The human brain has an elaborate system to coordinate visual functions
and gaze direction. Gaze can be stabilized by active fixation provided
by a separate neural system (tectum and parietal cortex). Quick changes
of gaze direction (saccades) occur 3-5 times a second and are generated
either automatically or on the subjects voluntary decision. The
fixation system and the voluntary control system develop during
different time periods in life, with the latter being completed not
before the age of 15-20 years (Fischer et al., 1997. Brain Research).
Voluntary saccade generation is impaired after lesions of the frontal
cortical system (Guitton et al., 1985. Exp Brain Res. 58, 455) while
stable fixation is lost after tectal inactivation (Munoz and Wurtz,
1993. J. Neurophysiol. 70, 576). A subject with an impaired fixation
system is also impaired on an antisaccade task producing high %-numbers
of reflexive prosaccades. A subject with a selective
impairment of voluntary control may be able to suppress the reflexes
but is unable to look to the opposite side. Other subjects may be
impaired on both aspects of the antisaccade task.
Patients with schizophrenia (Matsue et al., 1994. Jpn J Psychiatry &
Neurology 48, 13), Alzheimer's disease (Currie et al., 1991. Arch
Neurol 48, 644), or advanced Parkinson's disease (Kitagawa et al.,
1994. Neurology 44, 2285), or lesions in the prefrontal cortex are
impaired on the antisaccade task, while patients with posterior
parietal lesions (Pierrot - Deseilligny et al., 1991. Brain 114, 1473)
or affective disorders (Fukushima et al., 1990. J Psychiatric Res. 24,
9) can perform this task sufficiently well. Abnormal numbers of express
saccades and significant changes in saccade latencies have been
described in different neurological and psychiatric disorders.
Corresponding normative data are available for healthy subjects of
different ages between 10 and 60 years.
The quality and the developmental state of fixation and automatic vs
voluntary saccade control can be accessed by reaction time measurements
and counting the number of direction errors as provided by EXE: an
extra diagnostic tools in the diagnosis of various abnormalities of the
central nervous system.
If you have any questions, please contact us!
Prof. Dr. B. Fischer