Beyond the Simple "Face Cell": Response Modulation of Neurons in the Superior Temporal Sulcus to Saccadic Eye Movements

Human and non-human primates have evolved specialized abilities to distinguish among conspecifics' facial characteristics such as identity and facial expression. A cortical network in the temporal lobe of the monkey has been implicated in such specialized perception, though it is possible that additional factors could contribute to the responses of temporal lobe neurons. Objectives: In this study, we explore the influence of eye movements on neural responses in the temporal lobe. In addition we will determine whether neurons responsive to face stimuli are also saccade-modulated, and if so, whether modulation to both can occur simultaneously, while scanning face images. Materials and Methods: Awake macaques were presented with a set of clip-art objects or faces of monkeys displaying aggressive, neutral, and appeasing expressions while we recorded from neurons in the superior temporal sulcus (STS). Evoked responses to the images were evaluated, in addition to responses to saccades occurring prior to fixation onset (spontaneous saccades), at the time of central cue fixation (visually-guided saccades) and while an image was viewed (image-guided saccades). Results: We found identity-selective as well as expression-selective unit responses to the face stimuli within the upper bank STS, as well as overall preferences for faces or objects. The unit responses were typically consistent with fluctuations in the local field potential (LFP). Both unit and LFP responses showed peri-saccadic modulation, whether for spontaneous or visually-guided saccades. In addition to describing this general saccadic modulation, we will discuss the modulation of saccadic eye movements during stimulus response window (i.e.100-500 ms after image onset). Conclusion: The results of our study not only demonstrate neuronal selectivity for facial expressions and identity in the upper bank STS but also provide evidence that such neurons are influenced by eye movements. Saccadic modulation of face-selective neurons may be understood within the framework of embodied cognition