Group and individual variability in speech production networks during delayed auditory feedback.

Altering reafferent sensory information can have a profound effect on motor output. Introducing a short delay [delayed auditory feedback (DAF)] during speech production results in modulations of voice and loudness, and produces a range of speech dysfluencies. The ability of speakers to resist the effects of delayed feedback is variable yet it is unclear what neural processes underlie differences in susceptibility to DAF. Here, susceptibility to DAF is investigated by looking at the neural basis of within and between subject changes in speech fluency under 50 and 200 ms delay conditions. Using functional magnetic resonance imaging, networks involved in producing speech under two levels of DAF were identified, lying largely within networks active during normal speech production. Independent of condition, fluency ratings were associated with midbrain activity corresponding to periaqueductal grey matter. Across subject variability in ability to produce normal sounding speech under a 200 ms delay was associated with activity in ventral sensorimotor cortices, whereas ability to produce normal sounding speech under a 50 ms delay was associated with left inferior frontal gyrus activity. These data indicate whilst overlapping cortical mechanisms are engaged for speaking under different delay conditions, susceptibility to different temporal delays in speech feedback may involve different processes.

Individual differences in laughter perception reveal roles for mentalizing and sensorimotor systems in the evaluation of emotional authenticity.

Humans express laughter differently depending on the context: polite titters of agreement are very different from explosions of mirth. Using functional MRI, we explored the neural responses during passive listening to authentic amusement laughter and controlled, voluntary laughter. We found greater activity in anterior medial prefrontal cortex (amPFC) to the deliberate, Emitted Laughs, suggesting an obligatory attempt to determine others' mental states when laughter is perceived as less genuine. In contrast, passive perception of authentic Evoked Laughs was associated with greater activity in bilateral superior temporal gyri. An individual differences analysis found that greater accuracy on a post hoc test of authenticity judgments of laughter predicted the magnitude of passive listening responses to laughter in amPFC, as well as several regions in sensorimotor cortex (in line with simulation accounts of emotion perception). These medial prefrontal and sensorimotor sites showed enhanced positive connectivity with cortical and subcortical regions during listening to involuntary laughter, indicating a complex set of interacting systems supporting the automatic emotional evaluation of heard vocalizations.

Articulatory movements modulate auditory responses to speech.

Production of actions is highly dependent on concurrent sensory information. In speech production, for example, movement of the articulators is guided by both auditory and somatosensory input. It has been demonstrated in non-human primates that self-produced vocalizations and those of others are differentially processed in the temporal cortex. The aim of the current study was to investigate how auditory and motor responses differ for self-produced and externally produced speech. Using functional neuroimaging, subjects were asked to produce sentences aloud, to silently mouth while listening to a different speaker producing the same sentence, to passively listen to sentences being read aloud, or to read sentences silently. We show that that separate regions of the superior temporal cortex display distinct response profiles to speaking aloud, mouthing while listening, and passive listening. Responses in anterior superior temporal cortices in both hemispheres are greater for passive listening compared with both mouthing while listening, and speaking aloud. This is the first demonstration that articulation, whether or not it has auditory consequences, modulates responses of the dorsolateral temporal cortex. In contrast posterior regions of the superior temporal cortex are recruited during both articulation conditions. In dorsal regions of the posterior superior temporal gyrus, responses to mouthing and reading aloud were equivalent, and in more ventral posterior superior temporal sulcus, responses were greater for reading aloud compared with mouthing while listening. These data demonstrate an anterior-posterior division of superior temporal regions where anterior fields are suppressed during motor output, potentially for the purpose of enhanced detection of the speech of others. We suggest posterior fields are engaged in auditory processing for the guidance of articulation by auditory information.

Hedonic and informational functions of the human orbitofrontal cortex.

Functional imaging studies have revealed roles for orbitofrontal cortex (OFC) in reward processing and decision making. In many situations, rewards signal that the current behavior should be maintained, whereas punishments cue a change in behavior. Thus, hedonic responses to reinforcers are conflated with their function as behavioral cues. In an attempt to disambiguate these functions, we performed a functional magnetic resonance imaging study of a 2-choice decision-making task. After each trial, subjects were rewarded or punished and independently provided with a cue to maintain or change behavior. We identified key regions of OFC involved in these processes. An anterior medial focus responded to reward, whereas bilateral lateral foci responded to punishment. The right-sided lateral region that responded to punishment also responded to cues for behavior change (shift), whereas a more ventral and anterior bilateral region responded to cues for behavioral maintenance (stay). The right-sided stay region responded specifically when stay cues were combined with punishment. These results support the view that OFC codes both hedonic responses to reinforcers and their behavioral consequences. Punishments and shift cues are associated with the same right lateral OFC focus, suggesting a fundamental connection between emotive response to negative reinforcement and use of negative information to cue behavioral change.

Medial orbitofrontal cortex codes relative rather than absolute value of financial rewards in humans.

Functional imaging studies in recent years have confirmed the involvement of orbitofrontal cortex (OFC) in human reward processing and have suggested that OFC responses are context-dependent. A seminal electrophysiological experiment in primates taught animals to associate abstract visual stimuli with differently valuable food rewards. Subsequently, pairs of these learned abstract stimuli were presented and firing of OFC neurons to the medium-value stimulus was measured. OFC firing was shown to depend on the relative value context. In this study, we developed a human analogue of this paradigm and scanned subjects using functional magnetic resonance imaging. The analysis compared neuronal responses to two superficially identical events, which differed only in terms of the preceding context. Medial OFC response to the same perceptual stimulus was greater when the stimulus predicted the more valuable of two rewards than when it predicted the less valuable. Additional responses were observed in other components of reward circuitry, the amygdala and ventral striatum. The central finding is consistent with the primate results and suggests that OFC neurons code relative rather than absolute reward value. Amygdala and striatal involvement in coding reward value is also consistent with recent functional imaging data. By using a simpler and less confounded paradigm than many functional imaging studies, we are able to demonstrate that relative financial reward value per se is coded in distinct subregions of an extended reward and decision-making network.

Do sentences with unaccusative verbs involve syntactic movement? Evidence from neuroimaging.

This study focuses on the neural processing of English sentences containing unergative, unaccusative and transitive verbs. We demonstrate common responses in bilateral superior temporal gyri in response to listening to sentences containing unaccusative and transitive verbs compared to unergative verbs; we did not detect any activation that was specific to unaccusatives. Our findings indicate that the neural processing of unaccusative and transitive verbs is highly similar, and very different from the processing of unergative verbs. We discuss the consequences of these results for the linguistic analysis of movement phenomena.