|Year : 1989 | Volume
| Issue : 3 | Page : 135-8
Study of reaction time in hemiplegics.
AA Malathi, VV Parulkar
A A Malathi
Visual reaction time and auditory reaction time (VRT and ART) were measured in 25 right hemiplegics and 25 left hemiplegics in the age group of 40-60 years. There was a significant prolongation of VRT and ART in both the right and left hemiplegics as compared to normals of the same age group. ART following mono-aural stimulation i.e. sound input into the right and left ear separately, was also studied in the subjects. Mono-aural stimulation revealed a prolongation of the ART on contralateral stimulation (i.e. auditory stimulation on the side, opposite to the brain damage) as compared to ipsilateral stimulation (auditory stimulation on the side of brain damage) in the right and left hemiplegics.
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Malathi A A, Parulkar V V. Study of reaction time in hemiplegics. J Postgrad Med 1989;35:135-8
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Malathi A A, Parulkar V V. Study of reaction time in hemiplegics. J Postgrad Med [serial online] 1989 [cited 2022 May 24 ];35:135-8
Available from: https://www.jpgmonline.com/text.asp?1989/35/3/135/5699
The study of reaction time (RT) has provided an indirect index of capabilities of CNS processing and forms a basis of investigating sensory-motor performance with respect to brain damage. RT can discriminate between grades of severity of brain damage and the recovery is reflected in the overall decrease in the RT. RT is independent of social-cultural influences and can purely indicate the efficiency or dysfunction of biological process in brain. For any response to occur the stimulus initially activates the sense organs and the impulse is then conducted to the brain and from the brain is sent back to execute the movement required to accomplish the task. Slowed performance is usually accompanied by prolonged simple RT and is a function of the severity of brain damage., Results from recent studies suggest that RT can provide an index of cerebral damage localized within one hemisphere. Thus this study was undertaken to determine the effect of brain damage on VRT and ART. Also, the mono-aural RT was determined to find out the effect of ipsilateral and contralateral stimulation by auditory stimulus on reaction time.
MATERIAL AND METHODS
VRT and ART (binaural) were measured in 25 right hemiplegics and 25 left hemiplegics of 40-60 years of age and compared with that of 25 controls of the same age group. RT measurements were made with the apparatus described by Malathi and Parulkar. ART was determined by (a) stimulation of both ears simultaneously (ARTa), followed by (b) stimulation of right ear and (c) left ear individually (ARTb and ARTC respectively) with the help of headphones. The hemiplegic subjects used the unaffected hand (i.e. right hand by left hemiplegics and left hand by right hemiplegics) to press the `stop' button. The control subjects too used the same hand to press the stop button as the corresponding group with whom they were compared (i.e. right hand when comparing with left hemiplegics and left hand when comparing with right hemiplegics).
Readings compared were as follows.
(a) VRT and ART of controls using right hand and left hand.
(b) VRT of controls with VRT of right and left hemiplegics.
(c) Binaural RT (ARTa) of controls with the binaural RT of right and left hemiplegics.
(d) Mono-aural RT (right ear and left ear separately) of right hemiplegics and left hemiplegics (ARTb and (ARTc).
VRT and ARTa measurements in the control subjects did not show any statistically significant difference using right hand or left hand [Table 1] There was a statistically significant prolongation of both VRT and ARTa of right and left hemiplegics as compared with the controls[Table 2]. Mono-aural stimulation i.e. sound input in the right ear (RE) in the right hemiplegics produced a prolonged RT as compared to the auditory input into the left ear (LE) [Table 3].
Similarly auditory stimulus in the LE in the left hemiplegics produced a longer RT as compared to sound input in the RE. [Table 3].
VRT and Binaural ART (a): As seen in our studies there was a prolongation of VRT and ARTa in the right and left hemiplegics as compared to normal controls of the same age group. This may be related to the lower signal strength due to underarousal in the brain-damaged groups. This observation compares with that made by Dee and Van Allen. The brain damaged subjects included in the latter study were slower over all, so that injury to any part of the brain can produce prolongation of RT. Work done by Van Zomeren and Deelman on long term recovery of VRT after closed head injury showed that there was a slowing of information processing, thus indicating that brain damage influences the channel capacity rate of information processing in the CNS. The underarousal states have been reported by Growall and Sampson (as quoted by Malathi and Parulkar) who have suggested that brain damaged patients may be in a state of 'chronic underarousal' due to dysfunction of the brain stem. D'costa found that RT of brain damaged subjects were prolonged as compared to the controls. Similar increase in RT was also demonstrated by McDonald and Burns who felt that the increase was not due to motor incapacity and it might serve as a possible indicator of insult to the basal ganglia.
In 1978, studies on long term recovery of VRT in brain damage using preferred hand revealed no change in RT. In our study the patients were allowed to respond with the preferred hand i.e. normal hand. Though right hemiplegics used the left hand and left hemiplegics used the right hand this could not account for the change in RT as RT measurements in normal subjects with either hand did not show any significant difference. Also the controls used the same hand as the hemiplegic subjects. Misra et al have also demonstrated a similar finding in males using right or left hand.
Mono-aural stimulation: Mono-aural stimulus excites contralateral cortical neurons of the auditory cortex. The right and left sound fields are represented in the contralateral hemispheres. Measurements of gross cortical evoked potentials in response to contralateral and ipsilateral stimulation have demonstrated larger evoked potentials elicited by stimulation of contralateral ear., In our study an auditory stimulus input into the right ear (contralateral stimulation) in the right hemiplegies produced a prolongation of RT as compared to auditory input into the left ear. This is probably because of the predominant contralateral representation of the auditory cortex in the left hemisphere for auditory input into the right ear. However, as the left cerebral hemisphere is damaged in the right hemiplegies it would account for the increase in RT. Ipsilateral stimulation of the left ear (same side as damage) showed a shorter RT as compared to right ear input as the predominant auditory representation of the left ear would bin the right cerebral hemisphere which is normal. Similar results in the left hemiplegics could be due to the same reasons as in the right hemiplegies. Benton and Joynt have also found a prolonged RT in persons with localized brain lesions, although RT contralateral to the damaged hemisphere was affected more than those with ipsilateral stimulation.
Thus comparing contralateral and ipsilateral RT can help to establish whether brain damage is predominantly in, or restricted to one cerebral hemisphere. Although diffuse forms of damage can result in changes in RT, it can play a role for measures of psychomotor performance and provide valuable information backed by clinical judgement.
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