Date of Award
Recognizing other individuals is a key social aspect of our everyday lives. To recognize a familiar individual, we must establish a link between sensory inputs and a representation of that individual held in memory. In primates, faces play a particularly important role on the sensory side of this process, which is reflected in an extensive network of face-selective areas along the inferior temporal lobe. However, where and how memory is re-activated during face perception remains unclear. Using functional magnetic resonance imaging (fMRI), we measured whole brain activity in macaques while they were watching pictures of other monkey faces that were either long-term acquaintances, visually familiar, or totally unfamiliar. In comparison to unfamiliar faces, the entire face-processing network showed increased activity in response to familiar faces of long-time personal acquaintances. In contrast, faces that were only visually familiar elicited less activity than totally unfamiliar faces in most face-selective areas. The face-processing network thus distinguished personally familiar faces from visually familiar faces. Personally familiar faces also prompted the activation of two previously unknown face-selective areas in the temporal lobe. One area was located in the perirhinal cortex (PR), which has been associated with declarative memory, and the other area was embedded in the temporal pole (TP), a region previously associated with social knowledge. These two novel face areas showed a non-linear response as blurred faces became gradually visible, rapidly becoming active when the faces of personal acquaintances became recognizable. Thus, mimicking the perception of a face approaching us, this paradigm revealed a neural correlate of the ‘aha!’ recognition moment in face areas TP and PR. As a first step towards advancing our understanding of the neuronal processing of individual recognition, our fMRI experiments identified two novel face areas specifically involved in recognizing familiar faces. However, the hemodynamic response cannot directly assess neurophysiological properties. Using fMRI-guided electrophysiology, we investigated the responses of neurons within the novel face area TP in awake monkeys, and we provided the first systematic evidence of cells selective for familiar faces. A high fraction of neurons in face area TP were selective for familiar monkey faces, and unfamiliar faces that were physically similar failed to elicit the same neural responses. Importantly, neurons in face area AM, which is thought to compute facial identity at the top of the face perception hierarchy, were not modulated by familiarity. Within TP, neurons also responded to monkey bodies, and to monkey vocalizations. Maximum activity was elicited by the joint observation of faces and bodies, and audiovisual interactions were evident in some TP neurons. Together, these results reveal neuronal processes underlying memory re-activation during face perception and generate hypotheses for testing how individual recognition is achieved through different modalities, thus advancing our understanding into how unique representations of familiar individuals are developed at the neural level.
Landi, Sofia Mariana, "From Face Perception to Individual Recognition: The Missing Link" (2019). Student Theses and Dissertations. 528.