Social Processing and Neural Plasticity

National Institute Of Mental Health

Investigators

Linked publications, trials & patents

Abstract

Individuals vary in their social skills. This is because the core operations of social perception, memory, abstraction, and behavior derive from specialized brain circuits that are shaped through abundant experience during childhood and beyond. These circuits can, in some cases, dissociate from other parts of the brain serving similar functions. For example, damage to very specific parts of the temporal lobe can lead to the inability to recognize individual faces while not affecting the recognition of other objects. Damage in other areas can leave subjects with a difficulty in recognizing facial expression, voice intonation, or even prompt them to believe that their spouse is an impostor. Understanding this specialization at a neural level has made steady progress, since the discovery approximately 50 years ago that individual neurons respond selectively to faces, and sometimes to individual faces. Following the addition of functional magnetic resonance imaging (fMRI), the field of social neuroscience has greatly advanced, and much has been learned about the circuits underlying social perception. Importantly, this research has a direct bearing on a wide range of patients, as social perceptual deficits are a hallmark of many psychiatric illnesses. A key element of social vision is its adaptability. In our laboratory, we employ methods that allow us to track neural activity patterns over time, including days, weeks, and even months. This set of tools, which includes functional magnetic resonance imaging (fMRI), single-cell recordings, and optical recordings, allows us to study how visual perceptual learning of social stimuli is expressed in the brain. We have focused much of this work on face patches, which are small, circumscribed regions of the temporal and prefrontal cortex showing greater fMRI responses to faces than to other categories of stimuli. The longitudinal nature of our studies allows us to investigate plasticity over multiple time scales. This research has been further aided by our development of an avatar face stimulus, whose animation, facial expressions, and environmental context is under complete experimental control. This stimulus toolbox has been of great use for systematically studying the factors that determine neural firing, for example in the context of the geometry of natural vision. In the past year, we have published papers related to important aspects of face perception. For example, we have provided evidence that the recognition of facial identity utilizes learned, internal representation of the average face (Koyano et al, 2021). This normative stimulus shapes the responses of neurons across face patches, highlighting the distinctive, and hence recognizable, facial features. The brains use of norms for face recognition was originally hypothesized based on psychophysical studies. Our demonstration of a clear neural representation of the average face within the face patch system bolsters this view and suggests a more general mode by which the brain gathers and stores information through its natural experience. In a different study, which is complete and now nearing submission, we have taken an entirely different approach to understanding the determinants of neural responses to faces. In this study, we investigated critical facial elements for driving neurons in different face patches. In this study, facial elements are randomly intermixed on different images, for example with the eyes from one individual presented randomly with the mouths, heads, and bodies from many other individuals. One striking result from this combinatorial approach has been the extent to which a very small region of a given face can determine the neuron's response, and the extent to which responses to this important feature are robust to major changes to the scene. For example, neurons responding selectively to one set of eyes often continue to respond to those eyes even when they are placed within a different face, which is attached to a different body and placed in a different scene. The local domination of such features was surprising, particularly as they were measured from the same neural populations as the norm-based coding findings mentioned above. In a third study (Khandhadia et al, 2021), we investigated whether auditory stimuli are associated with visual stimuli in face patch neurons. In that study, we found that two anterior face patches responded very differently to the vocal track being added to the corresponding animated face. In one area (face patch AM), commonly held to be critical for face recognition, the acoustic content had no influence whatsoever on the visual responses. However, in another area (face patch AF), most cells were significantly influenced by the acoustic content, so long as it matched the visual content. This study demonstrate the previously unknown integration of sensory social signals within the face patch system. Finally, analyses are presently underway to use Ca++ fluorescence imaging to study cellular responses in face patches. Similar to the microelectrode recordings, these recordings also permit longitudinal tracking over weeks and months. Thus, our Ca++ fluorescence work will also be used to investigate whether neurons in face selective areas modify their response profiles as the subjects learn new faces.