Slip of the tongue: Implications for evolution and language development

3D directional tuning in the orofacial sensorimotor cortex during natural feeding and drinking

Directional tongue movements are essential for vital behaviors, such as feeding and speech, to position food for chewing and swallowing safely and to position the tongue for accurate sound production. While directional tuning has been well-studied in the arm region of the sensorimotor cortex during reaching tasks, little is known about how 3D tongue direction is encoded in the orofacial region during natural behaviors. Understanding how tongue direction is represented in the brain has important implications for improving rehabilitation for people with orolingual dysfunctions. The goal of this study is to investigate how 3D direction of tongue movement is encoded in the orofacial sensorimotor cortex (OSMCx) during feeding and drinking, and how this process is affected by the loss of oral sensation. Using biplanar video-radiography to track implanted markers in the tongue of behaving non-human primates (Macaca mulatta), 3D positional data was recorded simultaneously with spiking activity in primary motor (MIo) and somatosensory (SIo) areas of the orofacial cortex using chronically implanted microelectrode arrays. In some sessions, tasks were preceded by bilateral nerve block injections to the sensory branches of the trigeminal nerve. Modulation to the 3D tongue direction was found in a majority of MIo but not SIo neurons during feeding, while the majority of neurons in both areas were modulated to the direction of tongue protrusion during drinking. Following sensory loss, the proportion of directionally tuned neurons decreased and shifts in the distribution of preferred direction were observed in OSMCx neurons. Overall, we show that 3D directional tuning of MIo and SIo to tongue movements varies with behavioral tasks and availability of sensory information.

The Feel of Speech: Multisystem and Polymodal Somatosensation in Speech Production

PURPOSE

The oral structures such as the tongue and lips have remarkable somatosensory capacities, but understanding the roles of somatosensation in speech production requires a more comprehensive knowledge of somatosensation in the speech production system in its entirety, including the respiratory, laryngeal, and supralaryngeal subsystems. This review was conducted to summarize the system-wide somatosensory information available for speech production.

METHOD

The search was conducted with PubMed/Medline and Google Scholar for articles published until November 2023. Numerous search terms were used in conducting the review, which covered the topics of psychophysics, basic and clinical behavioral research, neuroanatomy, and neuroscience.

RESULTS AND CONCLUSIONS

The current understanding of speech somatosensation rests primarily on the two pillars of psychophysics and neuroscience. The confluence of polymodal afferent streams supports the development, maintenance, and refinement of speech production. Receptors are both canonical and noncanonical, with the latter occurring especially in the muscles innervated by the facial nerve. Somatosensory representation in the cortex is disproportionately large and provides for sensory interactions. Speech somatosensory function is robust over the lifespan, with possible declines in advanced aging. The understanding of somatosensation in speech disorders is largely disconnected from research and theory on speech production. A speech somatoscape is proposed as the generalized, system-wide sensation of speech production, with implications for speech development, speech motor control, and speech disorders.

Beyond language: The unspoken sensory-motor representation of the tongue in non-primates, non-human and human primates

The English idiom "on the tip of my tongue" commonly acknowledges that something is known, but it cannot be immediately brought to mind. This phrase accurately describes sensorimotor functions of the tongue, which are fundamental for many tongue-related behaviors (e.g., speech), but often neglected by scientific research. Here, we review a wide range of studies conducted on non-primates, non-human and human primates with the aim of providing a comprehensive description of the cortical representation of the tongue's somatosensory inputs and motor outputs across different phylogenetic domains. First, we summarize how the properties of passive non-noxious mechanical stimuli are encoded in the putative somatosensory tongue area, which has a conserved location in the ventral portion of the somatosensory cortex across mammals. Second, we review how complex self-generated actions involving the tongue are represented in more anterior regions of the putative somato-motor tongue area. Finally, we describe multisensory response properties of the primate and non-primate tongue area by also defining how the cytoarchitecture of this area is affected by experience and deafferentation.

Interaction between grasping and articulation: How vowel and consonant pronunciation influences precision and power grip responses

Grasping and mouth movements have been proposed to be integrated anatomically, functionally and evolutionarily. In line with this, we have shown that there is a systematic interaction between particular speech units and grip performance. For example, when the task requires pronouncing a speech unit simultaneously with grasp response, the speech units [i] and [t] are associated with relatively rapid and accurate precision grip responses, while [ɑ] and [k] are associated with power grip responses. This study is aimed at complementing the picture about which vowels and consonants are associated with these grasp types. The study validated our view that the high-front vowels and the alveolar consonants are associated with precision grip responses, while low and high-back vowels as well as velar consonants or those whose articulation involves the lowering of the tongue body are associated with power grip responses. This paper also proposes that one reason why small/large concepts are associated with specific speech sounds in the sound-magnitude symbolism is because articulation of these sounds is programmed within the overlapping mechanisms of precision or power grasping.

