Nutritional conditions early in life constitute one environmental factor that can influence brain electrophysiological features. Cortical spreading depression (SD) is a brain electrophysiological phenomenon that can be altered by the early nutritional status of organism. SD-velocity changes were presently studied in young (30-40 days old) and adult (90-120 days) rats suckled in litters formed by 3, 6, or 12 pups (called respectively small (S), medium (M) and large (L) litters). Body weights and SD propagation velocities in the 3 groups varied, respectively in an inverse and direct way, in relation to the litter sizes. The present investigation provides the first systematic description of the effectiveness of favorable and unfavorable lactation conditions (respectively suckling in S and L litters) in altering cortical SD-propagation. The results confirm previous evidence in favor of permanent or at least long-lasting SD-changes associated to the prevailing nutritional status during the period of fast brain development.