Investigating the Neural Basis of Theta Burst Stimulation to Premotor Cortex on Emotional Vocalization Perception: A Combined TMS-fMRI Study

Previous studies have established a role for premotor cortex in the processing of auditory emotional vocalizations. Inhibitory continuous theta burst transcranial magnetic stimulation (cTBS) applied to right premotor cortex selectively increases the reaction time to a same-different task, implying a causal role for right ventral premotor cortex (PMv) in the processing of emotional sounds. However, little is known about the functional networks to which PMv contribute across the cortical hemispheres. In light of these data, the present study aimed to investigate how and where in the brain cTBS affects activity during the processing of auditory emotional vocalizations. Using functional neuroimaging, we report that inhibitory cTBS applied to the right premotor cortex (compared to vertex control site) results in three distinct response profiles: following stimulation of PMv, widespread frontoparietal cortices, including a site close to the target site, and parahippocampal gyrus displayed an increase in activity, whereas the reverse response profile was apparent in a set of midline structures and right IFG. A third response profile was seen in left supramarginal gyrus in which activity was greater post-stimulation at both stimulation sites. Finally, whilst previous studies have shown a condition specific behavioral effect following cTBS to premotor cortex, we did not find a condition specific neural change in BOLD response. These data demonstrate a complex relationship between cTBS and activity in widespread neural networks and are discussed in relation to both emotional processing and the neural basis of cTBS

Exploring the Roles of Spectral Detail and Intonation Contour in Speech Intelligibility:An fMRI Study

The melodic contour of speech forms an important perceptual aspect of tonal and nontonal languages and an important limiting factor on the intelligibility of speech heard through a cochlear implant. Previous work exploring the neural correlates of speech comprehension identified a left-dominant pathway in the temporal lobes supporting the extraction of an intelligible linguistic message, whereas the right anterior temporal lobe showed an overall preference for signals clearly conveying dynamic pitch information. The current study combined modulations of overall intelligibility (through vocoding and spectral inversion) with a manipulation of pitch contour (normal vs. falling) to investigate the processing of spoken sentences in functional MRI. Our overall findings replicate and extend those of Scott et al., whereas greater sentence intelligibility was predominately associated with increased activity in the left STS, the greatest response to normal sentence melody was found right superior temporal gyrus. These data suggest a spatial distinction between brain areas associated with intelligibility and those involved in the processing of dynamic pitch information in speech. By including a set of complexity-matched unintelligible conditions created by spectral inversion, this is additionally the first study reporting a fully factorial exploration of spectrotemporal complexity and spectral inversion as they relate to the neural processing of speech intelligibility. Perhaps surprisingly, there was no evidence for an interaction between the two factors—we discuss the implications for the processing of sound and speech in the dorsolateral temporal lobes

You talkin' to me? Communicative talker gaze activates left-lateralized superior temporal cortex during perception of degraded speech.

Neuroimaging studies of speech perception have consistently indicated a left-hemisphere dominance in the temporal lobes' responses to intelligible auditory speech signals (McGettigan and Scott, 2012). However, there are important communicative cues that cannot be extracted from auditory signals alone, including the direction of the talker's gaze. Previous work has implicated the superior temporal cortices in processing gaze direction, with evidence for predominantly right-lateralized responses (Carlin & Calder, 2013). The aim of the current study was to investigate whether the lateralization of responses to talker gaze differs in an auditory communicative context. Participants in a functional MRI experiment watched and listened to videos of spoken sentences in which the auditory intelligibility and talker gaze direction were manipulated factorially. We observed a left-dominant temporal lobe sensitivity to the talker's gaze direction, in which the left anterior superior temporal sulcus/gyrus and temporal pole showed an enhanced response to direct gaze - further investigation revealed that this pattern of lateralization was modulated by auditory intelligibility. Our results suggest flexibility in the distribution of neural responses to social cues in the face within the context of a challenging speech perception task

