the current study was to examine phonological and semantic specialization in 9- to 10-year-old children during auditory word processing. Sixty-one children were included in the analysis. They were asked to perform a sound judgment task and a meaning judgment task, each with both hard and easy conditions to examine parametric effects. Consistent with previous results from 7- to 8-year-old children, direct task comparisons revealed language specialization in both the temporal and frontal lobes in 9- to 10-year-old children. Specifically, the left dorsal inferior frontal gyrus showed greater activation for the sound than the meaning task whereas the left middle temporal gyrus showed greater activation for the meaning than the sound task. Interestingly, in contrast to the previously reported finding that 7- to 8-year-old children primarily engage a general control region during the harder condition for both tasks, we showed that 9- to 10-year-old children recruited language-specific regions to process the more difficult task conditions. Specifically, the left superior temporal gyrus showed greater activation for the phonological parametric manipulation whereas the left ventral inferior frontal gyrus showed greater activation for the semantic parametric manipulation.

Dynamics of working memory process revealed by independent component analysis in an fMRI study

Human memory is prone to errors in many everyday activities but also when cultivating hobbies such as traveling and/or learning a new language. For instance, while visiting foreign countries, people erroneously recall foreign language words that are meaningless to them. Our research simulated such errors in a modified Deese-Roediger-McDermott paradigm for short-term memory with phonologically related stimuli aimed at uncovering behavioral and neuronal indices of false memory formation with regard to time-of-day, a variable known to influence memory. Fifty-eight participants were tested in a magnetic resonance (MR) scanner twice. The results of an Independent Component Analysis revealed encoding-related activity of the medial visual network preceding correct recognition of positive probes and correct rejection of lure probes. The engagement of this network preceding false alarms was not observed. We also explored if diurnal rhythmicity influences working memory processes. Diurnal differences were seen in the default mode network and the medial visual network with lower deactivation in the evening hours. The GLM results showed greater activation of the right lingual gyrus, part of the visual cortex and the left cerebellum in the evening. The study offers new insight into the mechanisms associated with false memories, suggesting that deficient engagement of the medial visual network during the memorization phase of a task results in short-term memory distortions. The results shed new light on the dynamics of working memory processes by taking into account the effect of time-of-day on memory performance.

Start shallow and grow deep: The development of a Hebrew reading brain

Brain plasticity implies that readers of different orthographies can have different reading networks. Theoretical models suggest that reading acquisition in transparent orthographies relies on mapping smaller orthographic units to phonology, than reading opaque orthographies; but what are the neural mechanisms underlying this difference? Hebrew has a transparent (pointed) script used for beginners, and a non-transparent script used for skilled readers. The current study examined the developmental changes in brain regions associated with phonological and orthographic processes during reading pointed and un-pointed words. Our results highlight some changes that are universal in reading development, such as a developmental increase in frontal involvement (in bilateral inferior frontal gyrus (IFG) pars opercularis), and increase in left asymmetry (in IFG pars opercularis and superior temporal gyrus, STG) of the reading network. Our results also showed a developmental increase in activation in STG, which stands in contrast to previous studies in other orthographies. We further found an interaction of word length and diacritics in bilateral STG and VWFA across both groups. These findings suggest that children slightly adjust their reading depending on orthographic transparency, relying on smaller units when reading a transparent script and on larger units when reading an opaque script. Our results also showed that phonological abilities across groups correlated with activation in the VWFA, regardless of transparency, supporting the continued role of phonology at all levels of orthographic transparency. Our findings are consistent with multiple route reading models, in which both phonological and orthographic processing of multiple size units continue to play a role in children's reading of transparent and opaque scripts during reading development. The results further demonstrate the importance of taking into account differences between orthographies when constructing neural models of reading acquisition.

Animal models of developmental dyslexia: Where we are and what we are missing

Developmental dyslexia (DD) is a complex neurodevelopmental disorder and the most common learning disability among both school-aged children and across languages. Recently, sensory and cognitive mechanisms have been reported to be potential endophenotypes (EPs) for DD, and nine DD-candidate genes have been identified. Animal models have been used to investigate the etiopathological pathways that underlie the development of complex traits, as they enable the effects of genetic and/or environmental manipulations to be evaluated. Animal research designs have also been linked to cutting-edge clinical research questions by capitalizing on the use of EPs. For the present scoping review, we reviewed previous studies of murine models investigating the effects of DD-candidate genes. Moreover, we highlighted the use of animal models as an innovative way to unravel new insights behind the pathophysiology of reading (dis)ability and to assess cutting-edge preclinical models.

