ERP Components Revealing Brain Areas Associated with Face Recognition in infants

     Face recognition is an important ability that allows a person to have social interaction and communication with people. We often read about people who cannot recognize faces but possess a functional sensory system (for example, the eye). Where people argue that face recognition is an essential factor for adults, we see that infants equally need the ability of face recognition. With the growing advancements in science and technology, researchers can detect the areas associated with face recognition not only in monkeys but also in humans. It was found earlier that the fusiform face area (FFA) located in the brain's temporal lobe is a crucial structure for face recognition.

    Dr. Maggie Guy, with her colleagues, researched on face sensitives brain responses in infants in the first year of life. She conducted her study on 12-month-old infants. Twenty-one participants belonged to the ASIB group. These were the siblings of the infants with autism. Fifteen infants belonged to the FXS group. These infants had Fragile X Chromosome disorder. Twenty-one infants with a low risk of developing ASD were the control group. . Children were presented with the visual stimuli consisting of their mother’s face, stranger’s face, favorite toy, and novel toy. ERP method was utilized to study face processing. The research team measured the ERP components (i.e., P1, N290, P400, Nc) amplitudes with stimuli presented, but their main focus was on the N290 ERP component. Across all the participants, the response rate was greater to faces than to toys. The source of the P400 and Nc was the posterior cingulate gyrus and prefrontal cortex. They observed that P1 reflects the activation of the occipital face area, and the fusiform gyrus was the source of the N290. They did not observe significant responses in P400 ERP, suggesting that it is not broadly associated with face processing and face recognition. However, the amplitude was more marked in P400 when the objects were shown toys rather than faces. Dr. Guy et al. found out that the Nc component responded to both faces and objects and was also associated with attention. N290 showed greater amplitudes across the experimental groups. The responses were greater to faces than to objects. The infants with FXS were the only ones that were able to distinguish between familiar and novel stimuli. MRI was required to examine the regions of activations relevant to face processing. However, when some parents refused to do the MRIs of their children, Guy et al. came up with the idea of IBIS head models. They found out the N290 had a significant peak in amplitude as compared to the other ERP components. They saw greater activation in the middle fusiform gyrus and nearby ROIs. They also noticed the activity in the fusiform face area, parahippocampal gyrus, anterior fusiform gyrus, and some activity in the lingual gyrus. Previous studies showed the N170 is a face-sensitive ERP component in adults.

           In the article, "Neural correlates of facial emotion processing in infancy," Wanze Xie and colleagues used ERP measures and cortical analysis to investigate the effects of emotion on the  ERP components associated with face recognition. 7 and 12 months infants participated in the study. Images of females expressing happy, angry, and fearful emotions were presented to the infants as visual stimuli. EEG technique was used to record their brain activity. They concluded that N290 had a more significant response to the fearful emotion. This suggests that the image was quickly processed in the infants' brains to avoid danger. The N290 response to fearful emotion was associated with the right Occipitotemporal lobe. Adults also show activation in the same region when viewing alarming images that suggest that N290 is developed into N170 with age. On the contrary, P400 and Pc showed greater responses toward the angry faces. They explained that this might be because the expressions in angry faces were more discomforting than the fearful faces. They observed cortical activation in the posterior cingulate gyrus when infants looked at the angry images, which tells that the region is the source location for Nc/P400. They concluded that the infants in their first year of life have the ability to distinguish between angry and fearful faces. The FFA (fusiform face area) plays an essential role in an infant's emotional processing. They also suggested that the posterior cingulate gyrus also plays an important role in an infant's emotion processing.

     The two studies explained above are related to each other. Both the studies looked at the response amplitude of P1, N290, P400, and Nc as associated with facial recognition. Where Xie and colleagues studied the emotional aspect of infants' face processing, Dr. Guy and her team went a little further and studied face processing in infants with a high risk of developing autism. Both the studies were consistent with higher responses of the N290 ERP component in infants. Both studies were able to find that N170 in adults develops from the N290. Both studies' result of source localization for each ERP component that was studied was consistent. Both the studies were not able to find the separate source locations for Nc and P400. In Dr. Guy's experiment, they did not observe amplitude in P400 in response to faces and objects. On the other hand, Xie et al. successfully observed P400 amplitude when participants were subjected to the angry images. Both the studies suggested that further researches should be conducted to investigate the response of ERP components to other stimuli such as orientation. The finding from both studies can be helpful for future studies. Dr. Guy's analysis can help the medical field in the treatment of infants with Autisms. The MRI studies showed the region that was less active in ASIBs that could help the medical field find ways to improve the activity of those brain regions. On the other hand, Xie et al. showed that different brain regions respond to different facial expressions and the response of ERP components was also different. This could help future studies learn more about ERP components and find if the same ERP components are functional in infant monkeys.

References 

Conte, Stefania, et al. “Face-Sensitive Brain Responses in the First Year of Life.” NeuroImage, vol. 211, 2020, p. 116602., https://doi.org/10.1016/j.neuroimage.2020.116602. 

Xie, Wanze, et al. “Neural Correlates of Facial Emotion Processing in Infancy.” Developmental Science, vol. 22, no. 3, 2018, https://doi.org/10.1111/desc.12758.