The Neural Correlates of Semantic and Grammatical Encoding During Sentence Production in a Second Language: Evidence From an fMRI Study Using Structural Priming

Japanese English learners have difficulty speaking Double Object (DO; give B A) than Prepositional Object (PO; give A to B) structures which neural underpinning is unknown. In speaking, syntactic and phonological processing follow semantic encoding, conversion of non-verbal mental representation into a structure suitable for expression. To test whether DO difficulty lies in linguistic or prelinguistic process, we conducted functional magnetic resonance imaging. Thirty participants described cartoons using DO or PO, or simply named them. Greater reaction times and error rates indicated DO difficulty. DO compared with PO showed parieto-frontal activation including left inferior frontal gyrus, reflecting linguistic process. Psychological priming in PO produced immediately after DO and vice versa compared to after control, indicated shared process between PO and DO. Cross-structural neural repetition suppression was observed in occipito-parietal regions, overlapping the linguistic system in pre-SMA. Thus DO and PO share prelinguistic process, whereas linguistic process imposes overload in DO.

Layer-Specific Intracortical Amplification Shortens the Lifetime of Thalamocortical Repetition Suppression in Auditory Cortex

Neural adaptation in sensory cortex serves important sensory functions, and is altered by various neurophsychiatric diseases. Although adaptation is a widely studied phenomenon, much remains unknown about its underlying mechanisms on a cortical circuit level. Here, we investigated repetition suppression as fundamental aspect of adaptation by layer-specific current source density analyses of synaptic mass activities in primary auditory cortex of anesthetized Mongolian gerbils (Meriones unguiculatus). We disentangled different synaptic contributions to repetition suppression in different cortical layers, and separated thalamocortical from intracortical inputs by cortical silencing with GABAA-agonist muscimol. We systematically varied stimulus onset intervals and employed statistically robust model fitting based on bootstrapping to determine the full suppression kinetics of different synaptic responses in the steady state. Whereas thalamocortical input to granular and infragranular layers was governed by longer lasting repetition suppression, most likely reflecting depression of thalamocortical synapses, intracortical amplification in granular layers shortened the lifetime of suppression by re-enhancing granular responses mainly through synchronization of synaptic events. With increasing latency, the shorter lasting suppression kinetics observed in granular layers at early latencies (<100ms) passed on to deeper layers replacing the longer lasting infragranular suppression kinetics. Granular circuit dynamics can therefore actively shape neural adaptation across cortical layers.

Controlling precedence in sequential stimulus presentation with Euler tours

It is important to control for stimulus history in experiments probing responses to and similarity between sequentially presented stimuli. We present a method for stimulus order randomisation that guarantees identical precedence across stimuli. Generating sequences through sampling Euler tours allows for perfectly uniform stimulus history. This deconfounds the stimulus history from the present stimulus and maximises sensitivity to stimulus history effects including repetition suppression.

Repetition Probability Effects for Words Depend on Language Knowledge

The magnitude of repetition suppression (RS), measured by fMRI, is modulated by the probability of repetitions (P(rep)) for various sensory stimulus categories. It has been suggested that for visually presented simple letters this P(rep) effect depends on the prior practices of the participants with the stimuli. Here we tested further if previous experiences affect the neural mechanisms of RS, leading to the modulatory effects of stimulus P(rep), for more complex lexical stimuli as well. We measured the BOLD signal in the Visual Word Form Area (VWFA) of native Chinese and German participants and estimated the P(rep) effects for Chinese characters and German words. The results showed a significant P(rep) effect for stimuli of the mother tongue in both participant groups. Interestingly, Chinese participants, learning German as a second language, also showed a significant P(rep) modulation of RS for German words while the German participants who had no prior experiences with the Chinese characters showed no such effects. Our findings suggest that P(rep) effects on RS are manifest for visual word processing as well, but only for words of a language with which the participants have prior experiences. These results support further the idea that predictive processes, estimated by P(rep) modulations of RS, require prior experiences.

Suppression, Maintenance, and Surprise: Neuronal Correlates of Predictive Processing Specialization for Musical Rhythm

Auditory repetition suppression and omission activation are opposite neural phenomena and manifestations of principles of predictive processing. Repetition suppression describes the temporal decrease in neural activity when a stimulus is constant or repeated in an expected temporal fashion; omission activity is the transient increase in neural activity when a stimulus is temporarily and unexpectedly absent. The temporal, repetitive nature of musical rhythms is ideal for investigating these phenomena. During an fMRI session, 10 healthy participants underwent scanning while listening to musical rhythms with two levels of metric complexity, and with beat omissions with different positional complexity. Participants first listened to 16-s-long presentations of continuous rhythms, before listening to a longer continuous presentation with beat omissions quasi-randomly introduced. We found deactivation in bilateral superior temporal gyri during the repeated presentation of the normal, unaltered rhythmic stimulus, with more suppression of activity in the left hemisphere. Omission activation of bilateral middle temporal gyri was right lateralized. Persistent activity was found in areas including the supplementary motor area, caudate nucleus, anterior insula, frontal areas, and middle and posterior cingulate cortex, not overlapping with either listening, suppression, or omission activation. This suggests that the areas are perhaps specialized for working memory maintenance. We found no effect of metric complexity for either the normal presentation or omissions, but we found evidence for a small effect of omission position—at an uncorrected threshold—where omissions in the more metrical salient position, i.e., the first position in the bar, showed higher activation in anterior cingulate/medial superior frontal gyrus, compared to omissions in the less salient position, in line with the role of the anterior cingulate cortex for saliency detection. The results are consistent with findings in our previous studies on Parkinson’s disease, but are put into a bigger theoretical frameset.

Long term fMRI adaptation depends on adapter response in face-selective cortex

Repetition suppression (RS) reflects a neural attenuation during repeated stimulation. We used fMRI and the subsequent memory paradigm to test the predictive coding hypothesis for RS during visual memory processing by investigating the interaction between RS and differences due to memory in category-selective cortex (FFA, pSTS, PPA, and RSC). Fifty-six participants encoded face and house stimuli twice, followed by an immediate and delayed (48 h) recognition memory assessment. Linear Mixed Model analyses with repetition, subsequent recognition performance, and their interaction as fixed effects revealed that absolute RS during encoding interacts with probability of future remembrance in face-selective cortex. This effect was not observed for relative RS, i.e. when controlled for adapter-response. The findings also reveal an association between adapter response and RS, both for short and long term (48h) intervals, after controlling for the mathematical dependence between both measures. These combined findings are challenging for predictive coding models of visual memory and are more compatible with adapter-related and familiarity accounts.