Dissociating Object Directed and Non-Object Directed Action in the Human Mirror System; Implications for Theories of Motor Simulation

Mirror neurons are single cells found in macaque premotor and parietal cortices that are active during action execution and observation. In non-human primates, mirror neurons have only been found in relation to object-directed movements or communicative gestures, as non-object directed actions of the upper limb are not well characterized in non-human primates. Mirror neurons provide important evidence for motor simulation theories of cognition, sometimes referred to as the direct matching hypothesis, which propose that observed actions are mapped onto associated motor schemata in a direct and automatic manner. This study, for the first time, directly compares mirror responses, defined as the overlap between action execution and observation, during object directed and meaningless non-object directed actions. We present functional MRI data that demonstrate a clear dissociation between object directed and non-object directed actions within the human mirror system. A premotor and parietal network was preferentially active during object directed actions, whether observed or executed. Moreover, we report spatially correlated activity across multiple voxels for observation and execution of an object directed action. In contrast to predictions made by motor simulation theory, no similar activity was observed for non-object directed actions. These data demonstrate that object directed and meaningless non-object directed actions are subserved by different neuronal networks and that the human mirror response is significantly greater for object directed actions. These data have important implications for understanding the human mirror system and for simulation theories of motor cognition. Subsequent theories of motor simulation must account for these differences, possibly by acknowledging the role of experience in modulating the mirror response

Individual overlaps for Observe and Execute in objected directed and non-object directed action.

<p>A mask was used to restrict our analysis to regions significantly active in Observe and Execute conditions (voxels active for all four conditions, p<0,05; within an anatomically defined mask of premotor and parietal regions). These individual masks vary across individuals in widespread premotor and parietal cortices bilaterally (a). Regions of highest overlap are seen in green. The coordinates of peak overlap were −34 −59 64, 36 −42 52, −48 2 35, and −42, −9 58. Within these individual masks, we then looked at the mean correlation between Observe and Execute for the two difference action conditions; object directed and non-object directed. The mean correlation between Observe and Execute was highly significantly greater for object directed action compared to non-object directed action (b).</p

Mirror responses: activity common to execution and observation.

<p>Inclusive masking was used in order to look at significant activity common to both execution and observation conditions. BOLD responses to Observe_Trans+Execute_Trans were seen in premotor cortex, dorsal parietal cortex in both hemispheres and right lateral occipital cortex (a, orange). The same approach for Observe_Intrans+Execute_Intrans revealed significant activity in both contrasts in left occipital cortex only (a, blue). A direct comparison of activity common to execution and observation of an object directed actions more than an non-object directed action (Observe_Trans>Observe_Intrans)+(Execute_Trans>Execute_Intrans) allowed us to highlight voxels that are commonly activated in observing and executing an object-directed grasp more than executing and observing non-object directed movement. This analysis revealed significant activations in bilateral premotor and parietal cortices (b) (28 −48 56, −28 −52 58, 28 −14 56, −30 −4 60, −36 −38 52). The reverse comparison, (Observe_Intrans>Observe_Trans)+(Execute_Intrans>Execute_Trans), revealed no significant activity.</p

Whole brain analyses of spatial correlation.

<p>In addition to the ROI analysis shown in Figure, we also carried out a brain wide search in order to see if there were any other cortical regions displaying a spatial correlation between Execute and Observe conditions. A spherical searchlight was applied to the whole brain and significant correlations were compared for Observe Object directed action and Execute Object directed action (Observe_Trans_Execute_Trans), and Observe Non-object directed action and Execute Non-object directed action (Observe_Intrans_Execute_Intrans). Figure (a) shows spatial correlations were greater for Observe_Trans_Execute_Trans compared to Observe_Intrans_Execute_Intrans in left frontal cortex, inferior frontal gyrus and postcentral gyrus (BA 3). The lower panel shows an anticorrelation in left postcentral sulcus that is present for Observe_Trans_Execute_Trans but not for Observe_Intrans_Execute_Intrans (b).</p