Increased Posterior Cortical Recruitment Mediates Shift From Local to Global Processing in Children with Autism

Background:  Enhanced performance of individuals with autism on tasks such as the
Embedded Figures Test (EFT) and the Block Design Test (BDT) has been attributed to their
increased reliance on local details (Plaisted et al, 2003; Mottron et al, 2003). There are only a
few neuroimaging studies targeting global and local processing in autism (Damarla et al., 2010;
Liu et al., 2011; Ring et al., 1999), with main findings of increased posterior brain activation in
participants with autism. While these studies have focused on adults with autism, the main goal
of the present study is to probe the neural circuitry underlying the global and local processing in
children with autism.

Objectives:  The main objective of this fMRI study is to examine the neural bases of global and
local processing in children with autism.

Methods:  Eleven high-functioning children with autism (age range: 10-15 years) and thirteen
age-and-IQ-matched typical control participants took part in this fMRI study. The stimuli,
presented in an event-related design, consisted of larger geometric shapes make out of different
smaller geometric shapes. Participants were prompted to identify the bigger picture in some
trials (global condition) or alternatively to identify the smaller components of the bigger picture in
the remaining trials (local condition). The fMRI data collected from a Siemens 3.0T MRI scanner
were analyzed using Statistical Parametric Mapping (SPM8).

Results:  Analysis of behavioral data revealed intact task performance in participants with
autism with no significant group difference in accuracy (Control: Local-83%, Global-86%;
Autism: Local-79%, Global-77%) or latency (Control: Local-2606ms, Global-2648ms; Autism:
Local-2534ms, Global-2358ms). Within group brain responses suggest robust activation in
superior parietal and occipital areas in both autism and control groups during local and global
processing. Between group contrasts revealed significantly greater activation in autism in
bilateral precuneus, right middle temporal gyrus, and right lingual gyrus during global processing
(p<0.005, cluster size=90 mm3). Further analysis using parameter estimates also showed
increased recruitment of the precuneus in autism during global processing.

Conclusions:  A more expansive pattern of brain activation in global processing in autism may
imply the need for participants with autism to recruit more areas in order to overcome a potential
default local-oriented processing. It should be noted that the behavioral performance was intact,
but not superior, in participants with autism both in local and in global processing, perhaps
attributed to a local advantage manifested only in open tasks (Plaisted, 2001). Increased
activation in autism in the lingual gyrus and right middle temporal area is perhaps indicative of
more effort in global processing (Fink et al., 1996; Han et al., 2002; Seymour, 2008). In addition,
precuneus activation in autism suggests the shift in attention from local (default in autism) to
global shape (Himmelbach et al., 2009). Therefore, the shift from local to global processing in
autism may require additional effort at the neural and cognitive levels.