Non-spatial acquisition and retention deficits following small excitotoxic lesions within the hippocampus in monkeys

• Published in: Neuroscience Vol. 107; no. 2; pp. 239 - 248
• Main Authors: Ridley, R.M., Hardy, A., Maclean, C.J., Baker, H.F.
• Format: Journal Article
• Language: English
• Published: Oxford Elsevier Ltd 01-01-2001; Elsevier
• Subjects: Anatomical correlates of behavior; Animals; Behavioral psychophysiology; Biological and medical sciences; Callithrix; conditional learning; Conditioning, Classical; Dentate Gyrus - pathology; Discrimination Learning; Excitatory Amino Acid Agonists; Female; Fundamental and applied biological sciences. Psychology; hippocampus; Hippocampus - pathology; Male; Microscopy, Electron; monkey; N-Methylaspartate; Psychology. Psychoanalysis. Psychiatry; Psychology. Psychophysiology; Retention (Psychology); AP, anterioposterior; monkey; PBS, phosphate-buffered saline; hippocampus; DNMS, delayed (non)-matching to sample; ANOVA, analysis of variance; UTHSCSA, University of Texas Health Science Center at San Antonio; conditional learning; WGTA, Wisconsin General Test Apparatus; Learning; Vertebrata; Mammalia; Acquisition process; Animal; Central nervous system; Monkey; Primates; Lesion; Hippocampus; Brain (vertebrata)
• ISSN: 0306-4522; 1873-7544
• DOI: 10.1016/S0306-4522(01)00358-X

Marmoset monkeys with excitotoxic lesions confined to cornu ammonis subfields 1–3, subiculum and pre-subiculum, but sparing the entorhinal cortex, were impaired on retention and learning of conditional object–choice discriminations. For each of these discriminations, the monkeys were required to choose one of two objects depending on which of two patterned backgrounds was used on each trial. Two styles of order of trial presentation were used: ‘random’ presentation which maximised the degree of interference between trials, and ‘runs’ presentation which was intended to encourage the monkeys to learn each component of the discrimination separately. Before surgery monkeys found the discriminations more difficult to learn when the trials were presented in the ‘runs’ style than when presented in the ‘random’ style suggesting that the task is best learnt by applying a conditional rule. After surgery a significant ‘group×style’ interaction indicated that the ‘runs’ style was especially difficult for the lesioned monkeys.
From these results we suggest that the hippocampus is involved in learning about and remembering non-spatial, conditional relations between objects.