The magnocellular mediodorsal thalamus is necessary for memory acquisition, but not retrieval - PubMed (original) (raw)

The magnocellular mediodorsal thalamus is necessary for memory acquisition, but not retrieval

Anna S Mitchell et al. J Neurosci. 2008.

Abstract

Damage to the magnocellular mediodorsal thalamic nucleus (MDmc) in the human brain is associated with both retrograde and anterograde amnesia. In the present study we made selective neurotoxic MDmc lesions in rhesus monkeys and compared the effects of these lesions on memory acquisition and retrieval. Monkeys learned 300 unique scene discriminations preoperatively and retention was assessed in a one-trial preoperative retrieval test. Bilateral neurotoxic lesions of the MDmc, produced by 10 x 1 microl injections of a mixture of ibotenate and NMDA did not affect performance in the postoperative one-trial retrieval test. In contrast, new postoperative learning of a further 100 novel scene discriminations was substantially impaired. Thus, MDmc is required for new learning of scene discriminations but not for their retention and retrieval. This finding is the first evidence that MDmc plays a specific role in memory acquisition.

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Figures

Figure 1.

Figure 1.

Schematic diagrams of six sections, 1 mm apart, through the medial thalamus of a monkey taken from Gaffan and Murray (1990) and photomicrographs of a normal medial thalamus (NORM) corresponding as closely as possible to the schematic diagrams. For abbreviations, see Mitchell et al., (2007a).

Figure 2.

Figure 2.

MDmc lesions. Photomicrographs of the MDmc lesions for MD4, MD5, and MD6 corresponding as closely as possible to normal medial thalamus (NORM) and the schematic diagrams of Figure 1 are shown. Arrows indicate the borders of each lesion.

Figure 3.

Figure 3.

Preoperative and postoperative retention (left). The mean number of total errors made during the preoperative and postoperative one-trial retrieval tests of set A (presented three times in every cycle of 6 d of training during initial acquisition), set B (presented twice), and set C (presented once). New learning is shown on the right. The total number of errors made to reach the criterion of 85% correct across three consecutive trials during postoperative acquisition of 100 novel unique scene discriminations (set D) for neurotoxic magnocellular MDmc and unoperated control (CON) monkeys is shown.

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