Talk:Autonomous voice communication

Increased blood flow in Broca’s area during auditory hallucinations in schizophrenia

"The exclusively left-hemispheric location of the regions loading heavily on the first principal component suggests the involvement of language areas. The critical role of Broca’s area in this respect is well known, and PET studies have shown that the left temporal contribution to language functions is not restricted to Wernicke’s area, but extends to regions in the middle temporal gyrus21,22 and medial temporal lobe.23.24 The anterior cingulate cortex has also been activated in PET studies of language tasks, although this may reflect a role in the selection or initiation of movements (including speech), rather than a function specific to language itself.2s27 Since these areas are anatomically interconnected,28 a cautious interpretation of the data is that the generation of auditory hallucinations is associated with increased activity in a network of cortical language areas."^[1]

Reduced anterior superior temporal gyrus volumes were found to correlate with reports of increased severity of hallucinatory experience

"However, symptom severity, as indexed by the SAPS “global rating of hallucinations” score, was significantly correlated with larger reductions of the left superior temporal gyral region only, and the magnitude of the relationship was increased when noncurrent hallucinators were excluded (rs 5 .51). In other words, reduced anterior superior temporal gyrus volumes were found to correlate with reports of increased severity of hallucinatory experience across all the subjects with a past history of hallucinations. Hence, the findings support an integral role of the superior temporal gyrus in the pathogenesis of hallucinations in schizophrenia, and are consistent with a model postulating that the dysfunction underlying the production of auditory hallucinations affects similar brain regions subserving language processing. Moreover, the neuroanatomic findings suggest that the temporal lobe volume reductions observed may constitute a trait, as opposed to a state, marker of hallucinations, as it is unlikely that structural measures vary with symptom change. In other words, the observed structural disorder may be enduring and therefore, may correspond to a predisposition toward auditory hallucinations in schizophrenia."^[2]

Additional findings of Broca area and temporal involvement

"Our results point toward reduced connectivity in the frontotemporal language-processing network in schizophrenia patients with AVHs. More specifically, during inner speech, Broca’s area receives reduced input both from Wernicke’s area and from its contralateral homolog in patients with AVH (illustrated in figure 3). Our findings thus lend further support to the frontotemporal disconnectivity hypothesis of AVH and go beyond that by suggesting directionality. The findings also show that the presence of AVH may be linked to an increased deficit that is present to a lesser degree in those with psychosis, but without current AVH.

Our finding of impaired effective connectivity from other nodes in the speech-processing network (such as Wernicke’s region) to Broca’s region is in agreement with theories of hallucinations2,29,30 that consider that reduced information flow to Broca’s area could prime increased top-down efforts from Broca’s area that are less constrained by perceptual information. According to these theories, top-down connections modulate or sensitize sensory regions through a balance between top-down excitation and inhibition, but they cannot activate the sensory regions under normal conditions. If these top-down signals become tonically hyperactive during a mental disorder, the top-down expectations can give rise to conscious experiences in the absence of bottom-up inputs. A reduced information flow from the speech perception area in the left TPJ implies a loss of feedback to Broca’s area."^[3]

"The results of this study show that areas in the left frontal and temporal lobe that have been implicated in the phonological analysis of spoken words are also activated during the generation and phonological analysis of imagined speech. This was accomplished with the use of a novel task that allowed the neural assessment of auditory--verbal imagery (internally generating and ‘perceiving’ imagined speech) in a behaviorally controlled design. Conditions were compared in which the subjects (i) actually heard spoken words or (ii) imagined hearing spoken words, and subsequently discriminated between weak-initial words and strong-initial words (metrical stress evaluation). Extensive activation was observed in language production areas in the left hemisphere: SMA, inferior frontal gyrus (Broca’s area) and insula. These regions have typically been shown to be activated also in tasks of silent verbal fluency (Cuenod et al., 1995; Ojemann et al., 1998; Lurito et al., 2000), and silent reading of words and pseudowords (Hagoort et al., 1999). Consistent with previous language-related studies on phoneme monitoring, phoneme/syllable counting and word rhyming (for a review, Poldrack et al., 1999), it is of interest to note the implication of the inferior frontal gyrus in phonological processing and not merely speech production (Wise et al., 1999)."^[4]

Self or reality monitoring regions of the brain are involved

"The most popular cognitive theory of AVHs is arguably that many are the result of internal cognitive events, such as inner speech, being misattributed to an external or alien source (Waters et al., 2012a). Various models have suggested that this could be due to a specific deficit in the monitoring of one's own actions, known as self-monitoring (Frith, 1992), and/or due to a bias towards labelling internal mental events as externally produced under conditions of ambiguity, known as a bias in reality monitoring (Bentall and Slade, 1985). Evidence from neuroimaging suggests that monitoring of one's own speech, overt or covert, is related to activity in auditory cortical regions such as the lateral temporal lobe, including the superior temporal gyri (STG), a brain area that includes both primary and secondary auditory cortices (Allen et al., 2007; McGuire et al., 1996a). This corresponds well to ‘symptom-capture’ studies of AVHs, in which similar areas are often implicated (Allen et al., 2008). rTMS treatment is usually targeted at the left temporoparietal junction (TPJ), an area adjacent to, and with high levels of connectivity to, primary and secondary auditory cortex (Kindler et al., 2013). Therefore, it is possible that neurostimulation treatment affects brain regions involved in verbal self- or reality monitoring."^[5]

References