Biomedical subjects

Stephen J Swithenby

Publications and source records attributed to Stephen J Swithenby.

5 recordsLinked to original sources

PubMed2006

Face and gaze processing in normally developing children: a magnetoencephalographic study.

Magnetoencephalography (MEG) was used to study the neural mechanisms underlying face and gaze processing in ten normally developing boys aged between 8 and 11 years and 12 adult males. The participants performed two tasks in which they had to decide whether images presented sequentially in pairs, depicted the same person or the same motorbike. In the first task, the participants saw pictures of faces in which the eyes were either open or shut and pictures of motorbikes. In the second task, participants saw pairs of faces with gaze averted to the left or right. In children there was no evidence of the face sensitive, low amplitude short latency (30-60 ms) activity seen previously in adults. A strong, midline posterior response at approximately 100 ms was observed in children, which was earlier and somewhat stronger to faces than to motorbikes; in adults the signal at this latency was weak. A clear face sensitive response was seen in adults at 135 ms, predominantly over the right inferior occipito-temporal regions. Although activity was observed in the children at the same latency, it was less prominent, not lateralized and was evoked similarly by faces and motorbikes. Averted gaze conditions evoked strong right-lateralized activity at approximately 245 ms in children only. These findings indicate that even in middle childhood the neural mechanisms underlying face processing are less specialized than in adults, with greater early activation of posterior occipital cortices and less specific activation of ventral occipito-temporal cortex.

Adult↗

PubMed2006

Face- and gaze-sensitive neural responses in children with autism: a magnetoencephalographic study.

Face and gaze processing were studied using magnetoencephalography in 10 children with autism and 10 normally developing children, aged between 7 and 12 years. The children performed two tasks in which they had to discriminate whether images of faces presented sequentially in pairs were identical. The images showed four different categories of gaze: direct gaze, eyes averted (left or right) and closed eyes but there was no instruction to focus on the direction of gaze. Images of motorbikes were used as control stimuli. Faces evoked strong activity over posterior brain regions at about 100 ms in both groups of children. A response at 140 ms to faces observed over extrastriate cortices, thought to be homologous to the N170 in adults, was weak and bilateral in both groups and somewhat weaker (approaching significance) in the children with autism than in the control children. The response to motorbikes differed between the groups at 100 and 140 ms. Averted eyes evoked a strong right lateralized component at 240 ms in the normally developing children that was weak in the clinical group. By contrast, direct gaze evoked a left lateralized component at 240 ms only in children with autism. The findings suggest that face and gaze processing in children with autism follows a trajectory somewhat similar to that seen in normal development but with subtle differences. There is also a possibility that other categories of object may be processed in an unusual way. The inter-relationships between these findings remain to be elucidated.

Autistic Disorder↗

PubMed2005

Abnormal activation of face processing systems at early and intermediate latency in individuals with autism spectrum disorder: a magnetoencephalographic study.

The neurological basis of developmental psychopathology in autism is a matter of intense debate. Magnetoencephalography (MEG) was used to study the neuronal responses associated with the processing of faces in 12 able adults with autism spectrum disorders (ASD), performing image categorization and image identification tasks. The neuromagnetic data were analysed using nonparametric time-series analysis and equivalent current dipole estimation. Comparison data were obtained from 22 normally developing adults. In individuals with ASD, the neural responses to images of faces, observed in right extrastriate cortices at approximately 145 ms after stimulus onset, were significantly weaker, less lateralized and less affected by stimulus repetition than in control subjects. Early latency (30-60 ms) responses to face images, over right anterior temporal regions, differed significantly between the two subject groups in the image identification task. No such difference was observed for images of mugs or meaningless geometrical patterns. These findings suggest that, during the course of development in individuals with ASD, the cortical activity associated with the processing of human faces assumes a different-from-normal localization in extrastriate brain regions. This abnormal localization may be associated with unusual, but nevertheless face-specific, fast processing pathways.

Adult↗

PubMed2004

The distributed neuronal systems supporting choice-making in real-life situations: differences between men and women when choosing groceries detected using magnetoencephalography.

In this work, magnetoencephalography was used to study the temporal dynamics of neural responses in 16 subjects (eight women, eight men) choosing among different day-to-day consumer items. At short latencies (< 150 ms), the evoked responses showed striate and extrastriate cortical activation common to the processing of general objects. At about 300 ms, women activated preferentially left posterior cortices, whereas men activated preferentially right temporal cortices. This may reflect sex/gender differences in cognitive strategies, emphasizing category-specific knowledge in women and spatial memories in men. At latencies greater than 500 ms, right parietal cortices were preferentially activated when previously bought or used items were chosen. In contrast, left inferior and right orbital cortices were preferentially activated when selecting less-known items. This may be interpreted as representing the neural correlates of decisions where the outcome is consistent with previous experience, and of choices which are 'difficult' in some sense. Analysis of coherent gamma-oscillations (20-45 Hz) revealed neural activity over left anterior and right dorsolateral cortices at long latency (> 1500 ms) when brand knowledge is low. This is consistent with the late binding of (brand) memories and evaluation of multiple sources of information when a choice is not obvious. gamma-Activity showed that women may activate larger neural networks when preference is high, suggesting that men and women exhibit different patterns of neural activity even though their overt performances are similar.

Adult↗

PubMed2003

Endogenous context for visual processing of human faces and other objects.

The human ability to quickly recognise faces and objects is an important skill. This skill may be facilitated by the prior existence of context-setting functional brain states. MEG was used to test the hypothesis that such states may be defined neurophysiologically. One type of state was identified by evaluating deterministic features in the dynamics of pre-stimulus brain activity in 10 individuals engaging in an object categorisation task. These states followed a statistical gamma-distribution similar to that seen in models of percept duration of competing stimuli. Both an early (42 ms) and a late (440 ms) response were only seen for face stimuli that were presented during states in which the MEG data displayed low determinism. A second type of state was identified by evaluating amplitudes of pre-stimulus brain activity. Between 140 and 150 ms, activity was highest for face as well as non-face stimuli presented during a low amplitude state. These findings suggest that detectable states may provide an endogenous context for object processing, independently of experimental parameters.

Adult↗