Developmental Neuropsychology: Mild spastic cerebral palsy

Mild spastic cerebral palsy: An event-related brain potential study of error detection and response adjustment 

The term cerebral palsy is used to define a number of disorders which affect posture and movement. Cerebral palsy is attributed to damage or abnormal development in the developing brain of fetus’s or infants. Though there are many contributing factors to cerebral palsy, one of particular note are infarcts (tissue death as a result of lack of oxygen) which lead to lesions in white and grey matter tracts. These lesions to white matter tracts are detrimental to executive functioning which has been proven when testing youths with cerebral palsy against a control group without.

The question posed by this study is whether youths with mild spastic cerebral palsy are aware of their errors when carrying out tasks requiring executive functioning.

It has often been the findings of neurocognitive research that poor motor preparation precedes error making. Error detection and the adjustments which follow are measured in this case using response-locked error-related negativity. The brain potential for incorrect responses is markedly higher than those following correct responses.

Method

Participants consisted of 11 patients, with a mean age of 14 years, diagnosed with mild cerebral palsy and a control group of 12 youths without cerebral palsy, with a mean age of 14, recruited from the same city. Though the intelligent quotient of some of the youths with mild cerebral palsy was within the range of learning disabilities, none were classified as being mentally retarded, as their daily lives were intact.

A computer based stimulus recognition task and electroencephalograms were used to record brain activity in the study. The task used was comparable to the Sternberg short-term memory paradigm. Participants were presented with 2 letters to be memorized, then were subsequently shown 4 letters, one or none of which were the letters which were memorized. Using two response buttons, participants would indicate either yes or no whether they identified there target letters in the new set. Reaction time was measured starting when the new set appeared until a button was pressed. Total time for the experiment was about 15 minutes.

Results

The results of the experiment find that the control group made more correct responses and less error responses than the experiment group. In addition, the patient group reacted slower on average than the control group. Error responses were also shown to be slower than correct responses, which proved true for both groups.  

Discussion and conclusion

Given the findings of the study, poor motor preparation appears to be associated with error responses. This is especially salient in the patient group. Error detection was found in both groups and went on to predict better performance. A key point given by the authors is that error monitoring and the adjustment in performance which follows are essential to learning. The research conducted here implies that this process is thankfully present  in the patient group. Additionally, it is proposed that the patient group was more sensitive to their error making than the control group. This suggests that motivation may also be a key to learning in the patient group.

This leads to the suggestion that the patient group possesses an intact top-down capacity for executive functioning in tandem with a diminished motor action system. This calls for further investigation into the period preceding the execution of an action (i.e. pushing the button) to pinpoint the origin of error making in youths with mild cerebral palsy.

Limitations

It must be noted that the study contained a rather small sample size and should be treated as preliminary research.

Mild spastic cerebral palsy: brain state before error making 

While the previous article focused on whether youths with mild cerebral palsy were aware of their own error making and what adjustments they made to avoid future error, the following article asks whether error making is preceded by attentional lapses, by poor motor preparation, or both.

As mentioned in the previous article, the term cerebral palsy is used to define a number of disorders which affect posture and movement. When addressing the subject of quality of life, how well one has a capacity for executive functioning is a relevant question. The term executive functions encompasses a wide range of cognitive faculties including attention control, inhibitory control, and cognitive control. Taken as a whole, executive functioning governs ones capacity to function effectively in life. Recent research indicates that reduced capabilities towards executive functioning has been found in youths with cerebral palsy. This hypothesis is limited, however, for two reasons. Firstly, poor effectiveness by patients with cerebral palsy on executive functioning tasks may be due to their diminished motor system as opposed to deficiencies in cognition. Secondly, weak cognitive skills on cognitive tasks are measured by high error count and slow reaction speed.

Given the previous research conducted by the authors on event-related potential, they  propose that it is the poor motor preparation preceding a stimulus which is casually associated with error making in individuals with cerebral palsy. In accordance to this, the aim of this study was to measure what happens in the brain preceding errors in both the control and patient groups. To accomplish this, 3 event-related potential elements were recorded:

• Motor preparation (frontal late contingent negative variation)
• Attention (parietal P300)
• Response evaluation (parietal error-preceding positivity)

Methods

Participants consisted of 11 patients with cerebral palsy and an average age of 15, and 12 youths with an average age of 14 as a control group. The study design did not differ from that of the previous study. Again, the computer task was administered and responses were recorded as the interval between the new display set and the button press. However the authors were only interested in the 3 successive correct responses preceding an error.

Results

Overall, the patient group had fewer sequences of 3 correct trial than the control group (patient group 41 sequences; control group 47). Both accuracy of responses and reaction speed were not found to be of a significant difference between the groups. It was found that contingent negative variation (motor preparation) was weakened for the patient group preceding an error. Attention (P300) levels preceding error making were shown to be low, however this was true for both groups. In the case of response evaluation (error preceding positivity), the groups did not show a difference in their level of performance monitoring preceding an error.

Discussion and conclusion

The results of the study show a strong indication that youths with mild cerebral palsy experience  poor motor preparation not only preceding an error, but already one trial before the error occurs.  Given that the control group and patient group did not differ on the amplitude of the parietal P300, the authors conclude that the cognitions responsible for response monitoring were similar in both groups. During the trials the patient group showed high levels of cognition control both preceding and following error making. Despite this however, they still made more errors than the control group. The authors propose that the poor motor preparation could be an indicator of a conflict between motor and cognitive exertion.

Ultimately, the goal of the study was to find out if error making in the patient group was associated with weak cognitive abilities. Given that the results indicate the source of error as a weakened motor system, they hypothesize that weak cognitive abilities can be dismissed as the source of error.

Limitations

As with the previous study, the sample size was small. As such it should be taken as a preliminary study. Additionally, the generalizability is questionable, as it only deals with patients with mild cerebral palsy. Other measures of executive functioning would also be an improvement.