Table 6.

Total and regional brain volumes in 2011 in identical twin pairs discordant for LEP in 1999 (adjusted for birthweight)

Structure	Mean weaker twin (LEP in 1999)	Mean stronger twin (LEP in 1999)	Difference	Paired t test, one-tailed p
Ventricles/ICV	0.523	−0.016	0.540	0.025
Total grey matter/ICV	−0.523	0.053	−0.577	0.025
Left MTL	0.257	−0.003	0.261	0.890
Right MTL	0.153	−0.175	0.329	0.843
Left middle frontal gyrus	0.149	0.185	−0.036	0.444
Right middle frontal gyrus	0.335	0.312	0.023	0.550

ICV = Intracranial volume. Volumes are expressed as standardized scores for the whole sample. A negative difference score indicates the weaker twins have on average smaller volumes; conversely, positive difference scores mean the weaker twins have larger volumes.