Recovery from cortical blindness mediated by destruction of nontectotectal fibers in the commissure of the superior colliculus in the cat

Abstract

Transection of the commissure of the superior colliculus restores visual orientation behavior to a cat previously rendered hemianopic by a unilateral visual cortical lesion (the Sprague effect). Using two methods, we asked whether this recovery resulted from the severing of the tectotectal component of the commissure or whether the destruction of some other connection was responsible. First, we transected either the rostral or the caudal one-half of the tectal commissure in hemianopic cats. If destruction of tectotectal fibers is responsible for the Sprague effect, then only rostral transections should produce the recovery since nearly all tectotectal connections lie in the rostral one-half of the commissure. However, rostral cuts failed to produce a recovery, whereas caudal commisurotomies did. Second, ibotenic acid was used to destroy the cells in the superior colliculus contralateral to the cortical lesion. This lesion eliminated the contralateral tectotectal pathway from the contralateral colliculus but left other fibers (originating elsewhere but coursing through the commissure) largely intact. These ibotenic acid lesions failed to produce the recovery; but when the caudal portion of the tectal commissure was subsequently transected in the same animals, the recovery was observed. The results of both experiments support the conclusion that the transection of a nontectotectal component of the commissure of the superior colliculus is responsible for the recovery of visual orientation behavior in a cortically blind cat.

On imputing function to structure from the behavioural effects of brain lesions

“…We note that these uncertainties about double dissociation would not have been emphasized without the startling and paradoxical e¡ects of multiple inactivations, made apparent by careful studies of this system (e.g. Sprague 1966;Lomber & Payne 1996;Wallace et al 1989Wallace et al , 1990.…”

Attention to One or Two Features in Left or Right Visual Field: A Positron Emission Tomography Study

“…These lesion data and the current findings require us to postulate a model in which covert orienting results from the balance among inhibitory, disinhibitory, and facilitatory influences within a distributed attentional system, including the lateral frontal cortex. The complex interplay among different components of such a system may be reminiscent of much better known oculomotor (Wallace et al, 1989(Wallace et al, , 1990) and motor systems (Alexander et al, 1986). Within such a model the absolute sign of the frontal blood flow difference is hard to interpret and may reflect inhibitory, disinhibitory, and facilitatory influences.…”

Topographic Organization of Excitatory and Inhibitory Commissural Connections in the Superior Colliculi and Their Functional Roles in Saccade Generation

“…Many anatomical and behavioral studies on the collicular commissural connections have been devoted to showing the neural mechanism of the Sprague effect (Stein and Meredith 1993). However, more recent studies have shown that this effect is mediated by a pathway other than intrinsic collicular commissural neurons (CNs), because transection of the rostral commissure in the SC, where fibers of the intrinsic collicular CNs are known to run, produced no effect, whereas transection of the caudal commissure produced the Sprague effect (Wallace et al 1989(Wallace et al , 1990.…”