Learning deferred imitation of long spatial sequences

Dopamine neuronal loss contributes to memory and reward dysfunction in a model of Alzheimer’s disease

“…The hippocampal formation receives both cortical and sub-cortical inputs, the latter arriving mainly from the ventral tegmental area (VTA), locus coeruleus (LC), medial septal nucleus, raphe complex and the nucleus basalis of Meynert, all modulating hippocampal activity7891011. Pioneering neuropathological observations in post-mortem AD brain1213 demonstrated that the hippocampal formation and extrinsic (both cortical and sub-cortical) connections are disrupted at multiple levels, suggesting that the progressive structural alterations in the different brain areas may contribute to the worsening of memory and cognitive functions in AD patients.…”

A new test to detect impairments of sequential visuospatial memory due to lesions of the temporal lobe

“…Because order errors and explorations occurred only exceptionally in the present study (order errors: 2.5%; exploration errors: 2.7%), recall performance was assessed by the number of targets assigned. The learning progress was evaluated as the time course of the recall probability across trials, computed as the fraction of the number of assigned targets with respect to the number of targets per trial (20). Since these recall probabilities are subject to noise, its time course was approximated in each individual by a cumulative normal distribution with mean and standard deviation as fitted by a generalized linear regression with a probit link-function for the dependence of the recall probability on the trial number and the assumption of a binomial distribution of each recall probability.…”

“…The DILSS-task [19][20][21] was performed in trials consisting of a presentation-phase during which the subject only observed the target on the screen, followed by a reproduction-phase during which the subject pointed with the graphic pen to the memorized target locations on the blank screen. A full training session consisted of 25 repetitions of these presentation-reproduction pairs.…”

“…Here we only briefly describe its characteristic features and the results we obtained with it in our previous studies: 1) the length of the sequence (here 20) exceeds the capacity of the visuospatial working memory; 2) the spatial locations are continuously distributed and not constrained to a limited set as in the task of Tucker, Novelly [18]; 3) during sequence presentation, subjects are not allowed to move the motor effector (eye or hand); 4) the recall which alternates with sequence presentation has to be performed on a blank screen without intermediate feedback (a major difference from the serial reaction-time task); 5) the timing of the recall is not accelerated or constrained by an external trigger, but under the free control of the subject. Previous studies showed that the recall of sequences learned in this task is independent of the motor effector (pointing with eye or hand) and is retained for several days to weeks [20]. Compared to the serial reaction-time task with accelerated responses [22], DILSS shows a general lack of memory interference [21] and does not show typical features of implicit motor learning such as chunking [23] or error propagation between subsequent elements [24].…”

“…A sequential visuospatial memory is needed, for example, in landmark-based navigation, when a long sequence of visual cues is used to reconstruct a spatial path without representing its entire shape. Because of the apparent lack of sequential tasks on visuospatial memory, we developed in previous studies [19][20][21] a test for deferred imitation of long spatial sequences (DILSS) by either manual or ocular pointing movements. In this task, subjects acquire a very long sequence of target positions in a repeated succession of presentation and reproduction.…”