Methods of Assessment of Learning and Memory
Methods of Assessment of Learning and Memory
Methods of Assessment of Learning and Memory
),
National Institute of Mental Health and Neuro Sciences, Bangalore, India. 2004:145-151.
Among the various functions of the brain, one Currently several of the mechanisms underlying
of the most interesting and puzzling one is the such a magnificent phenomenon as memory have
ability to acquire new information and store them been understood. However, many of them remain to
for future retrieval. Learning is defined as be completely resolved. Animal models are useful in
behavioral modification through experiences or deciphering this complex machinery at molecular,
conditioning and when this persists it is termed cellular and systems level. Several of the CNS
memory. Memory can be broadly classified into disorders are often associated with impairment in
declarative and non-declarative memory (Figure cognitive functions. Alzheimer’s disease and ageing,
1) (Milner et al., 1998). Declarative memory for example have a primary impact on learning and
answers the question ‘what’, i.e. it is possible to memory, and other diseases such as Parkinson’s
verbally declare this type of memory. Memory of disease, bipolar depression, schizophrenia, and many
facts and events are examples of declarative other neurological disorders have been demonstrated
memory. Declarative memory can be further to have a secondary deficit in learning and memory.
classified into episodic and semantic memory. There are drugs available for the treatment of these
Episodic memory is memory of past and personally memory disorders, but clinical improvement is far
encountered events. The knowledge for the from satisfaction. Presently, the pathophysiological
meaning of words and how to use them is phrased mechanisms underlying these disorders have not
as semantic memory. Non-declarative (or been clearly understood and it is imperative that new
procedural) memory answers the question ‘how’ drugs that would be more useful be developed.
and is not stored with respect to time and place. Experimental paradigms of learning and memory are
Skills, habits and priming are examples of non- very enlightening in both elucidation of the
declarative memory. Priming is change in the pathophysiology and development of new
ability to detect or identify objects as the result of medications for the treatment of learning and
recent encounters, for example, Mys in Mysore. memory disorders.
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Paradigms of Learning and Memory different conditioning paradigms are
Broadly the paradigms can be based on either summarized in Table 1.
avoidance conditioning or maze training. Table 1: Summary of the different types of tasks
Avoidance conditioning can be further classified used to assess learning and memory (Brioni et al.,
into active and passive conditioning. The 1997; Reddy, 1997)
1. Step-down task
2. Step-through task
Passive avoidance
3. Two compartment task
4. Up-hill avoidance
1. Y maze
2. T maze
3. Radial arm maze (RAM)
Mazes 4. Water maze (WM)
5. Figure 8 maze
6. Complex maze
7. Stone maze
8. Battig maze
The hippocampus has been shown to be an important structure involved in learning and memory. There have been
many mazes that have been used to test hippocampal function (Table 1). The radial arm maze (RAM) and water maze
(WM) are perhaps the most used among them. A few of the various mazes that are used are depicted in Figure 2.
METHODOLOGY
I. Operant Conditioning
The operant conditioning apparatus consists
of a rodent test chamber (Skinner’s box), pellet
dispenser, sound attenuating chamber and a
control unit. The test chamber contains two
stainless steel response levers (5 x 4cm each) at a
height of 6cm from the floor, located both on the
left and right side (termed left and right lever
respectively) on one wall of the chamber. A food
hopper (5 x 3cm) is located in between the two
levers at the floor level. Each lever can be pressed
passively by a weight of about 7-8g. The chamber
Figure 2. Different mazes employed to study learning is connected to a solid food dispenser. Food
and memory (Reddy, 1997). pellets (approx. 45mg) are delivered to the
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feeding tray (food hopper) from the pellet Operant conditioning has been extensively used
dispenser through a plastic tube once lever is in our lab as a learning paradigm, to study
pressed. The test chamber and the pellet dispenser neuronal plasticity and as a model to understand
are kept in a sound proof box so as to avoid the the role of different areas in brain’s function.
external disturbances (Bures et al., 1983). Increased dendritic arborisation and spine density
was demonstrated following operant conditioning
Procedure during the brain growth spurt (Mahajan and
Rats are semi starved for 48hrs to motivate them Desiraju, 1988). Operant conditioning was found
towards food reward. On subsequent days 5-8 gm sensitive to detect functional deficits following
of food is provided after the test so as to maintain exposure to several environmental toxins like lead
the body weight at 85% of its initial weight, (Kumar and Desiraju, 1992), mercuric chloride
throughout the experimental period. (Lakshmana et al., 1993), endosulfan (Lakshmana
and Raju, 1994), arsenic (Nagaraja and Desiraju,
Acquisition (learning) test 1994), and metanil yellow (Nagaraja and Desiraju,
The training/shaping period consists of 30min 1993). It has been used as a model to understand
session per day for three days. After three days of the effect of subordination stress on brain
training session, the rats are subjected to 15 min biochemistry (Dhingra et al., 1996; Dhingra et al.,
test session for seven days. The number of lever 1997). The role of subiculum (Govindaiah et al.,
press responses per session is recorded. 1997; Nutan and Meti, 2000), fornix
(Yoganarasimha and Meti, 1999)and substantia
Learning criterion: To assess the acquisition
of the operant learning task, the criterion is set nigra – ventral tegmental area (SN-VTA)
in such a way that the rats should reach 75% of (Yoganarasimha et al., 1998) in brain’s function
the maximum lever press response of normal has been examined using operant conditioning
control rats. paradigm. Furthermore, operant conditioning has
been used to demonstrate the capability of intra
Retention (Memory) test cranial self-stimulation (ICSS) to facilitate learning
(Yoganarasimha et al., 1998) and bring about
Retention test can be carried out, 48h, 72h or
functional reversal following fornix lesion
7 days after the acquisition phase of the operant
(Yoganarasimha and Meti, 1999). Thus, operant
conditioning. Here the rats are subjected to one
conditioning is a powerful test to evaluate learning
trial and the number of pedal presses is
calculated. and memory.
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