Training-induced cortical representation of a hemianopic hemifield

Background

Patients with homonymous hemianopia often have some residual sensitivity for visual stimuli in their blind hemifield. Previous imaging studies suggest an important role for extrastriate cortical areas in such residual vision, but results of training to improve vision in patients with hemianopia are conflicting.

Objective

To show that intensive training with flicker stimulation in the chronic stage of stroke can reorganise visual cortices of an adult patient.

Methods

A 61‐year‐old patient with homonymous hemianopia was trained with flicker stimulation, starting 22 months after stroke. Changes in functioning during training were documented with magnetoencephalography, and the cortical organisation after training was examined with functional magnetic resonance imaging (fMRI).

Results

Both imaging methods showed that, after training, visual information from both hemifields was processed mainly in the intact hemisphere. The fMRI mapping results showed the representations of both the blind and the normal hemifield in the same set of cortical areas in the intact hemisphere, more specifically in the visual motion‐sensitive area V5, in a region around the superior temporal sulcus and in retinotopic visual areas V1 (primary visual cortex), V2, V3 and V3a.

Conclusions

Intensive training of a blind hemifield can induce cortical reorganisation in an adult patient, and this case shows an ipsilateral representation of the trained visual hemifield in several cortical areas, including the primary visual cortex.Homonymous hemianopia refers to blindness of a visual hemifield, a common symptom after a lesion in the occipital cortex or in the retinocortical pathway behind the optical chiasm. Neuroimaging studies have indicated residual responsiveness to blind hemifield stimulation in the extrastriate^1,2,3,4,5,6 and spared calcarine cortex,⁷ but studies on improvements of residual vision using training have reported conflicting results. Training of visual functions is not a standard procedure after a local cerebral damage, whereas benefits of motor rehabilitation and reorganisation of the motor cortex are widely accepted.⁸ Plasticity in the primary visual cortex (V1) has been described in primate studies,⁹ but there is an ongoing debate on the capacity of adult V1 for major long‐term reorganisation.^10,11 Overall, there is no previous report on a patient whose hemianopia had been intensively trained and the cortical effects of this training studied with functional imaging.This report describes cortical reorganisation of an adult male patient with homonymous hemianopia. His visual functions in the blind hemifield were trained using difficult detection tasks of flickering discs and recognition of flickering letters. The training procedure and follow‐up findings of psychophysical and neuromagnetic results for this and another patient are described in detail by Raninen et al.¹² Spontaneous recovery during training in this patient was unlikely, because training began in the chronic stage of the stroke. We were careful not to let eye movements or stable eccentric fixation contaminate the results.