Memory deficits before and after temporal lobectomy: effect of laterality and age of onset.

Laterality and age of onset effects on semantic and figural memory were evaluated in 30 right-handed, left speech dominant (amobarbital test) patients with epilepsy before and after temporal lobectomy. There were no effects of focus on WAIS-R IQ scores. Early onset (less than or equal to 5 years) was associated with lower IQ and memory (WMS). Left Temporal (LT) patients showed worse semantic than figural memory preoperatively. Unexpectedly, early onset LT had marked postoperative decline of figural memory, whereas late onset LT patients showed the previously reported worsening of semantic memory. Right Temporal (RT) lobectomy patients, in contrast, improved in both semantic and figural memory regardless of age of onset. A "crowding effect" was suggested by the decline in figural memory following surgery in the early onset LT patients who remained stable or improved in semantic memory. Results indicate the need to incorporate age of onset of seizures into laterality models of memory function following unilateral temporal-hippocampal resection.