In Guy et al.’s article, “Cortical Source Analysis of the Face Sensitive N290 ERP Component in Infants at High Risk for Autism,” the researchers want to determine whether 12-month old infants who are diagnosed with autism spectrum disorder (ASD) experience atypical activity in the N290, which is an ERP component that is observed at 290 milliseconds. The N290 is responsible for face processing and works hand-in-hand with the P400 to help process faces. The P400 is an ERP component whose onset of stimulus occurs at 400 milliseconds and works closely with the N290 for face processing. Since the N290 and P400 help to contribute to face processing, this provides the foundation for the researchers to test these ERP components on infants who are at risk of developing ASD. ASD is a neurodevelopmental disorder that could be influenced by other genetic disorders, such as mutations on the X chromosome, also known as Fragile X Syndrome (FXS). FXS is a genetic condition that affects the X chromosome and has a high concordance rate (approximately 60%) with autism spectrum disorder. Therefore, the researchers used these individuals with FXS in order to determine any differences in the N290 ERP component. Additionally, another at-risk group of ASD––siblings with autism (ASIBs)––was tested and compared to those individuals with FXS and to typically developing (TD) infants to determine how much the responses differ in the N290 and P400 in FXS infants compared to ASIBs and TD infants. What the researchers found was that individuals with FXS experienced a greater response in the N290 compared to typically developing infants. Consequently, since the N290 and P400 work hand-in-hand to help process faces, FXS infants, who showed an increased amplitude in N290 responses, showed decreased response in the P400 ERP component. The greatest responses in the N290 corresponded to faces and similar objects, whereas the P400 corresponded to novelty preferences in FXS, since novel toys showed a greater response in the P400. For the ASIB individuals, there was not a distinct difference between the ASIB individuals and the TD infants, which indicates that FXS individuals were more responsive at the N290 and P400. Therefore, the presence of an object or a person did not have an effect on ASIB individuals in either the N290 or P400. What these differences mean are further discussed in the other article by Shepard et al. (2020).
In Shepard et al.’s article, “Neural and behavioral indices of face processing in siblings of children with autism spectrum disorder (ASD): A longitudinal study from infancy to mid-childhood,” the researchers conducted a longitudinal study that tested ASIB individuals from 7 months to 7 years of age to determine what behavioral and neural differences there are between children who are at high-risk of developing ASD and low-risk. This study helps to provide insight about the consequences that neurodevelopmental disorders such as ASD have on biological, psychological, and social factors. The researchers used ERP components to measure the responsiveness to different face and object stimuli. The ERP components of interest were the P1, N170, and P400. The N170 is a mature version of the infant N290, and this is due to experience allowing neurons to fire more quickly and efficiently. The P1, which is not present in infancy but develops later in childhood, is an ERP component which has a function similar to the P400, which helps aid in visual recognition and face processing. The researchers measured these different ERP components through the use of faces and objects (e.g. houses) and presented two images––one upright image and one inverted image. The purpose of this is to test the latency between the two groups at risk of ASD. What the researchers found was at age 7, high-risk children showed increased responses to inverted and upright faces/objects for the P1 and N170 components. What this means is that children at age 7 who are at high-risk of developing ASD are more likely to pay closer attention to objects and faces regardless of their orientation.. During childhood, as the N290 matures in the N170, face processing also begins to be lateralized. This means that face processing will slowly shift from being processed in both hemispheres to just the right hemisphere. Although high-risk children show a more intensified N170 component, this could mean atypical development, since as is seen with the low-risk children, there is a less intense response in the N170 component, indicating that high-risk children do not experience this right lateralization of face processing. This lack of lateralization in the right hemisphere has other implications, such as children’s reaction times to viewing the faces. What the researchers found was that high-risk boys experienced a slower reaction time to viewing faces and objects compared to lower-risk boys. This means that ASD could impact certain aspects that are sex-linked, in this case, face processing. When the researchers compared high-risk and low-risk girls, there was no difference in reaction times. With all of these components coming into play, the researchers are able to decipher these results that high-risk children with slower reaction times showed the least amount of right lateralization in the N170 component and this further explained the social impairments that are seen in high-risk children. Additionally, the researchers tested for noise disturbances and how high-risk versus low-risk children and how the N170 component could come into play. What the researchers found using a cortical source analysis is that high-risk children show greater activation in sensory areas (such as the parietal lobe) when processing faces as opposed to conventional face processing areas (fusiform gyrus and fusiform face area), which indicates that high-risk children show trouble when holistically processing faces and objects. Therefore, this explains why high-risk children show poor reaction times when processing faces and objects, since they focus their attention on the external sensory information. The same can be said for social settings, and high-risk children show poor social skills because of this shift in attention from facial cues to sensory cues.
Between both studies (Guy et al., 2022 & Shepard et al., 2020), the infant N290 is an important ERP component when it comes to face processing and both studies demonstrated how infants who are at risk of developing ASD show a difference in the N290. Guy et al. (2022) compared a group of 12-month infants with FXS, ASIBs, and TD infants, and what was shown was that FXS infants showed a greater N290 response to faces and objects compared to ASIBs and TD infants. Shepard et al. (2020) tied in this idea with the greater N290 response and how it can have negative outcomes later on in childhood. As was discussed, the increased intensity in the N290 can lead to an increased response in the N170 as brain maturation continues, and as Shepard et al. (2020) explained, this can contribution to atypical development in the sense of having a lack of right lateralization for face processing, poor social and communication skills, and an increased sensitivity to sensory cues, such as noise. Some of the differences between the two studies was that Guy et al. (2022) performed a cross-sectional study on 12-month old infants with a control group (TD infants) and then two groups of at-risk infants (ASIBs and FXS) and this can infer that FXS infants are at a higher risk of developing ASD and can reflect some of the results that could be in Shepard et al.’s article. Additionally, Shepard et al (2020) performed a longitudinal that tested low-risk and high-risk children for developing ASD; however, it was not clearly stated how the infants were classified as low-risk versus high-risk. Could this be due to a concordance rate with other comorbid disorders (e.g. FXS)? Nonetheless, I believe that these two articles work in harmony with one another and show the importance of the infant N290’s impact in face processing in at-risk infants for developing ASD and its further implications as these infants emerge into childhood.
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