Pattern discrimination learning in functionally hemidecorticate rats leads to formation of memory traces in the intact hemisphere. The interhemispheric transfer (IHT) of such lateralized engrams is more efficient when the untrained eye rather than the trained eye is used during interdepression training (10 trials) preceding the retention test with the contralateral hemisphere, probably because the untrained hemisphere is indispensable for readout in the first case (imperative IHT) but can be completely bypassed in the second case (facultative IHT). Monocular acquisition of a pattern discrimination habit induces a strong primary engram in the contralateral and a weak secondary engram in the ipsilateral hemicortex. The primary trace is further improved with overtraining while the secondary engram is abolished. During interocular transfer, the primary trace is at first read out through commissural fibers while a secondary trace is rapidly transferred to the untrained hemisphere. Pretraining administration of 2-pyrrolidone acetamide (Piracetam, 100 mg/kg) improves the secondary trace acquired during monocular pattern discrimination learning almost to the level of the primary trace, and facilitates the imperative IHT. Uncrossed optic projections and subcortical storage may contribute to IHT of brightness but not of pattern discrimination. It is concluded that IHT of visual engrams is mainly due to transcommissural encoding activated during learning or by transcommissural readout of lateralized traces.

Animals↗

PubMed1973

Cortical and subcortical components of conditioned saccharin aversion in rats.

Taste aversion was elicited in rats offered 0.1 percent saccharin (conditioned stimulus) for 10 min and then poisoned 30 min later by lithium-chloride (unconditioned stimulus - 0.14 M, 2 ml/100 g i.p.). Similar reduction of saccharin intake on the next day was obtained in rats learning the task with intact brain or under unilateral cortical spreading depression (CSD) and tested with CSD in the same or opposite hemicortex. No taste aversion developed in rats with bilateral CSD when forced swallowing of saccharin was followed after 5-30 min by LiCl injection. Bilateral CSD elicited 15 min after saccharin ingestion and maintained during the rest of the variable (30 min to 5 h) CS-US interval, decreased the saccharin aversion only with taste-illness delays exceeding 1 h. It is concluded that during the CS-US interval the taste information is stored both at the cortical and the subcortical levels. Normal cortical function is a necessary prerequisite for the formation of the nonlateralized subcortical engram which can be changed by association with the gastrointestinal distress into a permanent memory trace even under bilateral CSD.

Animals↗

PubMed1972