On How Psychophysical Thresholds are Altered by Unilateral Brain Injury Due to Stroke

OBJECTIVE: This study examined whether and how the absolute thresholds and the just noticeable difference thresholds for eleven, sensory/perceptual continua are altered by unilateral left and right hemisphere lesions due to stroke relative to healthy subjects. METHODS: The three subject groups were those with unilateral right hemisphere lesions (n=21), with unilateral left hemisphere lesions (n=13), and age-matched control subjects (n=76). Absolute thresholds of sensory detection and just noticeable difference thresholds were assessed for perceptual continua spanning the visual, tactile, proprioceptive, thermal, and gustatory sensory modalities. For stroke subjects, brain lesions were analyzed using subtraction techniques and volume analysis with the MRIcro and MRIcroN software programs. Stroke subjects also complete tests for spatial neglect, stroke severity and functional independence. RESULTS: There was no significant difference among subject groups regarding gender, race, hand dominance, age, or educational composition. There was no significant difference between subjects with right and left hemisphere lesions on measures of function, stroke severity, or lesion volume except for those with spatial neglect. The RHL group had a higher percentage of impaired perceptual continua (16%) than both normal controls (4%) and the LHL group (9%). If a stoke subject had an impaired threshold on one side of the body, they were ~5 times more likely to have an impaired threshold on the other side of the body. This result was more consistent and even exaggerated (~8 times more likely) in the small percentage of normal control subjects who demonstrated “impaired” sensory thresholds. Lesion volume was positively correlated with stroke severity and sensory threshold impairment, and it was negatively correlated with functional independence. CONCLUSIONS: When subjects, have difficulty detecting and discriminating sensory experiences, they tend to do so on both sides of the body. Unilateral right hemisphere stroke appeared to increase the relative frequency of altered thresholds occurring on the contralesional side of the body even though they made errors on both sides.