Facial Processing Development in Typical and Atypical Infants

In developmental cognitive neuroscience, it is essential to have a strong grasp on how the brain typically develops as humans age. Knowing this information allows for a better understanding of individuals who suffer from developmental disorders such as Autism Spectrum Disorder (ASD) by comparing them to their typically developing counterparts. These comparisons could allow for researchers and medical professionals to potentially identify the early markers of such disorders, and in turn, create preventative measures that could be implemented to reduce the severity of symptoms.

From the study titled, “Face-sensitive brain responses in the first year of life” by Conte, Richards, Guy, Xie, and Roberts (2020), researchers were attempting to better understand how neural areas responsible for facial processing and non-facial processing develop during the first few years of life. In conjunction with this primary goal, they had also sought to localize the source of these cortical responses and monitor their changes across the first year of life. In order to achieve these goals, Conte et al. (2017), utilized electroencephalogram (EEG), specifically event-related potentials (ERPs) in response to visual stimuli that were measured whilst the EEG was used on the participants. This study consisted of participants that were either 4.5, 6, 8, or 12 months old. These infants were then shown either pictures of faces or pictures of objects while connected to an EEG, thus, allowing for the time locking of stimulus presentation to the ERPs. Two different attentional variations of these trials were run, consisting of the presence of infant attention or without infant attention. Four different ERPs were looked at in this study and consisted of: the P1, N290, P400, and the Nc. In terms of the P1, results had shown that generally, there were higher amplitude responses for faces than objects. This was consistent during the attentional trials as well. There was, however, no difference in amplitudes as age progressed. Similarly, the N290 had also shown heightened amplitude responses for faces than objects, yet this ERP amplitude did increase with age. The P400 was not associated with a preference for faces nor object processing and showed a linear increase in amplitude with age. In terms of the Nc component, there was a greater amplitude for faces during attentional trials at 6 months and older. This was the inverse for infants younger than 4.5 months old.

Conte et al. (2017), then attempted to localize the sources of these ERPs and identified that the N290 was primarily located in the middle fusiform gyrus. The P400 did not seem to have any localization in the regions of interest the researchers were looking at. The last area localized was the Nc, which was found to have been localized in the para-hippocampal gyrus.

The study conducted by Shephard et al. (2020), had also utilized ERPs to analyze facial processing in infants, however, those with risks of developing ASD were of interest. This study was specifically a longitudinal one, where two different groups of participants existed. The first group consisted of infants that were at high-risk for ASD (HR) due to their older sibling being previously diagnosed with ASD, and the last group consisted of low-risk (LR) infants. Infants underwent EEG and ERP testing similarly to Conte et al. (2020), however, the ERPs of interest were the P1 and N170. These participants were studied once at 7-months-old and then once again when they were 7 years old. During the 7-month-old testing period, the participants completed a viewing task where they were shown images of female faces and audio of female voices played whilst EEG was being recorded. Additionally, the amount of attention to facial stimuli was recorded, and participants completed a Face Pop-Out task where four total images were presented at a time, and one of the images always consisted of a scrambled face. The total time spent looking at the faces compared to the other pictures was then calculated. These paradigms were then run once again when participants had reached 7 years of age. Ultimately, Shephard et al. (2020), had found that the HR infants had atypical N170 amplitudes that were significantly higher than the LR infants. The N170 was found to be less right-lateralized than normal and was correlated with increased social deficits at 7 years old compared to the LR group. The P1 ERP was also found to be atypical in the HR groups, where there was the presence of shorter latencies. Similar to the N170 abnormality being tied to reduced social communication skills, the low latency P1 readings were associated with the same thing when HR infants were studied again at 7 years old. Surprisingly, the researchers did not find any significant link between attention to face stimuli and the onset of ASD symptoms at 7 years old. There was a nonsignificant trend, however, that suggested that less attention on facial stimuli during infancy was related to an increase in ASD symptoms at 7 years old, but this effect did not reach significance.

The findings of Conte et al. (2020) and Shephard et al. (2020) go hand in hand with one another. On one end of the spectrum, there is developmental evidence for typical facial processing in infants which was shown to be dynamic in nature during the first year of life. On the other end, the research conducted by Shephard et al. (2020) tracked the long-term development of high-risk ASD infants and their ERP readings once again showing this aberration from typical low-risk participants. When combined, the findings of these two experiments could be juxtaposed together to increase the ability for healthcare professionals to identify the emergence of mental disorders such as ASD. By using a measure like the ERP which is incredibly useful in studying infants, unlike fMRI, other facets of ASD could be monitored rather than just facial processing, such as the typical aversion to loud auditorial stimuli. More research does need to be done in the ages between the first year of life and beyond. With the varying levels and timings of brain maturation that occurs throughout the life span, these findings can be expanded on by monitoring individuals more frequently in longitudinal studies, and even go further into adulthood. This would allow for more comparisons to be implemented in older individuals afflicted with these disorders, compared to those that are typically developing.

References

Conte, S., Richards, J. E., Guy, M. W., Xie, W., & Roberts, J. E. (2020). Face-sensitive brain responses in the first year of life. NeuroImage, 211, 116602. https://doi.org/10.1016/j.neuroimage.2020.116602

Shephard, E., Milosavljevic, B., Mason, L., Elsabbagh, M., Tye, C., Gliga, T., Jones, E. JH., Charman, T., Johnson, M. H., Baron-Cohen, S., Bedford, R., Bolton, P., Chandler, S., Fernandes, J., Garwood, H., Hudry, K., Pasco, G., Pickles, A., Tucker, L., & Volein, A. (2020). Neural and behavioural indices of face processing in siblings of children with autism spectrum disorder (ASD): A longitudinal study from infancy to mid-childhood. Cortex, 127, 162–179. https://doi.org/10.1016/j.cortex.2020.02.008