Refining the predictive pursuit endophenotype in schizophrenia.
BACKGROUND
To utilize fully a schizophrenia endophenotype in gene search and subsequent neurobiological studies, it is critical that the precise underlying physiologic deficit is identified. Abnormality in smooth pursuit eye movements is one of the endophenotypes of schizophrenia. The precise nature of the abnormality is unknown. Previous work has shown a reduced predictive pursuit response to a briefly masked (i.e., invisible) moving object in schizophrenia. However, the overt awareness of target removal can confound the measurement.


METHODS
This study employed a novel method that covertly stabilized the moving target image onto the fovea. The foveal stabilization was implemented after the target on a monitor had oscillated at least for one cycle and near the change of direction when the eye velocity momentarily reached zero. Thus, the subsequent pursuit eye movements were completely predictive and internally driven. Eye velocity during this foveally stabilized smooth pursuit was compared among schizophrenia patients (n = 45), their unaffected first-degree relatives (n = 42), and healthy comparison subjects (n = 22).


RESULTS
Schizophrenia patients and their unaffected relatives performed similarly and both had substantially reduced predictive pursuit acceleration and velocity under the foveally stabilized condition.


CONCLUSIONS
These findings show that inability to maintain internal representation of the target motion or integration of such information into a predictive response may be the specific brain deficit indexed by the smooth pursuit endophenotype in schizophrenia. Similar performance between patients and unaffected relatives suggests that the refined predictive pursuit measure may index a less complex genetic origin of the eye-tracking deficits in schizophrenia families.
Maryland Psychiatric Research Center, Lions Vision Center, Johns Hopkins School of Medicine, Baltimore, Maryland 21228, USA. ehong@mprc.umaryland.edu
L Elliot
LE
Hong
Kathleen A
KA
Turano
Hugh
H
O'Neill
Lei
L
Hao
Ikwunga
I
Wonodi
Robert P
RP
McMahon
Amie
A
Elliott
Gunvant K
GK
Thaker
D000328:Adult; D001288:Attention; D001364:Awareness; D010054:Brief Psychiatric Rating Scale; D005260:Female; D005820:Genetic Testing; D006801:Humans; D008297:Male; D008875:Middle Aged; D009039:Motion Perception; D010470:Perceptual Masking; D010641:Phenotype; D011698:Pursuit, Smooth / Q000235:genetics*; D012559:Schizophrenia / Q000175:diagnosis / Q000235:genetics*; D012565:Schizophrenic Psychology; D012569:Schizotypal Personality Disorder / Q000175:diagnosis / Q000235:genetics / Q000523:psychology