The influence of semantic associations on sentence production in schizophrenia: an fMRI study

Losing the chain of thought: A meta-analysis of functional neuroimaging studies using verbal tasks in schizophrenia

BACKGROUND

Disorganization symptoms are a main feature of schizophrenia, which include illogical and incoherent thinking, circumstantiality, tangentiality and loose associations. As these symptoms entail language deficits, several functional neuroimaging studies have been performed in schizophrenia using verbal tasks, producing somewhat heterogenous results. Hence, we performed a meta-analysis seeking to identify the most reliable neural alterations observed in schizophrenia patients during such tasks.

METHODS

Web of Sciences, PubMed, and EMBASE were searched for functional neuroimaging studies during verbal tasks (e.g. verbal fluency and semantic processing) in schizophrenia. Out of 795 screened articles, 33 were eligible for this meta-analysis. A coordinated-based meta-analysis was performed with the activation likelihood estimation (ALE) approach, using the cluster-level family-wise error (FWE) correction set at p < 0.05.

RESULTS

In schizophrenia, hyperactivations were observed in the left inferior frontal gyrus (IFG) and middle frontal gyrus (MFG) and hypoactivations were observed in the right IFG, the precentral gyrus and the left caudate nucleus. Another analysis pooling hyper- and hypoactivations revealed altered activations, firstly, in the left IFG and MFG, secondly, in the left precentral gyrus, IFG and insula, and, thirdly, in the left angular gyrus and precuneus. In the light of these results, not only classic language-related regions are abnormally activated during verbal tasks in schizophrenia, but also brain regions involved in executive functions, autobiographical memory and, unexpectedly, in motor functions. Further functional neuroimaging studies are needed to investigate the role of the striatum in linguistic sequencing in schizophrenia.

Mimicking effects of auditory verbal hallucinations on language production at the level of words, sentences and stories

Schizophrenia is characterised foremost by hallucinations, delusions and disorganised speech. Deficits in the internal speech monitor may contribute to the development of auditory-verbal hallucinations. This study investigates potential effects in the opposite direction: could the presence of auditory-verbal hallucinations have an effect on speech production? To this end, a recent mimicking/simulation approach was adopted for 40 healthy participants who perceived either white noise or hallucination-like speech recordings during different language production tasks with increasing demands: picture naming, verbal fluency with and without category switch, sentence production, and discourse. In line with reports about real schizophrenia cases in the literature, mimicking auditory-verbal hallucinations affected verbal fluency (switch condition) and sentence production (duration) in a different way than mere noise. These effects were not correlated, suggesting that hallucinations may even affect different levels of linguistic complexity in different ways. Anyway, in both cases (mimicked), auditory hallucination appear to contribute to the emergence of disordered speech. The mimicking/simulation paradigm may in future help to identify and disentangle the various factors contributing to disorganised speech in schizophrenia. They may also support the development and implementation of new protocols, e.g., in speech and language therapy in persons with schizophrenia in order to improve their communication skills despite the presence of auditory-verbal hallucinations.

Adaptation of a semantic picture-word interference paradigm for future language mapping with transcranial magnetic stimulation: A behavioural study

Neuro-navigated transcranial magnetic stimulation (TMS) helps to identify language-related cortical regions prior to brain tumour surgery. We adapted a semantic picture-word interference (PWI) paradigm from psycholinguistics to high-resolution TMS language mapping which prospectively can be used to specifically address the level of semantic processing. In PWI, pictures are presented along with distractor words which facilitate or inhibit the lexical access to the picture name. These modulatory effects of distractors can be annihilated in language-sensitive areas by the inhibitory effects of TMS on language processing. The rationale here is to observe the distractor effect without active stimulation and then to observe presumably its elimination by interference of the TMS stimulation. The special requirements to use PWI in this setting are (1) identifying word material for accelerating reliably naming latencies, choosing (2) the ideal presentation modality, and (3) the appropriate timing of distractor presentation. These are then controlled in real TMS language mapping. To adapt a semantic PWI naming paradigm for TMS application we employed 30 object-pictures in spoken German language. Part-whole associative semantic related or unrelated distractors were presented in two experiments including 15 healthy volunteers each, once auditorily and once visually. Data analysis across the entire stimulus set revealed a trend for facilitation in the visual condition, whereas no effects were observed for auditory distractors. In a sub-set, we found a significant facilitation effect for visual semantic distractors. Thus, with this study we provide a well-controlled item set for future studies implementing effective TMS language mapping applying visual semantic PWI.