Abstracts

RATIONALE: Lovett et al. (1986) described poor organization of narrative with overuse of unclear/ambiguous pronouns for reference following left hemispherectomy, but well-organized narrative and appropriate reference use following right hemispherectomy. Evidence from normal adults (Caplan and Dapretto, 2001) and unilateral brain damage patients (Brownell et al., 1992) suggest that the left hemisphere is involved in understanding the reasoning and the right hemisphere in topic maintenance during conversation. This study examined how children who underwent hemispherectomy for intractable epilepsy used language to formulate their thoughts during conversation. We predicted that before and after surgery, children with a left or right hemispherectomy would differ in their discourse profiles with impaired reasoning and use of lexical ties (i.e., cohesion) following left hemispherectomy, but impaired topic maintenance after right hemispherectomy. We posited that these deficits would relate to postsurgical seizure control and type of underlying pathology.
METHODS: Reliable and valid reasoning, topic maintenance, and cohesion measures were coded from transcriptions of the Story Game (Caplan et al., 1989, 1992) of 19 children (8 boys, 11 girls), aged 10.7 (SD = 3.84) years, before and 15.3 (SD = 18.97) months after hemispherectomy (13 left, 6 right) . These scores were compared to those of 314 normal children, aged 5 - 18 years. Nine patients had cortical dysplasia and 10 had Rasmussen encephalitis. Thirteen patients had seizure control and at their last postoperative visit.
RESULTS: After correcting for age, a repeated measures analysis of variance demonstrated that, irrespective of the side of surgery, the patients had significantly more illogical thinking (p[lt]0.005), more loose associations (p[lt]0.08), and fewer utterances (p[lt]0.0001) before and after surgery compared to the normal children. They also made significantly fewer cohesive ties using conjunctions (p[lt]0.002), referential cohesion (p[lt]0.008), lexical cohesion (p[lt]0.004), unclear/ambiguous reference (p[lt]0.001), and substitution (p[lt]0.004) than the normal children. The children with an isolated right hemisphere, however, were significantly more impaired in using conjunctions (p[lt]0.02), referential cohesion (p[lt]0.03), and lexical cohesion (p[lt]0.03) than those with an isolated left hemisphere. There was a significant decrease in illogical thinking (p[lt]0.01) and substitution (p[lt]0.04) at the first postsurgical visit, but no subsequent improvement. Loose associations (p[lt]0.02), but none of the cohesion measures improved over time. The Rasmussen patients had significantly more topic maintenance and cohesion deficits than the cortical dysplasia patients. Postsurgical seizure control was unrelated to the findings.
CONCLUSIONS: These findings imply plasticity, albeit limited, in both left and right hemispheres for higher-level linguistic skills involving organization of thoughts and use of linguistic ties that connect ideas across sentences during conversation. Continued deficits after surgery suggest more limited plasticity in the isolated right hemisphere for cohesion. In children with cortical dysplasia, the isolated hemisphere might have more plasticity for higher-level linguistic skills than in Rasmussen encephalitis.
[Supported by: PO1 NS28383 and R01 NS39505]