Promoting Executive Function Skills in Preschoolers Using a Play-Based Program

In recent years, play has been shown to be a powerful means to enhance learning and brain development. It is also known that through play children enhance their executive function (EF) skills. Furthermore, well-developed EF in preschoolers has been shown to be an important predictor for later academic and life success. Armed with this information a program, Building Brains and Futures (BBF), for developing EF through play was designed for 3–5-year-old. The program consisted of 10 simple, fun, and interactive games selected to enhance various facets of EF. The 10 games included were: dimensional change card sort, lips and ears, block building, musical freeze, opposites, pretend play, red light/green light, shared project, Simon says, and wait for it. The program was implemented with a group of children shown to have challenges with respect to kindergarten readiness. The approach was first, to build adult capability by sharing knowledge of brain development, EF, and the importance of play with educators, caregivers, and parents. Second, to build skills in delivering the program in the school setting. Children engaged with the program of games for a minimum of 6 weeks. Their performance on a battery of direct measures of EF, language, and motor skills, were recorded before and after the program. The results showed improvement in all three domains. In addition, adopters of the BBF program reported it was easily and successfully integrated into their existing preschool curricula. The importance of intentional adult directed play in building developmental learning, including EF, is discussed.

Connection between movements of mouth and hand: Perspectives on development and evolution of speech

Mounting evidence shows interaction between manipulative hand movements and movements of tongue, lips and mouth in a vocal and non-vocal context. The current article reviews this evidence and discusses its contribution to perspectives of development and evolution of speech. In particular, the article aims to present novel insight on how processes controlling the two primary grasp components of manipulative hand movements, the precision and power grip, might be systematically connected to motor processes involved in producing certain articulatory gestures. This view assumes that due to these motor overlaps between grasping and articulation, development of these grip types in infancy can facilitate development of specific articulatory gestures. In addition, the hand-mouth connections might have even boosted the evolution of some articulatory gestures. This account also proposes that some semantic sound-symbolic pairings between a speech sound and a referent concept might be partially based on these hand-mouth interactions.

Sensorimotor lateralization scaffolds cognitive specialization

In this chapter, we review hemispheric differences for sensorimotor function and cognitive abilities. Specifically, we examine the left-hemisphere specialization for visuomotor control and its interplay with language, executive function, and musical training. Similarly, we discuss right-hemisphere lateralization for haptic processing and its relationship to spatial and numerical processing. We propose that cerebral lateralization for sensorimotor functions served as a foundation for the development of higher cognitive abilities and their hemispheric functional specialization. We further suggest that sensorimotor and cognitive functions are inextricably linked. Based on the studies discussed in this chapter our view is that sensorimotor control serves as a loom upon which the fibers of language, executive function, spatial, and numerical processing are woven together to create the fabric of cognition.

The Preference for Pointing With the Hand Is Not Universal

Pointing is a cornerstone of human communication, but does it take the same form in all cultures? Manual pointing with the index finger appears to be used universally, and it is often assumed to be universally preferred over other forms. Non-manual pointing with the head and face has also been widely attested, but it is usually considered of marginal significance, both empirically and theoretically. Here, we challenge this assumed marginality. Using a novel communication task, we investigated pointing preferences in the Yupno of Papua New Guinea and in U.S. undergraduates. Speakers in both groups pointed at similar rates, but form preferences differed starkly: The Yupno participants used non-manual pointing (nose- and head-pointing) numerically more often than manual pointing, whereas the U.S. participants stuck unwaveringly to index-finger pointing. The findings raise questions about why groups differ in their pointing preferences and, more broadly, about why humans communicate in the ways they do.

