Modulation of tonotopic ventral MGB is behaviorally relevant for speech recognition

Abstract

Impact statement: Ultra-high field neuroimaging dissects the ventral medial geniculate 17 body (vMGB) of the primary auditory pathway from other MGB subregions and reveals that 18 vMGB top-down modulation is relevant for speech recognition. Abstract 23Sensory thalami are central sensory pathway stations for information processing. Their role for human 24 cognition and perception, however, remains unclear. Recent evidence suggests an involvement of the 25 sensory thalami in speech recognition. In particular, the auditory thalamus (medial geniculate body, MGB) 26 response is modulated by speech recognition tasks and the amount of this task-dependent modulation is 27 associated with speech recognition abilities. Here we tested the specific hypothesis that this behaviorally 28 relevant modulation is present in the MGB subsection that corresponds to the primary auditory pathway 29 (i.e., the ventral MGB [vMGB]). We used ultra-high field 7T fMRI to identify the vMGB, and found a 30 significant positive correlation between the amount of task-dependent modulation and the speech 31 recognition performance across participants within left vMGB, but not within the other MGB subsections. 32These results imply that modulation of thalamic driving input to the auditory cortex facilitates speech 33 recognition. 34

Modulation of the primary auditory thalamus when recognising speech in noise

“…A task-dependent modulation for speech recognition means that sensory thalamus responses were higher for speech tasks (that emphasized recognition of fast-varying speech properties) in contrast to control tasks (that required recognition of relatively constant properties of the speech signal, such as the speaker identity or the sound intensity level). The studies also found that the performance level in auditory speech recognition was positively correlated with the task-dependent modulation in the MGB of the left hemisphere (von Kriegstein, Patterson, and Griffiths 2008;Mihai et al 2019).…”

“…From Wernicke's research (Wernicke 1874) all the way up to current findings, neuroscientific models of speech recognition have mostly focused on cerebral cortex mechanisms (Hickok and Small 2015;Friederici and Gierhan 2013). Recent findings, however, suggest that a full understanding of speech recognition mechanisms is impossible without understanding cerebral cortex feedback mechanisms to the subcortical sensory pathways (von Kriegstein, Patterson, and Griffiths 2008;Diaz et al 2012;Dí az, Blank, and von Kriegstein 2018;Mihai et al 2019;Chandrasekaran et al 2009;Chandrasekaran, Kraus, and Wong 2011), in particular, to the sensory thalami (von Kriegstein,et al 2008;Diaz et al 2012;Dí az et al 2018;Mihai et al 2019).…”

“…The classic view, that the sensory thalamus is a passive relay station (Squire et al 2012) has been by-and-large abandoned over the last two decades. It has become accepted as a structure that is modulated by cognitive demands (Saalmann and Kastner 2015;Saalmann and Kastner 2011;Haynes, Deichmann, and Rees 2005;Antunes and Malmierca 2011;OConnor et al 2002;McAlonan, Cavanaugh, and Wurtz 2008;Diaz et al 2012;Mihai et al 2019;von Kriegstein, Patterson, and Griffiths 2008;Dí az, Blank, and von Kriegstein 2018).…”

“…The ventral MGB also receives modulatory input from the cerebral cortex (Sherman and Guillery 1998). Technical advances have only recently provided such high spatial resolution that allows research on the function of these structures in humans in vivo (Denison et al 2014; Moerel et al 2015, Mihai et al 2019. Using these techniques, we previously showed that the behaviourally relevant task-dependent modulation in the left MGB for speech is located in the vMGB (Mihai et al 2019), i.e., the first-order sensory thalamus.…”

“…We therefore tested, whether the taskdependent modulation of the left vMGB for speech is higher when the speech stimuli are heard in a noisy as opposed to a clear background. To do this, we used ultra-high field fMRI at 7 T and a design that has been shown to elicit task-dependent modulation of the vMGB in previous studies (von Kriegstein et al 2008;Diaz et al 2012;Mihai et al 2019). We complemented the design by a noise factor, i.e., the speech stimuli were presented with and without background noise.…”