Rat Spatial Memory Tasks Adapted for Humans:
Characterization in Subjects with Intact Brain and Subjects with
Medial Temporal Lobe Lesions
V. D. BOHBOT1, R. JECH2,
E. RŮŽIČKA2, L. NADEL1, M. KALINA3,
K. STĚPÁNKOVÁ3, J. BUREŠ4
1Psychology Department and ARL-NSMA, University of
Arizona, Tucson, 2Department of Neurology, First
Medical Faculty, Charles University, 3Department of
Neurology, Hospital Na Homolce and 4Institute of
Physiology, Czech Academy of Sciences, Prague, Czech republic
Summary
In the present paper we describe five tests, 3 of which were
designed to be similar to tasks used with rodents. Results
obtained from control subjects, patients with selective
thermo-coagulation lesions to the medial temporal lobe and
results from non-human primates and rodents are discussed. The
tests involve memory for spatial locations acquired by moving
around in a room, memory for objects subjects interacted with,
or memory for objects and their locations. Two of the spatial
memory tasks were designed specifically as analogs of the Morris
water task and the 8-arm radial-maze tasks used with rats. The
Morris water task was modeled by hiding a sensor under the
carpet of a room (Invisible Sensor Task). Subjects had to learn
its location by using an array of visual cues available in the
room. A path integration task was developed in order to study
the non-visual acquisition of a cognitive representation of the
spatial location of objects. In the non-visual spatial memory
task, we blindfolded subjects and led them to a room where they
had to find 3 objects and remember their locations. We designed
an object location task by placing 4 objects in a room that
subjects observed for later recall of their locations. A
recognition task, and a novelty detection task were given
subsequent to the recall task. An 8-arm radial-maze was
recreated by placing stands at equal distance from each other
around the room, and asking subjects to visit each stand once,
from a central point. A non-spatial working memory task was
designed to be the non-spatial equivalent of the radial maze.
Search paths recorded on the first trial of the Invisible Sensor
Task, when subjects search for the target by trial and error are
reported. An analysis of the search paths revealed that patients
with lesions to the right or left hippocampus or parahippocampal
cortex employed the same type of search strategies as normal
controls did, showing similarities and differences to the search
behavior recorded in rats. Interestingly, patients with lesions
that included the right parahippocampal cortex were impaired
relative to patients with lesions to the right hippocampus that
spared the parahippocampal cortex, when recall of the sensor was
tested after a 30 min delay (Bohbot et al. 1998). No differences
were obtained between control subjects and patients with
selective thermal lesions to the medial temporal lobe, when
tested on the radial-maze, the non-spatial analogue to the
radial-maze and the path integration tasks. Differences in
methodological procedures, learning strategies and lesion
location could account for some of the discrepant results
between humans and non-human species. Patients with lesions to
the right hippocampus, irrespective of whether the right
parahippocampal cortex was spared or damaged, had difficulties
remembering the particular configuration and identity of objects
in the novelty detection of the object location task. This
supports the role of the human right hippocampus for spatial
memory, in this case, involving memory for the location of
elements in the room; learning known to require the hippocampus
in the rat.
Key
words
Morris water maze • 8-arm radial-maze • Space • Object •
Navigation • Hippocampus • Parahippocampal Cortex • Human • Rat
• Neuropsychology
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