Showing papers by "Roger B. H. Tootell published in 2008"

Perception of emotional expressions is independent of face selectivity in monkey inferior temporal cortex

Abstract: The ability to perceive and differentiate facial expressions is vital for social communication. Numerous functional MRI (fMRI) studies in humans have shown enhanced responses to faces with different emotional valence, in both the amygdala and the visual cortex. However, relatively few studies have examined how valence influences neural responses in monkeys, thereby limiting the ability to draw comparisons across species and thus understand the underlying neural mechanisms. Here we tested the effects of macaque facial expressions on neural activation within these two regions using fMRI in three awake, behaving monkeys. Monkeys maintained central fixation while blocks of different monkey facial expressions were presented. Four different facial expressions were tested: (i) neutral, (ii) aggressive (open-mouthed threat), (iii) fearful (fear grin), and (iv) submissive (lip smack). Our results confirmed that both the amygdala and the inferior temporal cortex in monkeys are modulated by facial expressions. As in human fMRI, fearful expressions evoked the greatest response in monkeys—even though fearful expressions are physically dissimilar in humans and macaques. Furthermore, we found that valence effects were not uniformly distributed over the inferior temporal cortex. Surprisingly, these valence maps were independent of two related functional maps: (i) the map of “face-selective” regions (faces versus non-face objects) and (ii) the map of “face-responsive” regions (faces versus scrambled images). Thus, the neural mechanisms underlying face perception and valence perception appear to be distinct.

fMRI mapping of a morphed continuum of 3D shapes within inferior temporal cortex

Abstract: Here, we mapped fMRI responses to incrementally changing shapes along a continuous 3D morph, ranging from a head (“face”) to a house (“place”). The response to each shape was mapped independently by using single-stimulus imaging, and stimulus shapes were equated for lower-level visual cues. We measured activity in 2-mm samples across human inferior temporal cortex from the fusiform face area (FFA) (apparently selective for faces) to the parahippocampal place area (PPA) (apparently selective for places), testing for (i) incremental changes in the topography of FFA and PPA (predicted by the continuous-mapping model) or (ii) little or no response to the intermediate morphed shapes (predicted by the category model). Neither result occurred; instead, we found approximately linearly graded changes in the response amplitudes to graded-shape changes, without changes in topography—similar to visual responses in different lower-tier cortical areas.

Organization of Human Visual Cortex

Abstract: Over the past three decades, the systematic exploration of the primate visual cortex has been a major target of neurobiological research. The visual cortex has been extensively studied in the macaque monkey, whose visual system is similar in many ways to that of humans. On the basis of anatomical, physiological, and behavioral information, ∼ 30 distinct visual cortical areas have been described in the macaque. Human visual cortex, largely terra incognita until the past decade, is now accessible by neuroimaging techniques, and these techniques have enabled neuroscientists to map the human visual areas with respect to their functional organization. This chapter gives a comprehensive overview of key discoveries relating to the human visual cortex.

Reply to Sterck and Goossens: Perception of facial expressions in rhesus macaques

Abstract: We thank Sterck and Goossens (1) for their comments. We all agree that the specific expressions tested (open-mouth threats, fear grins, and lip smacks) are key components in the behavioral repertoire of rhesus macaques. Our conclusions were that (i) facial expressions (relative to neutral faces) modulated neural activity within the visual cortex and …