The structure of the cerebral cortex across adult life: age-related patterns of surface area, thickness, and gyrification.

Older adults exhibit global reductions in cortical surface area, but little is known about the regional patterns of reductions or how these relate to other measures of brain structure. This knowledge is critical to understanding the dynamic relationship between different macrostructural properties of the cortex throughout adult life. Here, cortical arealization, local gyrification index (LGI), and cortical thickness were measured vertex wise across the brain surface in 322 healthy adults (20-85 years), with the aims of 1) characterizing age patterns of the three separate cortical measures and 2) testing the age-independent relationships among cortical surface area, gyrification, and thickness. Surface area showed strong age-related decreases, particularly pronounced in dorsomedial prefrontal, lateral temporal, and fusiform cortices, independently of total white matter volume. LGI decreased with age independently of regional surface area, with strongest effects laterally, extending from the angular gyrus in all directions. As expected, regional surface area and LGI were positively related. However, both measures correlated negatively with thickness, indicating increasing local arealization and gyrification with decreasing cortical thickness. We suggest that this pattern of regional "cortical stretching" reflects the well-established phylogenetic principle of maximizing surface area and gyrification rather than increase thickness to facilitate brain connectivity and functional development.

The influence of context on hemispheric recruitment during metaphor processing.

Although the left hemisphere's prominence in language is well established, less emphasis has been placed on possible roles for the right hemisphere. Behavioral, patient, and neuroimaging research suggests that the right hemisphere may be involved in processing figurative language. Additionally, research has demonstrated that context can modify language processes and facilitate comprehension. Here we investigated how figurativeness and context influenced brain activation, with a specific interest in right hemisphere function. Previous work in our laboratory indicated that novel stimuli engaged right inferior frontal gyrus (IFG) and that both novel and familiar metaphors engaged right IFG and right temporal pole. The graded salience hypothesis proposes that context may lessen integration demands, increase the salience of metaphors, and thereby reduce right hemisphere recruitment for metaphors. In the present study, fMRI was used to investigate brain function, whereas participants read literal and metaphoric sentences that were preceded by either a congruent or an incongruent literal sentence. Consistent with prior research, all sentences engaged traditional left hemisphere regions. Differences between metaphors and literal sentences were observed, but only in the left hemisphere. In contrast, a main effect of congruence was found in the right IFG, the right temporal pole, and the dorsal medial pFC. Partially consistent with the graded salience hypothesis, our results highlight the strong influence of context on language, demonstrate the importance of the right hemisphere in discourse, and suggest that, in a wider discourse context, congruence has a greater influence on right hemisphere recruitment than figurativeness.

Strain-Level Analysis of Mother-to-Child Bacterial Transmission during the First Few Months of Life.

Bacterial community acquisition in the infant gut impacts immune education and disease susceptibility. We compared bacterial strains across and within families in a prospective birth cohort of 44 infants and their mothers, sampled longitudinally in the first months of each child's life. We identified mother-to-child bacterial transmission events and describe the incidence of family-specific antibiotic resistance genes. We observed two inheritance patterns across multiple species, where often the mother's dominant strain is transmitted to the child, but occasionally her secondary strains colonize the infant gut. In families where the secondary strain of B. uniformis was inherited, a starch utilization gene cluster that was absent in the mother's dominant strain was identified in the child, suggesting the selective advantage of a mother's secondary strain in the infant gut. Our findings reveal mother-to-child bacterial transmission events at high resolution and give insights into early colonization of the infant gut.

Written distractor words influence brain activity during overt picture naming.

Language production requires multiple stages of processing (e.g., semantic retrieval, lexical selection), each of which may involve distinct brain regions. Distractor words can be combined with picture naming to examine factors that influence language production. Phonologically-related distractors have been found to speed picture naming (facilitation), while slower response times and decreased accuracy (interference) generally occur when a distractor is categorically related to the target image. However, other types of semantically-related distractors have been reported to produce a facilitative effect (e.g., associative, part-whole). The different pattern of results for different types of semantically-related distractors raises the question about how the nature of the semantic relation influences the effect of the distractor. To explore the nature of these semantic effects further, we used functional MRI to examine the influence of four types of written distractors on brain activation during overt picture naming. Distractors began with the same sound, were categorically-related, part of the object to be named, or were unrelated to the picture. Phonologically-related trials elicited greater activation than both semantic conditions (categorically-related and part-whole) in left insula and bilateral parietal cortex, regions that have been attributed to phonological aspects of production and encoding, respectively. Semantic conditions elicited greater activation than phonological trials in left posterior MTG, a region that has been linked to concept retrieval and semantic integration. Overall, the two semantic conditions did not differ substantially in their functional activation which suggests a similarity in the semantic demands and lexical competition across these two conditions.

The influence of sentence novelty and figurativeness on brain activity.

The predominance of the left hemisphere in language comprehension and production is well established. More recently, the right hemisphere's contribution to language has been examined. Clinical, behavioral, and neuroimaging research support the right hemisphere's involvement in metaphor processing. But, there is disagreement about whether metaphors, in and of themselves, engage the right hemisphere or if other factors that vary between metaphors and literal language elicit right hemisphere engagement. It is important to disambiguate these issues to improve our basic knowledge of figurative language processing, to more precisely define how the right hemisphere supports language, and to facilitate our ability to understand and treat language impairments. Here we investigated the role of the right hemisphere in language comprehension with functional magnetic resonance imaging (fMRI) by manipulating familiarity in both literal and metaphoric sentences. In an event-related design, participants viewed English sentences that appeared every 4.5-9s, and to which they made a pleasantness judgment. All sentences elicited activation in traditional language brain regions including left inferior frontal gyrus, left anterior inferior temporal and left posterior middle temporal gyri. Overall, metaphors and novel stimuli elicited activation in bilateral inferior frontal gyri and left temporal regions. Additionally, metaphors elicited greater activation than literal sentences in right temporal pole. Although our results are partially consistent with the graded salience hypothesis and the coarse coding hypothesis, the right hemisphere's sensitivity to familiar metaphors suggests that right hemisphere recruitment is most influenced by semantic integration demands.