Cognitive impairment in a young marmoset reveals lateral ventriculomegaly and a mild hippocampal atrophy: a case report

Abstract

The number of studies that use the common marmoset (Callithrix jacchus) in various fields of neurosciences is increasing dramatically. In general, animals enter the study when their health status is considered satisfactory on the basis of classical clinical investigations. In behavioral studies, variations of score between individuals are frequently observed, some of them being considered as poor performers or outliers. Experimenters rarely consider the fact that it could be related to some brain anomaly. This raises the important issue of the reliability of such classical behavioral approaches without using complementary imaging, especially in animals lacking striking external clinical signs. Here we report the case of a young marmoset which presented a set of cognitive impairments in two different tasks compared to other age-matched animals. Brain imaging revealed a patent right lateral ventricular enlargement with a mild hippocampal atrophy. This abnormality could explain the cognitive impairments of this animal. Such a case points to the importance of complementing behavioral studies by imaging explorations to avoid experimental bias.

Figure 1. Learning performances in the SD task.

Number of daily sessions (a) and those of 100 trials (b) necessary to reach the learning criterion.

Figure 2. Response strategies in the SD task.

The occurrence of the LSh (a) and the ChSh sub-strategies (b) in the learning and learnt phases. Error bars represent the 95% bias-corrected and accelerated bootstrap confidence intervals (P < 0.05). *Significant.

Figure 3. Learning performances in the DMTP task.

(a) Individual learning curves. Data were calculated after discarding correction trials (see methods). (b) Number of sessions to reach the learning criterion. Data are represented as median and interquartile intervals. The red square represents the performance of the PathC.

Figure 4. Evolution of the animals’ response strategies in the DMTP task.

(a) The Win-Stay sub-strategy in the learning phase. (b) The Lose-Shift sub-strategy in the DMTP task as a function of the delay. Error bars represent the bias-corrected and accelerated bootstrap confidence intervals (P < 0.006). *Significant.

Figure 5. Evolution of the response strategies in the randomized-delay step in the DMTP task.

(a) WSt sub-strategy. (b) LSh sub-strategy. (c) ChSh strategy. Error bars represent the bias-corrected and accelerated bootstrap confidence intervals (P < 0.006). *Significant.

Figure 6. MRI images.

MRI T1 and T2 weighted scans showing the contrast between the abnormal ventricular enlargement (arrow) in the PathC (a,b) and another animal (c)