Tongue protrusions modify the syntax of skilled reaching for food by the mouse: Evidence for flexibility in action selection and shared hand/mouth central modulation of action

Skilled reaching for food by the laboratory mouse has the appearance of an action pattern with a distinctive syntax in which ten submovements occur in an orderly sequence. A mouse locates the food by Sniffing, Lifts, Aims, Advances, and Shapes the hand to Pronate it over a food target that it Grasps, Retracts, and Withdraws to Release to its mouth for eating. The structure of the individual actions in the chain are useful for the study of the mouse motor system and contribute to the use of the mouse as a model of human neurological conditions. The present study describes tongue protrusions that modify the syntax of reaching by occurring at the point of the reaching action at which the hand is at the Aim position. Tongue protrusions were not related to reaching success and were not influenced by training. Tongue protrusions were more likely to occur in the presence of a food target than with reaches made when food was absent. There were vast individual differences; some mice always make tongue protrusions while other mice never make tongue protrusions. That the syntax of reaching can be altered by the insertion of a surrogate (co-occurring) movement adds to a growing body of evidence that skilled reaching is assembled from a number of relatively independent actions, each with its own sensorimotor control that are subject to central modulation. That tongue and hand reaching movements can co-occur suggests a privileged relation between neural mechanisms that control movements of the tongue and hand.

Mismatch negativity (MMN) to speech sounds is modulated systematically by manual grip execution

Manual actions and speech are connected: for example, grip execution can influence simultaneous vocalizations and vice versa. Our previous studies show that the consonant [k] is associated with the power grip and the consonant [t] with the precision grip. Here we studied whether the interaction between speech sounds and grips could operate already at a pre-attentive stage of auditory processing, reflected by the mismatch-negativity (MMN) component of the event-related potential (ERP). Participants executed power and precision grips according to visual cues while listening to syllable sequences consisting of [ke] and [te] utterances. The grips modulated the MMN amplitudes to these syllables in a systematic manner so that when the deviant was [ke], the MMN response was larger with a precision grip than with a power grip. There was a converse trend when the deviant was [te]. These results suggest that manual gestures and speech can interact already at a pre-attentive processing level of auditory perception, and show, for the first time that manual actions can systematically modulate the MMN.

Connections of Grasping and Horizontal Hand Movements with Articulation in Czech Speakers

We have recently shown in Finnish speakers that articulation of certain vowels and consonants has a systematic influence on simultaneous grasp actions as well as on forward and backward hand movements. Here we studied whether these effects generalize to another language, namely Czech. We reasoned that if the results generalized to another language environment, it would suggest that the effects arise through other processes than language-dependent semantic associations. Rather, the effects would be likely to arise through language-independent interactions between processes that plan articulatory gestures and hand movements. Participants were presented with visual stimuli specifying articulations to be uttered (e.g., A or I), and they were required to produce a manual response concurrently with the articulation. In Experiment 1 they responded with a precision or a power grip, whereas in Experiment 2 they responded with a forward or a backward hand movement. The grip congruency effect was fully replicated: the consonant [k] and the vowel [α] were associated with power grip responses, while the consonant [t] and the vowel [i] were associated with precision grip responses. The forward/backward congruency effect was replicated with vowels [α], [o], which were associated with backward movement and with [i], which was associated with forward movement, but not with consonants [k] and [t]. These findings suggest that the congruency effects mostly reflect interaction between processes that plan articulatory gestures and hand movements with an exception that the forward/backward congruency effect might only work with vowel articulation.

Systematic Influence of Perceived Grasp Shape on Speech Production

Previous research has shown that precision and power grip performance is consistently influenced by simultaneous articulation. For example, power grip responses are performed relatively fast with the open-back vowel [a], whereas precision grip responses are performed relatively fast with the close-front vowel [i]. In the present study, the participants were presented with a picture of a hand shaped to the precision or power grip. They were required to pronounce speech sounds according to the front/above perspective of the hand. The results showed that not only the grip performance is affected by simultaneously pronouncing the speech sound but also the production of speech sound can be affected by viewing an image of a grip. The precision grip stimulus triggered relatively rapid production of the front-close vowel [i]. In contrast, the effect related to the power grip stimulus was mostly linked to the vertical dimension of the pronounced vowel since this stimulus triggered relatively rapid production of the back-open vowel [a] and back-mid-open vowel [o] while production of the back-close vowel [u] was not influenced by it. The fact that production of the dorsal consonant [k] or coronal consonant [t] were not influenced by these stimuli suggests that the effect was not associated with a relative front-back tongue shape of the articulation in the absence of changes in any vertical articulatory components. These findings provide evidence for an intimate interaction between certain articulatory gestures and grip types, suggesting that an overlapping visuomotor network operates for planning articulatory gestures and grasp actions.