Neural correlates of transitive inference: An SDM meta-analysis on 32 fMRI studies

A Meta-Analysis of Functional Neuroimaging Studies of Ketamine Administration in Healthy Volunteers

Ketamine administration leads to a psychotomimetic state when taken in large bolus doses, making it a valid model of psychosis. Therefore, understanding ketamine's effects on brain functioning is particularly relevant. This meta-analysis focused on neuroimaging studies that examined ketamine-induced brain activation at rest and during a task. Included are 10 resting-state studies and 23 task-based studies, 9 of which were measuring executive functions. Using a stringent statistical threshold (TFCE <0.05), the results showed increased activity at rest in the dorsal anterior cingulate cortex (ACC), and increased activation of the right Heschl's gyrus during executive tasks, following ketamine administration. Uncorrected results showed increased activation at rest in the right (anterior) insula and the right-fusiform gyrus, as well as increased activation during executive tasks in the rostral ACC. Rest-state studies highlighted alterations in core hubs of the salience network, while task-based studies suggested an impact on task-irrelevant brain regions. Increased activation in the rostral ACC may indicate a failure to deactivate the default mode network during executive tasks following ketamine administration. The results are coherent with alterations found in schizophrenia, which confer external validity to the ketamine model of psychosis. Studies investigating the neural mechanisms of ketamine's antidepressant action are warranted.

Cross-frequency and inter-regional phase synchronization in explicit transitive inference

Explicit logical reasoning, like transitive inference, is a hallmark of human intelligence. This study investigated cortical oscillations and their interactions in transitive inference with EEG. Participants viewed premises describing abstract relations among items. They accurately recalled the relationship between old pairs of items, effectively inferred the relationship between new pairs of items, and discriminated between true and false relationships for new pairs. First, theta (4-7 Hz) and alpha oscillations (8-15 Hz) had distinct functional roles. Frontal theta oscillations distinguished between new and old pairs, reflecting the inference of new information. Parietal alpha oscillations changed with serial position and symbolic distance of the pairs, representing the underlying relational structure. Frontal alpha oscillations distinguished between true and false pairs, linking the new information with the underlying relational structure. Second, theta and alpha oscillations interacted through cross-frequency and inter-regional phase synchronization. Frontal theta-alpha 1:2 phase locking appeared to coordinate spectrally diverse neural activity, enhanced for new versus old pairs and true versus false pairs. Alpha-band frontal-parietal phase coherence appeared to coordinate anatomically distributed neural activity, enhanced for new versus old pairs and false versus true pairs. It suggests that cross-frequency and inter-regional phase synchronization among theta and alpha oscillations supports human transitive inference.

Meta-analysis of structural integrity of white matter and functional connectivity in developmental stuttering

Developmental stuttering is a speech disfluency disorder characterized by repetitions, prolongations, and blocks of speech. While a number of neuroimaging studies have identified alterations in localized brain activation during speaking in persons with stuttering (PWS), it is unclear whether neuroimaging evidence converges on alterations in structural integrity of white matter and functional connectivity (FC) among multiple regions involved in supporting fluent speech. In the present study, we conducted coordinate-based meta-analyses according to the PRISMA guidelines for available publications that studied fractional anisotropy (FA) using tract-based spatial statistics (TBSS) for structural integrity and the seed-based voxel-wise FC analyses. The search retrieved 11 publications for the TBSS FA studies, 29 seed-based FC datasets from 6 publications for the resting-state, and 29 datasets from 6 publications for the task-based studies. The meta-analysis of TBSS FA revealed that PWS exhibited FA reductions in the middle and posterior segments of the left superior longitudinal fasciculus. Furthermore, the analysis of resting-state FC demonstrated that PWS had reduced FC in the right supplementary motor area and inferior parietal cortex, whereas an increase in FC was observed in the left cerebellum crus I. Conversely, we observed increased FC for task-based FC in regions implicated in speech production or sequential movements, including the anterior cingulate cortex, posterior insula, and bilateral cerebellum crus I in PWS. Functional network characterization of the altered FCs revealed that the sets of reduced resting-state and increased task-based FCs were largely distinct, but the somatomotor and striatum/thalamus networks were foci of alterations in both conditions. These observations indicate that developmental stuttering is characterized by structural and functional alterations in multiple brain networks that support speech fluency or sequential motor processes, including cortico-cortical and subcortical connections.

The transitive inference task to study the neuronal correlates of memory-driven decision making: A monkey neurophysiology perspective

A vast amount of literature agrees that rank-ordered information as A>B>C>D>E>F is mentally represented in spatially organized schemas after learning. This organization significantly influences the process of decision-making, using the acquired premises, i.e. deciding if B is higher than D is equivalent to comparing their position in this space. The implementation of non-verbal versions of the transitive inference task has provided the basis for ascertaining that different animal species explore a mental space when deciding among hierarchically organized memories. In the present work, we reviewed several studies of transitive inference that highlighted this ability in animals and, consequently, the animal models developed to study the underlying cognitive processes and the main neural structures supporting this ability. Further, we present the literature investigating which are the underlying neuronal mechanisms. Then we discuss how non-human primates represent an excellent model for future studies, providing ideal resources for better understanding the neuronal correlates of decision-making through transitive inference tasks.