Reciprocal relations between reading skill and the neural basis of phonological awareness in 7- to 9-year-old children

By using a longitudinal design and functional magnetic resonance imaging (fMRI), our previous study (Wang et al., 2020) found a scaffolding effect of early phonological processing in the superior temporal gyrus (STG) in 6-year-old children on later behavioral reading skill in 7.5-year-old children. Other than this previous study, nothing is known about longitudinal change in the bidirectional relation between reading skill and phonological processing in the brain. To fill this gap, in the current study, we used the same experimental paradigm as in Wang et al. (2020) to measure children's reading skill and brain activity during an auditory phonological awareness task, but with children who were 7.5 years old at Time 1 (T1) and about 1.5 years later when they were 9 years old at Time 2 (T2). The phonological awareness task included both small grain (i.e., onset) and large grain (i.e., rhyme) conditions. In a univariate analysis, we found that better reading skill at T1 predicted lower brain activation in IFG at T2 for onset processing after controlling for brain activation and non-verbal IQ at T1. This suggests that early reading ability reduces the effort of phonemic access, thus supporting the refinement hypothesis. When using general psychophysiological interaction (gPPI), we found that higher functional connectivity from IFG to STG for rhyme processing at T1 predicted better reading skill at T2 after controlling for reading skill and non-verbal IQ at T1. This suggests that the early effectiveness of accessing rhyme representations scaffolds reading acquisition. As both results did not survive multiple comparison corrections, replication of these findings is needed. However, both findings are consistent with prior studies demonstrating that phonological access in the frontal lobe becomes important in older elementary school readers. Moreover, the refinement effect for onsets is consistent with the hypothesis that learning to read allows for better access of small grain phonology, and the scaffolding effect for rhymes supports the idea that reading progresses to larger grain orthography-to-phonology mapping in older skilled readers. The current study, along with our previous study on younger children, indicates that the development of reading skill is associated with (1) the early importance of the quality of the phonological representations to later access of these representations, and (2) early importance of small grain sizes to later development of large grain ones.

Resting-State Functional Magnetic Resonance Imaging Connectivity Between Semantic and Phonological Regions of Interest May Inform Language Targets in Aphasia

Purpose Brain imaging has provided puzzle pieces in the understanding of language. In neurologically healthy populations, the structure of certain brain regions is associated with particular language functions (e.g., semantics, phonology). In studies on focal brain damage, certain brain regions or connections are considered sufficient or necessary for a given language function. However, few of these account for the effects of lesioned tissue on the "functional" dynamics of the brain for language processing. Here, functional connectivity (FC) among semantic-phonological regions of interest (ROIs) is assessed to fill a gap in our understanding about the neural substrates of impaired language and whether connectivity strength can predict language performance on a clinical tool in individuals with aphasia. Method Clinical assessment of language, using the Western Aphasia Battery-Revised, and resting-state functional magnetic resonance imaging data were obtained for 30 individuals with chronic aphasia secondary to left-hemisphere stroke and 18 age-matched healthy controls. FC between bilateral ROIs was contrasted by group and used to predict Western Aphasia Battery-Revised scores. Results Network coherence was observed in healthy controls and participants with stroke. The left-right premotor cortex connection was stronger in healthy controls, as reported by New et al. (2015) in the same data set. FC of (a) connections between temporal regions, in the left hemisphere and bilaterally, predicted lexical-semantic processing for auditory comprehension and (b) ipsilateral connections between temporal and frontal regions in both hemispheres predicted access to semantic-phonological representations and processing for verbal production. Conclusions Network connectivity of brain regions associated with semantic-phonological processing is predictive of language performance in poststroke aphasia. The most predictive connections involved right-hemisphere ROIs-particularly those for which structural adaptions are known to associate with recovered word retrieval performance. Predictions may be made, based on these findings, about which connections have potential as targets for neuroplastic functional changes with intervention in aphasia. Supplemental Material https://doi.org/10.23641/asha.12735785.

