Patterns of recovery following focal hemispheric lesions: relationship between lasting deficit and damage to specialized networks.

PURPOSE

Cognitive deficits that are present in the acute stage of a focal hemispheric lesion tend to be greater and more general than residual deficits, which persist into the chronic stage. We have investigated the patterns of recovery and the relationship between deficits and damage to specialized networks taking as model auditory cognitive functions. Evidence from human psychophysical, activation and neuropsychological studies suggests that sound recognition and sound localization are processed in anatomically and functionally distinct cortical networks, the auditory "What" and "Where" processing streams, that are each present in both hemispheres. Focal left or right hemispheric lesions centred on these networks were found to be associated, in the chronic stage, with the corresponding deficits in sound recognition and/or sound localization.

METHODS

We report here on recovery patterns in 24 patients who sustained focal hemispheric lesions and were deficient in sound recognition, sound localization and/or sound motion perception at a first evaluation in the acute (n=9), subacute (n=6) or early chronic stages (n=9).

RESULTS

All 24 patients had initially a deficit in sound localization and/or sound motion perception. In the acute stage this deficit occurred without damage to the auditory "Where" stream in almost half of the patients, a situation which was never observed in the early chronic stage. Lack of recovery tended to be associated with damage to the specialized stream plus the persistence of deficits beyond the acute stage, and was only loosely related to the size of the lesion and to the extent of damage to a specialized network.

CONCLUSIONS

Our results suggest that different mechanisms underlie deficits and recovery at different time points.