Patients with amyotrophic lateral sclerosis (ALS), even without cognitive impairment, visually scan human faces, particularly faces displaying such negative expressions differently from people without ALS. These are the findings of a study published in Neurology.
Since oculomotor function is typically preserved until late-stage ALS, impaired emotion recognition previously has not been tied to motor impairment in this patient population. However, researchers hypothesized that motor processes that govern patients’ visual scanning are nevertheless disrupted. For the study, the researchers used video-based gaze tracking technology to determine whether the visual face scanning path differed between patients and healthy control participants.
A total of 45 patients with ALS, without cognitive impairment, were matched with 37 control participants by gender, age, and educational level. All participants gazed at images of faces displaying a variety of emotions as their eye movements were tracked. In addition, participants completed neuropsychological tests of cognition, function, and mood (depression and anxiety).
Based on the eye tracking measurements, the researchers calculated the number of visual fixations, and proportion of time spent, when gazing at particular facial target regions.
Compared with healthy controls participants, patients with ALS gazed more at nonsalient face regions such as cheeks, as opposed to the eyes or mouth, when viewing faces showing disgust or fear. That is, visual fixation times were longer for fearful (Mann-Whitney-U-test (U)=544.0, P =0.007) and disgusted (U=535.0, P =0.006) faces, and the number of fixations was greater for fear (U=606.5, P =0.035). Patients also spent less time looking at the eyes of disgusted faces (P =0.041). However, such between-group differences disappeared when participants examined happy or neutral faces. The groups also did not show a robust difference when looking at sad faces.
The degree of visuomotor abnormality was not associated with cognitive ability or symptom severity, as measured by the neuropsychological assessments. Therefore, the researchers hypothesized that the altered scan paths reflected impairment of top-down neural processes, specifically those that rely on prefrontal cortical areas recruited for face and emotion recognition. Furthermore, the researchers inferred, the observed visuomotor abnormalities may in fact underlie poor emotion recognition in ALS. Meanwhile, the lack of group difference in scanning happy or neutral faces could suggest that negative emotions require more neural resources than do positive ones.
The researchers acknowledged that they did not test directly whether participants’ altered visual scanning was associated with poorer emotion recognition, in real time. If future research confirms this, such data could help pave the way for new testing protocols.
“Overall, our findings further support the concept of eye tracking measures during (emotional) face exploration as a sensitive instrument to study subclinical neuropsychological deficits in ALS-patients,” the researchers wrote. “The present study formed the groundwork for future test batteries to assess neuropsychological performance in (physically) severely affected and ultimately ‘locked in’ patients.”
Nanning F, Braune K, Uttner I, Ludolph AC, Gorges M, Lulé D. Altered gaze control during emotional face exploration in patients with amyotrophic lateral sclerosis. Neurology. Published online March 30, 2023. doi:10.1212/WNL.0000000000207214