Long-term Pingju Opera Training Induces Plasticity Changes in Cerebral Blood Flow: An Arterial Spin Labelling MRI Study

Professional Pingju actors have been shown to exhibit practice-induced plastic changes in spontaneous regional brain activity; however, whether these changes are present in resting-state regional cerebral blood flow (CBF) remains largely unclear. Here, twenty professional Pingju opera actors and 20 age-, sex-, and handedness-matched untrained subjects were recruited, and resting-state CBF maps were obtained by using a three-dimensional pseudocontinuous arterial spin labelling sequence. Voxel-based comparisons of the CBF maps between the two groups were performed with two-sample t-tests, and correlation analyses between the CBF changes and years of training in the actor group were conducted. In addition, the CBF connectivity between regions with CBF alterations and the whole brain was computed and compared between the two groups. Compared with untrained subjects, the actors showed significantly higher CBF in the right inferior temporal gyrus, right middle temporal gyrus, left temporal pole, and left inferior frontal gyrus, whereas significantly lower CBF was not found in the actor group (voxel-level uncorrected p < 0.001, cluster-level family-wise error corrected p < 0.05). Furthermore, there was no correlation between the mean CBF values from significantly different clusters and the years of training, and no significant alterations in CBF connectivity were found in the actor group. Overall, these results provided preliminary evidence that neural plastic changes in CBF are present in professional Pingju opera actors, which may correspond to specific experiences associated with Pingju opera training.

Repetition enhancement to voice identities in the dog brain

In the human speech signal, cues of speech sounds and voice identities are conflated, but they are processed separately in the human brain. The processing of speech sounds and voice identities is typically performed by non-primary auditory regions in humans and non-human primates. Additionally, these processes exhibit functional asymmetry in humans, indicating the involvement of distinct mechanisms. Behavioural studies indicate analogue side biases in dogs, but neural evidence for this functional dissociation is missing. In two experiments, using an fMRI adaptation paradigm, we presented awake dogs with natural human speech that either varied in segmental (change in speech sound) or suprasegmental (change in voice identity) content. In auditory regions, we found a repetition enhancement effect for voice identity processing in a secondary auditory region - the caudal ectosylvian gyrus. The same region did not show repetition effects for speech sounds, nor did the primary auditory cortex exhibit sensitivity to changes either in the segmental or in the suprasegmental content. Furthermore, we did not find evidence for functional asymmetry neither in the processing of speech sounds or voice identities. Our results in dogs corroborate former human and non-human primate evidence on the role of secondary auditory regions in the processing of suprasegmental cues, suggesting similar neural sensitivity to the identity of the vocalizer across the mammalian order.

Generating Natural, Intelligible Speech From Brain Activity in Motor, Premotor, and Inferior Frontal Cortices

Neural interfaces that directly produce intelligible speech from brain activity would allow people with severe impairment from neurological disorders to communicate more naturally. Here, we record neural population activity in motor, premotor and inferior frontal cortices during speech production using electrocorticography (ECoG) and show that ECoG signals alone can be used to generate intelligible speech output that can preserve conversational cues. To produce speech directly from neural data, we adapted a method from the field of speech synthesis called unit selection, in which units of speech are concatenated to form audible output. In our approach, which we call Brain-To-Speech, we chose subsequent units of speech based on the measured ECoG activity to generate audio waveforms directly from the neural recordings. Brain-To-Speech employed the user's own voice to generate speech that sounded very natural and included features such as prosody and accentuation. By investigating the brain areas involved in speech production separately, we found that speech motor cortex provided more information for the reconstruction process than the other cortical areas.

Neural representations of phonology in temporal cortex scaffold longitudinal reading gains in 5- to 7-year-old children

