Can transcranial direct current stimulation reduce hemispatial neglect? A study of ipsilateral activation and contralateral inhibition

A common deficit after stroke is hemispatial neglect. These patients ignore
stimuli on the contralesional side. Neglect is related to reduced functional
recovery and therefore it is important to develop effective treatment methods.
The proposed study will test a new method that is based on the idea that
neglect is a consequence of a imbalance between the attentional systems of the
two hemispheres. This model suggest that each cerebral hemisphere focuses
attention to the contralateral side of space. In neglect the attentional system
of the undamaged hemisphere dominates. To reduce this imbalance transcranial
direct current stimulation (tDCS) will be used. This method, that has been
proven to be safe, consists of a weak electrical current between two electrodes
on the skull that influences brain activity. One advantage of tDCS that so far
has not been investigated is that it allows simultaneously to activate the
attentional system in the damaged hemisphere and to inhibit the attentional
system in the healthy hemisphere. We anticipate that this bilateral stimulation
will result in a smaller imbalance between the two attentional systems and a
larger reduction of neglect symptoms than after single site stimulation.

The proposed study aims to test the acute effects of tDCS on chronic
hemispatial neglect. In this particular application of tDCS the damaged
hemisphere will be activated and the healthy hemisphere inhibited.

Each participating patient will commence with a baseline assessment. Two weeks
later treatment will be started. This will consist of two periods of treatment:
tDCS stimulation and placebo stimulation. In each period patients will be given
daily sessions of 20 minutes of stimulation on five consecutive days. The order
of the placebo and tDCS treatment periods will be counterbalanced across
patients. The two treatment periods will be separated by a period of four weeks
without treatment. The placebo condition will be indistinguishable from the
tDCS condition for the patient. tDCS and placebo treatment will be double
blind. During each stimulation period (placebo and tDCS) the patients will be
assessed before and after each stimulation session of 20 minutes on the
conventional subtests of the BIT. Assessment and treatment will be performed at
Utrecht University or at the patient's home (depending on the patients ability
to visit the university regularly).

Bilateral transcranial direct current stimulation (tDCS)

Each patient will be seen at four different times.
1. Baseline assessment
2. After twee weeks: tDCS or placebo stimulation (five consecutive days)
3. After another four weeks the other stimulation condition (five consecutive
days)
4. Follow-up assessment (four weeks after treatment cessation)

At the start of tDCS participants often feel a slight itch which disappears in
about one minute. The risks of tDCS are negligible. Investigations of the
possible effect of treatment on neglect can only be assessed in a group of
hemispatial neglect patients.