This past year we have continued to focus on a major part of long-term memory, termed semantic memory, that is composed of general information, such as facts, ideas, and the meaning of objects and words. We are particularly interested in characterizing the neural substrate mediating object and word meaning and its role in object perception. We are also interested in understanding how abstract knowledge, such as information about social interactions, is represented. Our studies have shown that information about salient properties of an object - such as what it looks like, how it moves, how it is used, and our affective reaction to it - are stored in our perceptual, action, and emotion systems. As a result, objects belonging to different categories such as animate entities (people, animals) and manmade manipulable objects (tools, utensils) are represented in partially distinct neural circuits. These distributed circuits also underpin our ability to understand more abstract events such as social and mechanical interactions (Martin 2016). One brain region that has been consistently associated with processing social information is the most anterior and superior region of the temporal lobe. Surprisingly, this brain region has also been associated with a completely different function - processing of written sentences. We noticed that many of these sentence processing studies used sentences that were nearly exclusively about social and/or social emotional situations. We reasoned that perhaps it was the content of these sentences, rather than sentence reading per se, that was driving activity in anterior temporal cortex. To evaluate this possibility we present word lists that differed in phrase length (single words, 3-word phrases, 6-word sentences) and semantic content (social-emotional, social, and inanimate objects). This allowed us to investigate if anterior temporal cortex responded to increasing phrase size (as a marker of sentence processing) with or without regard to a specific domain of concepts expressed in these sentences, i.e., social and/or social emotional content (Mellem et al., 2016). Our results showed that neural activity in anterior temporal cortex was modulated by word phrase length. However, this activity was strongly modulated by sentence content such that social and social-emotional concepts were preferred over material devoid of social content (i.e., limited to inanimate objects). Reading also induced content type effects in other brain regions associated with social processing including the amygdala and medial prefrontal cortex. In contrast, brain regions associated with processing information about inanimate objects responded most strongly to the non-social object phases and sentences. These findings extend our knowledge of the types of stimuli that social brain regions respond to (in this case simply reading about social interactions) and stress the importance of taking meaning into account when study the neural underpinnings of sentence processing. Progress has also been made on understanding the apparent category-related organization of ventral temporal cortex. One of the most robust and oft-replicated findings in cognitive neuroscience is that different regions of ventral temporal cortex respond preferentially to different categories of concrete objects. However, the determinants of this category-related organization remain to be fully established. We, and others, have recently proposed that a major contributing factor to this organization is privileged connectivity from each of these ventral temporal regions to other brain regions that store property information associated with that category. To test this hypothesis, we used fMRI to define category-related brain regions of interest (ROIs) in a large group of subjects (Stevens et al., 2017). We then used these ROIs in resting-state functional connectivity MRI analyses to explore functional connectivity among these regions. Our results demonstrate that distinct category-preferring regions of ventral temporal cortex show differentially stronger functional connectivity with other regions that have congruent category preference. Moreover, the strength of these connections varied with behavior. The better subjects performed on a specific cognitive task like word reading, the stronger the connectivity between regions responsible for visual word identification and language comprehension (Stevens et al., 2017). These findings support the claim that privileged connectivity with other cortical regions provides a powerful constraint on the category-related organization of this region of the brain.
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