We examined the effects of noise on acquisition and retention of the spatial memory task in equal and unequal context in adult male rats. The natural noise in Azadi football stadium was recorded and measured by sound level meter instrument and set in high (HI), moderate (MI), and low (LI) intensities, 86, 64, and 47 decibels A (dbA), respectively. Rats were trained in Morris water maze (MWM) for 3-consecutive-day program and at day 4 visible and probe tests were done under one of the above noise intensities. The retention was evaluated at day 7 on the basis of equal and unequal noise exposure situation. Escape latency, traveled distance, and swimming speed were recorded and used for subsequent analysis. Our results showed significant increases in the escape latency and traveled distance by increasing the noise intensity during acquisition period, and also retention test in equal noise situation. Furthermore, retention test in the group that was under HI noise during both training period and retention test escape latency and traveled distance compared to the groups which was under HI noise during training period and LI or MI noise during retention test (HI-LI or HI-MI).
Noise is one
of the problems which affects some aspects of human life. For example, noise
impairs human task performance most likely in the case of unexpected bursts of
noise presented during tasks, whether it involves the continuous intake of new
information [
Studies on the short-term effects of imposed noise on school-age
children’s performance in classroom environments have found no effects of a
range of noise levels on writing task performance [
Some theories explaining the effects of noise are primarily based
on the researcher's perception of the role of adaptation [
However, different kinds and levels of noise can have various effects on retention test. The present study was performed to investigate this idea that whether various intensities of noise can act as differential positive and negative impacts on acquisition and retention of a spatial memory task in equal; when the intensity of noise during training period is the same as exposed noise intensity during retention performance task, and unequal noise contextual situations in rats.
Adult male albino Wister rats (12 weeks old), weighting 250–300 gr, were obtained from the breeding colony of the Pasteur Institute of Iran. They were housed four per cage in a temperature and light-controlled room under 12 hours: 12 hours light-dark cycle (light at 07:00 am) with free access to water and food. Experiments were carried out in a room where only the MWM was placed in standard conditions and took place at 13:00–16:00.
We measured intensity of noise obtained from a football stadium with sound level meter (B&K 2250, UK) instrument, when the stadium was full of spectators (about 100 000 people). The intensity of noise was about 105 dbA in an extremely noisy situation, and about 95 dbA in moderate situation, and also 69 dbA in silence times. At first, we recorded this natural sound from football stadium and compared to the hearing system of rats, then we set the intensity of noise for high and moderate situations in 86 dbA and 64 dbA. We regulated the acoustic system in these intensities by Cool-Edit 2000 Software (designed by Gold soft company, UK) at a stable frequency.
The MWM task was consisted of a
dark circular pool (140 cm in diameter, 55 cm height) filled with water (
The spatial memory task was defined as finding the hidden platform in the MWM. All rats were given a daily session of two blocks (each block consisted of 4 trials) with 5 minutes interval between blocks for 3 days in the training period. During all experiments, the platform was located in a fixed position in the middle of SW quadrant. Each trial involved placing the rat in the pool, close to and facing the wall in one of the four equal quadrants (North, South, East, or West). Rats were allowed to swim freely until they found the platform. If a rat failed to find the platform within 90 seconds, the experimenter placed the rat on it. The intertrial interval was 30 seconds, during which the rat remained on the platform. The rat was taken directly from the platform to the new starting point which was changed from trial to trial in a quasirandom order. So each starting point was used once in each session of 4 trials. All animals were exposed to the defined noise in their group (as described below) during training period and also probe, visible, and retention tests.
We divided rats into 3 groups: low-intensity
noise group (LI = control) was trained under natural noise (47 dbA) (
The data analyzed by one-way
analysis of variance (ANOVA), followed by post hoc Tuky's test and also we used
The aim of this experiment was to determine the effect of low-intensity (LI) noise exposure during acquisition period and retention test on MWM performance. In this experiment, rats were trained in LI noise for 3 training days according to the procedure. Visible and probe tests were held in day 4. Retention test was performed under equal (LI) and two unequal (MI and HI) noise conditions. It should note since environmental sounds in the experimental room were similar to LI noise intensity (approximately 47 dbA), so we used the group under LI-exposed noise during both training period and retention test (LI-LI) as the control group.
