For stroke patients whose visual awareness is impaired on one side, merely offering a reward improves their attention. That is the result of a recent study that tested how stroke patients respond to stimuli when offered a financial incentive.
As reported in the Journal of Neurology, Neurosurgery, and Psychiatry, the researchers gave a simple test to stroke patients suffering from a condition called “spatial neglect,” which leads to reduced visual awareness of one side of space. The patients would receive £1 for each coin they circled on a sheet of paper with many other similar-looking round objects, or would receive no reward for a similar exercise with buttons. At a later date, the patients retook the test and, again, were promised money for correct answers on the coin, but not the button, test. On the second visit, most patients performed better on the coin test but there was no such improvement for the button test.
CNS talked with Paresh Malhotra of Imperial College Londonabout the study, to learn more about spatial neglect, the study design, and future results he and colleagues will be presenting at the CNS 20th anniversary meeting in San Francisco this April.
CNS: What is spatial neglect? What are some examples of how it manifests itself in stroke patients?
Malhotra: Spatial neglect is a disorder of attention that is most frequently caused by stroke. Patients with neglect tend to be unaware of items, events, and people on the side opposite their brain damage. It is most common following right hemisphere stroke, so the majority of the patients we see have left-sided neglect. This can lead to patients having difficulty with noticing people on their left side or eating food on the left side of their plate, as well as potentially bumping into things when trying to get around. A particularly striking sign of neglect is when a patient who is asked to draw something only draws on one side – for example, only putting the numbers from one to six in a clock face, and completely omitting seven to twelve. A recent video that we made with two patients and their families is available online.
CNS: How did you and colleagues devise the idea to test the effects of bestowing a reward on spatial neglect?
Malhotra:We had seen that there was an increasing body of work showing that reward could modulate attention in healthy individuals, and we thought it would be interesting to assess whether reward could reduce pathological deficits in attention. We decided on the idea of adapting a standard pen-and-paper cancellation task [using coins/buttons as targets] so we that we could examine whether reward could actually affect spatial neglect on a standard test frequently used in the clinical setting.
CNS: What do you think is the link between reward and attention?
Malhotra: I think reward seems to have a number of effects, but it clearly biases attention. In addition to potentially boosting overall arousal, there is plenty of work, from the labs of Leonardo Chelazzi, Steve Yantis, and Martin Eimer, among others, that association of reward with particular stimuli biases attention towards those stimuli and increases their salience, regardless of whether the bias is to the benefit or detriment of task performance. In addition, functional imaging work has shown that rewarding feedback appears to have both a general influence on higher visual areas, as well as a more specific response in the primary visual cortex.
CNS: How does this work fit into past work in the field?
Malhotra: There is an interesting literature suggesting that motivational stimulation can influence spatial neglect. Almost 30 years ago, Marsel Mesulam described how an individual patient responded to being offered a penny for every target found on a search task. Since then, other authors have shown that introducing a potentially motivational task component, such as numbering of targets, can improve spatial neglect on a search task. More recently, David Soto, one of the authors on the current paper, and colleagues showed that the visual awareness of patients with spatial neglect improved if they were listening to music that they liked, but showed no such improvement when listening to music that they didn’t like. I think our paper follows on very well from these previous studies.
CNS: How could this work translate into behavioral therapies?
Malhotra: Obviously we can’t give all our patients money, but I do think the work has practical implications for rehabilitation. Systematic incorporation of motivational strategies and social rewards into therapy is likely to be beneficial. Follow-up studies will allow us to see whether the benefits of reward cross over to other tasks and more everyday situations, and also whether reward and motivation can modulate other disorders caused by brain damage and neurodegenerative diseases.
CNS: Were there any surprising reactions of the patients in the experiment?
Malhotra: Two patients showed no response to reward in the experiment, and interestingly, both these patients had damage that included the striatum. The striatum is known to be a key structure in reward processing, and when we explored some of the previous animal work, we found that if experimental lesions involved striatum, they tended to cause spatial neglect or make it particularly severe. I think that it will be very interesting to pursue this further, and it might provide some clues as to why animal models of neglect have not neatly mirrored the human syndrome.
CNS: What are the next steps for the research? And you mentioned you will be presenting on this work at the upcoming CNS meeting in San Francisco (April 13-16) – can we have a sneak peak at what you’ll be presenting?
Malhotra: We know from past research that dopamine is the key neurotransmitter associated with reward processing, and there is evidence suggesting that dopamine-related treatments can improve spatial neglect. Therefore, we are starting to examine how the reward effect relates to dopamine responsiveness in these patients and whether reward response is a predictor of response to drug treatment.
In addition, we have started to look at how reward affects discrete components of attention, and at the next CNS meeting, we will be presenting data showing reward’s effects on the pathological “attentional blink” that has been described in stroke patients, particularly those with neglect.
“Reward modulates spatial neglect,” Paresh A. Malhotra, David Soto, Korina Li, Charlotte Russell, Journal of Neurology, Neurosurgery, and Psychiatry, October 29, 2012.
Media contact: Lisa M.P. Munoz, CNS Public Information Officer, firstname.lastname@example.org