Modulation of tonotopic ventral medial geniculate body is behaviorally relevant for speech recognition

Abstract

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

Modulation of the primary auditory thalamus when recognising speech in noise

“…In addition to addressing the main hypothesis of the present paper, the data also allowed the testing for replication of previous findings (Díaz et al, 2012;Mihai et al, 2019;von Kriegstein et al, 2008), i.e., a test for a main effect of task (speech -speaker) in left and right MGB and a test for a correlation between speech recognition performance and main effect of task across participants in the left MGB.…”

“…We focused on the left vMGB for two reasons. First, its response showed behavioural relevance for speech recognition in previous studies (Mihai et al, 2019;von Kriegstein et al, 2008). Second, a study on developmental dyslexia -a condition that is often associated with speech-in-noise recognition difficulties (Chandrasekaran et al, 2009;Ziegler et al, 2009) -showed reduced task-dependent modulation of the left MGB in comparison to controls (Díaz et al, 2012).…”

“…This response difference holds even if the stimulus input is the same (Díaz et al, 2012;von Kriegstein et al, 2008). This task-dependent modulation seems to be behaviorally relevant for speech recognition: performance level in auditory speech recognition was positively correlated with the amount of task-dependent modulation in the MGB of the left hemisphere (Mihai et al, 2019;von Kriegstein et al, 2008). This behaviourally relevant task-dependent modulation was located in the ventral part of the MGB (vMGB), which is the primary subsection of the MGB, but not in other MGB subsections (Mihai et al, 2019).…”

“…This task-dependent modulation seems to be behaviorally relevant for speech recognition: performance level in auditory speech recognition was positively correlated with the amount of task-dependent modulation in the MGB of the left hemisphere (Mihai et al, 2019;von Kriegstein et al, 2008). This behaviourally relevant task-dependent modulation was located in the ventral part of the MGB (vMGB), which is the primary subsection of the MGB, but not in other MGB subsections (Mihai et al, 2019). These findings could fit the Bayesian brain hypothesis on cortico-subcortical interactions: cerebral cortex areas provide dynamic predictions about the incoming sensory input to the sensory thalamus to optimally encode the trajectory of the fast-varying and predictable speech input (Díaz et al, 2012;von Kriegstein et al, 2008).…”

“…In addition to testing our main hypothesis, the design also (i) served to test for replicability of previous findings on the involvement of the MGB in speech recognition as well as its relevance for speech recognition behaviour (Mihai et al, 2019;von Kriegstein et al, 2008), and (ii) allowed to explore the role of the inferior colliculus (IC) -the midbrain station of the auditory sensory pathway -in speech and speech-in-noise recognition.…”