The aim of this experiment was to determine the effect of MI noise exposure during acquisition period and retention test on MWM performance. In this experiment, rats were trained in MI noise for 3 training days according to the procedure. Visible and probe tests held in day 4. Retention test was performed under equal (MI) and two unequal (LI and HI) noise conditions.
The aim of this experiment was to determine the effect of HI noise exposure during acquisition period and retention test on MWM performance. In this experiment, rats were trained in HI noise for 3 training days according to the procedure. Visible test and probe tests held in day 4. Retention test was performed under equal (HI) and two unequal (LI and MI) noise conditions.
Our results were based on the data which was acquired in acquisition period and retention tests in equal and unequal noise situations. The escape latency, traveled distance, and swimming speed were recorded. In all experiments, the swimming speed had no significant differences. So we do not report details of speed results here.
Figure
Effects of various
intensities of noise during training period on escape latency in day 1–3 and visible
test (day 4). *
For traveled distance, there were significant differences at
day 1 [
Effects of various
intensities of noise during training period on traveled distance in day 1–3 and visible
test (day 4). *
There were no significant
differences between the results of day 1 to 3 in LI noise (Figures
Different effects of
noise exposure on escape latency. (a) Equal (LI-LI) and unequal, moderate (LI-MI)
and high (LI-HI) intensities, and retention tests in LI training group; (b) equal
(MI-MI) and unequal, low (MI-LI) and high (MI-HI) intensities, and retention
tests in MI training group; (c) equal (HI-HI) and unequal, low (HI-LI) and
moderate (HI-MI) intensities, and retention tests in HI training group; (d) equal retention tests for LI, MI, and HI
training groups. *
Different effects of
noise exposure on traveled distance. (a) Equal (LI-LI) and unequal, moderate
(LI-MI) and high (LI-HI) intensities, and retention tests in LI training group;
(b) equal (MI-MI) and unequal, low (MI-LI) and high (MI-HI) intensities, and retention
tests in MI training group; (c) equal (HI-HI) and unequal, low (HI-LI) and
moderate (HI-MI) intensities, and retention tests in HI training group; (d) equal
retention tests for LI, MI, and HI training groups. *
There were significant differences between the results of
day 1 to 3 in exposed MI noise (Figures
There were significant differences between the results of
day 1 to 3 in exposed HI noise (Figures
Figures
In this study, adult male rats
treated with different intensities of exposed noise displayed memory performance
impairments by increase in intensity of noise (47, 64, and 86 dbA). In training
period, it was significant difference between performance of groups in day 1
and day 2. Also this difference was shown in days 2 and 3 between HI with MI
and LI in escape latency and traveled distance. The longest time and traveled distance
to find the platform during acquisition period was seen at HI group. It is possible
that learning process might be impaired by high-intensity noise [
The present results in
experiment 3 showed that retention test in equal situation after exposure to
high-intensity noise (HI-HI) in training period caused less latency and traveled
distance rather than unequal retention in moderate noise (HI-MI). This finding
supports the “test-training context law” described that retention can
be better in equal contexts [
In experiment 4, it did not
show significant difference between LI-LI and MI-MI groups in equal retention
test. It may be associated with “power of training law” [
In general, it seems that the interaction between training period and noise intensity might interfere with the level of performance in special retention test. We concluded that when a group trains at the special noise intensity in training period, it will get adaptation with the situation, and then it will have lower performance in other intensities at the retention tests, even at the lower intensities. So, it might be better to train at the equal noise intensity, maybe adapt with this external disruptive operant and decrease its influences.
The authors would like to thank R. Maes and S. A. Stanfeld for sending their articles and Mr. Akbary, Ms. Majlesi, Ms. bozorgmehr, and Dr. Sepehrian for their comments on the manuscript.