The objective of this study was to investigate whether phonological processes measured through brain activation are crucial for the development of reading skill (i.e. scaffolding hypothesis) and/or whether learning to read words fine-tunes phonology in the brain (i.e. refinement hypothesis). We specifically looked at how different grain sizes in two brain regions implicated in phonological processing played a role in this bidirectional relation. According to the dual-stream model of speech processing and previous empirical studies, the posterior superior temporal gyrus (STG) appears to be a perceptual region associated with phonological representations, whereas the dorsal inferior frontal gyrus (IFG) appears to be an articulatory region that accesses phonological representations in STG during more difficult tasks. 36 children completed a reading test outside the scanner and an auditory phonological task which included both small (i.e. onset) and large (i.e. rhyme) grain size conditions inside the scanner when they were 5.5-6.5 years old (Time 1) and once again approximately 1.5 years later (Time 2). To study the scaffolding hypothesis, a regression analysis was carried out by entering brain activation in either STG or IFG for either small (onset > perceptual) or large (rhyme > perceptual) grain size phonological processing at T1 as the predictors and reading skill at T2 as the dependent measure, with several covariates of no interest included. To study the refinement hypothesis, the regression analysis included reading skill at T1 as the predictor and brain activation in either STG or IFG for either small or large grain size phonological processing at T2 as the dependent measures, with several covariates of no interest included. We found that only posterior STG, regardless of grain size, was predictive of reading gains. Parallel models with only behavioral accuracy were not significant. Taken together, our results suggest that the representational quality of phonology in temporal cortex is crucial for reading development. Moreover, our study provides neural evidence supporting the scaffolding hypothesis, suggesting that brain measures of phonology could be helpful in early identification of reading difficulties.

The ConDialInt Model: Condensation, Dialogality, and Intentionality Dimensions of Inner Speech Within a Hierarchical Predictive Control Framework

Inner speech has been shown to vary in form along several dimensions. Along condensation, condensed inner speech forms have been described, that are supposed to be deprived of acoustic, phonological and even syntactic qualities. Expanded forms, on the other extreme, display articulatory and auditory properties. Along dialogality, inner speech can be monologal, when we engage in internal soliloquy, or dialogal, when we recall past conversations or imagine future dialogs involving our own voice as well as that of others addressing us. Along intentionality, it can be intentional (when we deliberately rehearse material in short-term memory) or it can arise unintentionally (during mind wandering). We introduce the ConDialInt model, a neurocognitive predictive control model of inner speech that accounts for its varieties along these three dimensions. ConDialInt spells out the condensation dimension by including inhibitory control at the conceptualization, formulation or articulatory planning stage. It accounts for dialogality, by assuming internal model adaptations and by speculating on neural processes underlying perspective switching. It explains the differences between intentional and spontaneous varieties in terms of monitoring. We present an fMRI study in which we probed varieties of inner speech along dialogality and intentionality, to examine the validity of the neuroanatomical correlates posited in ConDialInt. Condensation was also informally tackled. Our data support the hypothesis that expanded inner speech recruits speech production processes down to articulatory planning, resulting in a predicted signal, the inner voice, with auditory qualities. Along dialogality, covertly using an avatar's voice resulted in the activation of right hemisphere homologs of the regions involved in internal own-voice soliloquy and in reduced cerebellar activation, consistent with internal model adaptation. Switching from first-person to third-person perspective resulted in activations in precuneus and parietal lobules. Along intentionality, compared with intentional inner speech, mind wandering with inner speech episodes was associated with greater bilateral inferior frontal activation and decreased activation in left temporal regions. This is consistent with the reported subjective evanescence and presumably reflects condensation processes. Our results provide neuroanatomical evidence compatible with predictive control and in favor of the assumptions made in the ConDialInt model.

Repeated Vowel Production Affects Features of Neural Activity in Sensorimotor Cortex

The sensorimotor cortex is responsible for the generation of movements and interest in the ability to use this area for decoding speech by brain–computer interfaces has increased recently. Speech decoding is challenging however, since the relationship between neural activity and motor actions is not completely understood. Non-linearity between neural activity and movement has been found for instance for simple finger movements. Despite equal motor output, neural activity amplitudes are affected by preceding movements and the time between movements. It is unknown if neural activity is also affected by preceding motor actions during speech. We addressed this issue, using electrocorticographic high frequency band (HFB; 75–135 Hz) power changes in the sensorimotor cortex during discrete vowel generation. Three subjects with temporarily implanted electrode grids produced the /i/ vowel at repetition rates of 1, 1.33 and 1.66 Hz. For every repetition, the HFB power amplitude was determined. During the first utterance, most electrodes showed a large HFB power peak, which decreased for subsequent utterances. This result could not be explained by differences in performance. With increasing duration between utterances, more electrodes showed an equal response to all repetitions, suggesting that the duration between vowel productions influences the effect of previous productions on sensorimotor cortex activity. Our findings correspond with previous studies for finger movements and bear relevance for the development of brain-computer interfaces that employ speech decoding based on brain signals, in that past utterances will need to be taken into account for these systems to work accurately.