Measuring Cognitive Flexibility with the Flexible Item Selection Task: From fMRI Adaptation to Individual Connectome Mapping.

Cognitive flexibility, the ability to appropriately adjust behavior in a changing environment, has been challenging to operationalize and validate in cognitive neuroscience studies. Here, we investigate neural activation and directed functional connectivity underlying cognitive flexibility using an fMRI-adapted version of the Flexible Item Selection Task (FIST) in adults (n = 32, ages 19-46 years). The fMRI-adapted FIST was reliable, showed comparable performance to the computer-based version of the task, and produced robust activation in frontoparietal, anterior cingulate, insular, and subcortical regions. During flexibility trials, participants directly engaged the left inferior frontal junction, which influenced activity in other cortical and subcortical regions. The strength of intrinsic functional connectivity between select brain regions was related to individual differences in performance on the FIST, but there was also significant individual variability in functional network topography supporting cognitive flexibility. Taken together, these results suggest that the FIST is a valid measure of cognitive flexibility, which relies on computations within a broad corticosubcortical network driven by inferior frontal junction engagement.

The frontal aslant tract (FAT) and its role in speech, language and executive function.

In this review, we examine the structural connectivity of a recently-identified fiber pathway, the frontal aslant tract (FAT), and explore its function. We first review structural connectivity studies using tract-tracing methods in non-human primates, and diffusion-weighted imaging and electrostimulation in humans. These studies suggest a monosynaptic connection exists between the lateral inferior frontal gyrus and the pre-supplementary and supplementary motor areas of the medial superior frontal gyrus. This connection is termed the FAT. We then review research on the left FAT's putative role in supporting speech and language function, with particular focus on speech initiation, stuttering and verbal fluency. Next, we review research on the right FAT's putative role supporting executive function, namely inhibitory control and conflict monitoring for action. We summarize the extant body of empirical work by suggesting that the FAT plays a domain general role in the planning, timing, and coordination of sequential motor movements through the resolution of competition among potential motor plans. However, we also propose some domain specialization across the hemispheres. On the left hemisphere, the circuit is proposed to be specialized for speech actions. On the right hemisphere, the circuit is proposed to be specialized for general action control of the organism, especially in the visuo-spatial domain. We close the review with a discussion of the clinical significance of the FAT, and suggestions for further research on the pathway.

Neural development of networks for audiovisual speech comprehension.

Everyday conversation is both an auditory and a visual phenomenon. While visual speech information enhances comprehension for the listener, evidence suggests that the ability to benefit from this information improves with development. A number of brain regions have been implicated in audiovisual speech comprehension, but the extent to which the neurobiological substrate in the child compares to the adult is unknown. In particular, developmental differences in the network for audiovisual speech comprehension could manifest through the incorporation of additional brain regions, or through different patterns of effective connectivity. In the present study we used functional magnetic resonance imaging and structural equation modeling (SEM) to characterize the developmental changes in network interactions for audiovisual speech comprehension. The brain response was recorded while children 8- to 11-years-old and adults passively listened to stories under audiovisual (AV) and auditory-only (A) conditions. Results showed that in children and adults, AV comprehension activated the same fronto-temporo-parietal network of regions known for their contribution to speech production and perception. However, the SEM network analysis revealed age-related differences in the functional interactions among these regions. In particular, the influence of the posterior inferior frontal gyrus/ventral premotor cortex on supramarginal gyrus differed across age groups during AV, but not A speech. This functional pathway might be important for relating motor and sensory information used by the listener to identify speech sounds. Further, its development might reflect changes in the mechanisms that relate visual speech information to articulatory speech representations through experience producing and perceiving speech.

Co-speech gestures influence neural activity in brain regions associated with processing semantic information.

Everyday communication is accompanied by visual information from several sources, including co-speech gestures, which provide semantic information listeners use to help disambiguate the speaker's message. Using fMRI, we examined how gestures influence neural activity in brain regions associated with processing semantic information. The BOLD response was recorded while participants listened to stories under three audiovisual conditions and one auditory-only (speech alone) condition. In the first audiovisual condition, the storyteller produced gestures that naturally accompany speech. In the second, the storyteller made semantically unrelated hand movements. In the third, the storyteller kept her hands still. In addition to inferior parietal and posterior superior and middle temporal regions, bilateral posterior superior temporal sulcus and left anterior inferior frontal gyrus responded more strongly to speech when it was further accompanied by gesture, regardless of the semantic relation to speech. However, the right inferior frontal gyrus was sensitive to the semantic import of the hand movements, demonstrating more activity when hand movements were semantically unrelated to the accompanying speech. These findings show that perceiving hand movements during speech modulates the distributed pattern of neural activation involved in both biological motion perception and discourse comprehension, suggesting listeners attempt to find meaning, not only in the words speakers produce, but also in the hand movements that accompany speech.