Wednesday, November 5, 2014

Anorexia Nervosa as a Disorder of Perception

A key feature in anorexia nervosa is the disturbance in perception of the body.

This perceptual disturbance is encapsulated in criteria 3 from DSM-5:
 "Disturbance in the way in which one's body weight or shape is experienced, undue influence of body weight or shape evaluation, or denial of the seriousness of the current low weight"
 Santino Guadio from Italy and colleagues recently published a nice summary of the support for body image disturbance in anorexia nervosa. This study focused on research in the neuropsychology of anorexia nervosa.

This review is informative in outlining the components involved in sensory perception.

Here are the key findings from their review following their perception components outline.

Tactile perception
What it is: identifying touch stimuli and discriminating differences in stimuli
How it is tested: finger identification test, tactile estimation task (estimating distance between two tactile stimuli in different body sites
Findings in anorexia nervosa: Patients with anorexia nervosa perform poorly on identifying finger perception when blindfolded and two fingers are stimulated. Anorexia nervosa is also associated with overestimation of distance between stimulation sites over multiple body parts

Haptic perception
What it is: ability to identify shapes by touch when no visual input is available
How it is tested: Identifying figures and shapes with eyes closed using hands for sensory input
Findings in anorexia nervosa: Patients with anorexia nervosa perform more poorly than controls on correctly identify shape and form when unable to see an object. This deficit appears to be present during both active illness with weight loss and persists following weight restoration.

Propioception
What it is: identification of body and limb position in space
How it is tested: identification of right-left orientation, ability to place a rod in a vertical postion as body position is modified and no visual sensation is provided
Findings in anorexia nervosa: Patients with anorexia nervosa show impaired spatial orientation perception as well as deficits in correctly identifying right-left orientation.

Haptic-visual-proprioception integration:
What it is: Ability to estimate correct physical properties using both haptic and visual stimuli
How it is tested: Two objects of identical weight but difference size are presented for touch and sight input. Subjects estimate weight of two objects relative to each other
Findings in anorexia nervosa: Subjects with anorexia nervosa show reduction in size-weight performance and reduction integration of visual and haptic information.

Visual-tactile-proprioception integration:
What it is: use and integration of three sensory modalities, sight, touch and body position
How it is tested: rubber hand test where subjects estimate position of left index finger before and after visuotactile stimulations.
Findings in anorexia nervosa: Patients with anorexia nervosa show impairment in two components of visuo-tactile-propioception integration

Interoceptive perception:
What it is: ability to identify and process internal bodily sensations such as heartbeart, intestinal activity, hunger, pain
How it is tested: participants are asked to count their own heartbeats and this count is compared to actual heart rate. 
Findings in anorexia nervosa: Patients with anorexia nervosa show impaired perception of heartbeat compared to controls

The authors note they found a relatively few well-designed studies of perception in anorexia nervosa. 

Although the number of studies is small, this review supports a multi-modal impairment in perception in patients with anorexia nervosa compared to controls.

The authors note perception is known to be processed through the brain parietal lobe. They propose that parietal lobe dysfunction may impair perception in anorexia nervosa. This perceptual impairment may contribute to the body image disturbance found in the illness.

Look for an expansion of studies of perception in anorexia nervosa. Pairing neuropsychological perception studies with advanced brain imaging research techniques may be powerful strategy.

Readers with more interest in this topic can access the free full-text manuscript by clicking on the citation link below.

Figure of parietal lobe is from an iPad screenshot from the app Brain Tutor.

Follow the author on Twitter WRY999.

Gaudio S, Brooks SJ, & Riva G (2014). Nonvisual multisensory impairment of body perception in anorexia nervosa: a systematic review of neuropsychological studies. PloS one, 9 (10) PMID: 25303480

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