Rowland 2023 - Hemianopia and Multisensory Training

 Amerliorating Hemianopia with Multisensory Training (Rowland et al., 2023)

This paper presented evidence that visual-auditory stimulation therapy is a rapid and effective method for restoring visual function in patients with hemianopia.

Hemianopia/ Hemianopsia/ Anopsia is a loss of vision that affects one side of the field vision resulting in unilateral blindness or loss of sight on either left or right half part of both eyes. It is a common consequence of s stroke and trauma to visual cortex.

Key Takeaways

• This study discusses a multisensory therapy that may be effective in restoring visual sensitivity in hemianopia.
• The therapy was tested on two male human patients who had been suffering from the disorder for at least 8 months following a stroke. So the cause was brain trauma rather than a lesion looked at in earlier animal studies. 
• After several weeks of exposure to congruent visual-auditory stimuli (10 sessions over 8 months), both patients recovered their ability to detect and describe visuals throughout their formerly blind field within few weeks. 
• They could also localize these stimuli, identify some features and perceive multiple visuals simultaneously in both fields indicating that this multisensory approach is an efficient method for treating hemianopia quickly with positive results.

Participants: 

64 year old JM joined the study 14 months after a stroke (infract in left & right PCA)
74 year old CW joined the study ~18 months after an myocardial infarction and cardiac arrest (right infract along with scattered infract in cerebellum bilateral supratentorial cerebral hemispheres )

This meant that CW had a larger sighted visual field compared to JM who had a second PCA infract. 

But both patients had loss of vision in the left visual field. 
Prior to joining the study both had been referred to PT and OT as rehabilitation measures. 

Method
The patient sat in front of height-adjustable tall towers, which were used to present auditory-visual stimuli at different locations of the blind field. They had to look at a central fixed point and point/speak to indicate if they saw a stimulus.

 

Results: 

1. Vision Detection

Dramatic results. Both patients recovered the ability to detect and describe visual stimuli throughout their formerly blind field within a few weeks. They could also localize these stimuli, identify some features, and perceive multiple visuals simultaneously in both fields. CW who had a larger sighted visual field, prior to study had more rapid progress, compared to JM who had a second PCA infract.

The study concludes that multisensory therapy is an effective method for restoring visual function in hemianopia quickly with positive outcomes.


Figure 1 shows the patients' ability to detect the flashed stimulus at the beginning of select sessions over the course of the experiment. Unshaded regions indicate areas where responses were elicited by the flash stimulus and black shaded regions indicate where they were not elicited. The icon (a flash in a circle) indicates the location of the visual-auditory training stimulus in the previous session. Dashed and solid circles (connected by arrows) in the last of JM’s figures (see session 6) represent his translocation of visual stimuli in the far periphery of the rehabilitated field, which were systematically biased to a compressed, more central range.


2. Visuospatial extinction

Additional observations in the study were around Visuospatial extinction, which is when a person is unable to detect a stimulus in one hemifield when a stimulus is simultaneously presented in the other hemifield.


Figure 2 shows the regions where a bright light could or could not be detected in the left hemifield when an equally-bright light was simultaneously presented in the right hemifield. The black shading indicates the regions where the light could not be detected before the therapy, while the gray shading indicates the regions where the light could be detected after the therapy. The unshaded areas indicate the regions where both lights could be perceived 

Discussion

The mechanism by which visual-auditory stimulation therapy restores visual sensitivity in hemianopia is not fully understood. However, it appears to exploit the multisensory architecture of the brain and involves cooperative dynamics between adjacent neurons in a topographic map along with other circuits such as midbrain, thalamus and cortex that may contribute to this process. The recovery begins from the margin of sighted field rather than at training location suggesting Hebbian mechanisms are involved.

The paper suggests that the multisensory architecture of the brain enables this type of therapy to be effective by allowing for cooperative dynamics between adjacent neurons in a topographic map. This allows visual and auditory stimuli to interact with each other, which can lead to plasticity changes that result in improved vision within the formerly blind field. Additionally, midbrain, thalamus and cortex circuits may also contribute towards recovery from hemianopia through their involvement in these processes

It is not known whether this type of rehabilitation works better for certain types of strokes than others. However, it appears that the multisensory therapy may be more effective in restoring visual function when there are residual regions within the damaged areas of visual cortex which can still interact with auditory stimuli and facilitate plasticity changes. Additionally, since this technique does not require active engagement or alertness from patients to achieve results, it could potentially work well even under anesthesia or other conditions where cognitive factors might otherwise limit success rates

The authors suggest that the result is replicable in larger sample size or a different patient population. A more comprehensive study involving a greater number of patients and/or those from diverse backgrounds would be necessary in order to determine the generalizability of this multisensory therapy for restoring visual function in hemianopia. Additionally, further research could also explore whether early interventions might yield faster or more robust recovery outcomes compared to later ones as well as if plasticity engaged through such therapies may degrade over time.

Terms Explained

• Infract: Area of tissue death caused by lack of blood supply