The purpose of the present study was to compare and contrast
behavioral performance on three different tasks of spatial
cognition during unilateral and bilateral reversible deactivation
of posterior parietal cortex. Specifically, we examined posterior
middle suprasylvian (pMS) sulcal cortex in adult cats during
temporary and reversible cooling deactivation. In Task 1, the
cats oriented to a high-contrast, black visual stimulus
moved into the visual field periphery. In Task 2, the
cats oriented to a static light-emitting diode (LED).
Task 3 examined the cats' ability to determine whether
a black-and-white checkered, landmark box was closer
to the right or left side of the testing apparatus. Following
training on all tasks, cryoloops were implanted bilaterally
within the pMS sulcus. Unilateral deactivation of pMS sulcal
cortex resulted in virtually no responses to either moved
or static stimuli and virtually no responses to landmarks
presented in the contralateral hemifield, and a profound
contralateral hemifield neglect was induced. Responses to stimuli
and landmarks presented in the ipsilateral hemifield were
unimpaired. Additive, bilateral cooling of the homotopic region
in the contralateral hemisphere, but not an adjacent region,
resulted in reversal of the initial hemineglect for the
moved stimulus, yet induced a complete failure to orient
to peripheral static LED stimuli. Bilateral cooling
also reversed the contralateral neglect of the landmark,
but then cats could not accurately determine position of the
landmark anywhere in the visual field because performance
was reduced to chance levels for all landmark loci in both
hemifields. In this instance, as the contralateral neglect
disappeared during bilateral cooling of pMS cortex, a new spatial
discrimination deficit was revealed across the entire visual
field. We conclude that pMS cortex contributes in multiple ways
to the analyses of space, and that these contributions cannot
be safely predicted from analyses of unilateral deactivations
or from one task to another. Moreover, it is clear that other
structures are capable of guiding orienting to high contrast,
moved targets when pMS cortex is eliminated from brain
circuitry. However, these same structures are incapable of
supporting either orienting to static stimuli or analyses
of spatial relations as tested with the landmark task.
The impact of reversible deactivation of the superior colliculus
on these same tasks is discussed.
Reversal of visual hemineglect: Differential influences of deactivating either contralateral posterior parietal cortex or the superior colliculus
