Jump-starter for the brain

4/14/2017

Jump-starter for the brain: Direct-current stimulation for the treatment of blindness after stroke

Alber R., Moser H., Gall C., Sabel B.

Stroke is the leading cause of serious disability in adulthood. Every year about 25,000 Austrians are affected. Although the majority of patients are no longer of working age, yet 5.6 % of the persons affected are between 18 and 45 years, and 8.5 % between 46 and 55 years of age.¹ In addition to motor, sensory or cognitive impairments, in about 23 % of patients also visual field defects – called anopsias or anopias – are found. These visual impairments vary in severity, but in the worst case they massively impair the patients’ ability to drive and work. In addition to these existential limitations, patients often also suffer significant detriments to their quality of life, as reading, spatial orientation, search and retrieval of objects and many other activities of daily living are affected, and the risk of accidents is significantly increased. Thus, optimal restoration of these functions is not only of high social but also of personal interest for those affected and their families.

During the last 30 years, some therapies and training methods have been specifically developed for these types of disorders. However, as the regenerative capacity of the visual pathways and the visual center in the brain was previously believed to be very limited, most procedures were designed with compensation, i.e. balancing of the deficiencies, in mind. Compensation is achieved e.g. through frequent and targeted eye movements (saccades), targeted search strategies (exploration), or more rarely by use of prism sheets on eyeglasses, which project the image impression of the blind visual field into the healthy field. In the late 1990s, Prof. Erich Kasten and Prof. Bernhard Sabel at the Institute of Medical Psychology of the Otto von Guericke University Magdeburg developed a method for the restoration of lost vision. Using Vision Restoration Therapy (VRT), by means of special software on an ordinary screen exactly at the border between the blind and functional visual field targeted light stimuli are presented, which the patients must confirm by pressing a key.² By high-frequency training, the brain “practices” responding to light stimuli again, thus gradually expanding the limit of vision. In order to achieve significant effects, patients had to work for up to 300 hours, but they could do this at home.

How can we reduce this therapeutic effort and achieve even stronger effects? This was the question asked by neuropsychologist Raimund Alber and chief physician Dr. Hermann Moser, neurologist and medical director of the neurological therapy center Gmundnerberg.

With the help of Professor Bernhard Sabel and his work group at the Institute of Medical Psychology at the University Hospital in Magdeburg, they developed a concept for a treatment protocol combining Vision Restoration Therapy with an increasingly popular technique, transcranial direct current stimulation (tDCS).

This computer simulation shows the expected current upon transcranial direct-current stimulation of the occipital and the visual center in the brain.

Countless studies have shown that by means of weak direct currents (up to 2 mA) applied non-invasively on the skull, the spontaneous activity of the neurons located beneath the electrodes can be influenced. Depending on the direction of the current flow, neurons are stimulated or inhibited. However, the excitation of nerve cells itself leads only to limited neuroplastic processes (modification and optimization of the anatomy and function of synapses, nerve cells or entire areas of the brain).³ An underlying function, which is processed in the neurons or in a neuronal network, is always important. This hypothesis is further corroborated by studies of direct-current stimulation in cases of paralysis after stroke, where combination of tDCS and physiotherapy was investigated.

Another novelty of this experiment is the use of this treatment relatively briefly after the stroke. So patients were treated in the subacute phase, i.e. from four weeks to 6 months after the event – in keeping with the notion that time is brain. The idea was to exploit and further increase the full potential of spontaneous remission. In a pilot study ³ in 7 patients, the encouraging result was found that there were no adverse effects of the electric stimulation after 10 treatments. Comparison of the stimulated patients with a group of patients who received a standard training showed a clear advantage for the stimulation group. Average light sensitivity, i.e. the sensitivity of the light perception of the central visual field (60 °) as measured by perimetry, was compared. In the control group, perceptive performance improved by an average of 10.81 %; in the stimulation group, by 36.93 %.

The visual fields of this patient represent areas of complete blindness (absolute defects: red), impaired perception of light (relative defects: yellow) and normal vision (green). Comparison of the red zones before (PRE) and after (POST) treatment shows clear reduction of the blind area. The improvement proceeds gradually. Absolute defects (AD) become relative defects (RD), and relative defects improve to a normal level. These results demonstrate considerable dynamism of the damaged brain tissue, where previously it was believed that no changes were to be expected from absolutely blind areas anymore.

Although this experiment suggests a distinct direction, the present results should not be overrated. In a subsequent study, current stimulation will have to compete with sham stimulation, with neither the patient nor the physician being informed whether electricity is applied to the electrodes or not. Only in this manner can placebo and experimenter effects be excluded. However, not only perceptive performance but neurophysiological processes as well were analyzed. Using electroencephalography (EEG), by now extensive network processes can be investigated. In a study by Michal Bola from the Magdeburg work group it was shown that large networks up to the frontal lobe are required for visual processing, and are impaired in neurological diseases. These impairments could be positively influenced by targeted stimulation with alternating currents⁴. Whether direct-current stimulation achieves similar effects, is still being evaluated.

In this pilot study it could be shown that tDCS is safe and without side effects even briefly after the stroke. In addition, effects could be measured that suggest that regeneration of the brain after a stroke can be significantly increased using functional training and “electrical jump-starting”.

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