The role of sleep in the consolidation of auditory input

The role of sleep in the consolidation of auditory input

A scientific literature review

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Erwin Blanco San Martín

This paper has been designed and compiled as a pre requisite to pass the Integrated

advanced communicative competences of English language, September 2013.



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Introduction

Since the very moment we hear a sound we can discriminate whether it is human

speech or a tone, and also it is possible to identify whether it is new or already known.

What is the internal functioning of the auditory cortex? , Does the sleep play any role in

memorizing new auditory information? Do we share the same memory systems to store any

event or knowledge? To start off we might first take a glance at the scientific knowledge

about brain anatomy.

The theory of multiple memory systems was based a long time on behavioral

experiments without a biological support reinforcing the findings. Packard, M. G., Hirsh,

R., & White, N. M. (1989) developed a reliable research based on experimental tests to

prove the existence of anatomically distinct memory systems. The experiments consisted on

selecting two groups of rats to which different kind of brain lesions were applied, the first

type involved deep fimbria-fornix (hippocampus region) damage and the second involved

disruptive lesions in the caudate area. The tests consisted of a win-stay radial maze

designed to probe the long term memory of rats in getting food and a win-shift radial maze

intended to probe the working memory. A third group of rats was added in order establish a

control sample, the results were as follows: In the win-stay test the rats impaired at caudate

nucleus visited the arms more times than the fornix and control group, in addition the

fornix group was the fastest in memorizing and getting the food. On the other hand, in the

win-shift maze, the fornix group had the highest score of errors in comparison with the

control and caudate groups.



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It can be drawn as a result that at mammals are endowed with at least two kinds of

memory systems and that are related to both specific parts of the brain and to specific

abilities.

When we first learned a new word by ear -without reading-, how much does it take

to integrate it in our mental lexicon? Dumay, N., & Gaskell, M. G. (2007) taking

advantage of the theory that states that during auditory word recognition the

phonologically-close words compete to be retrieved from our mental lexicon (Gaskell,

M. G., & Dumay, N., 2003), conducted a research to measure the word-competition effect

across different time lapses, including sleep periods.

The experiment consisted of 25 male English speakers divided into 2 groups. Each

group learned word series consisting of a known word and two phonologically similar

competitors, for instance: Cathedral followed by cathedruce and cathedruke. Immediately

after the test, then 12 and 24 hours after, the participants took a word free recall test and a

recognition test. The results evidenced a similar performance in both groups at the first test,

conversely 12 hours after; the PM group (Who slept) outperformed far in latency of

response and word recall tests in comparison to the AM group. The explanation for the

results accounts for an enhanced consolidation as a result of the sleeping period for the PM



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group, finding that is reinforced by other studies based on the consolidating effect of sleep

in word recall (Plihal & Born (1997). Furthermore 24 hours after, the score of both tests

were almost even, why? Because at that point both groups had already had a sleeping

period that resulted into effective consolidation.

Comparable results registered a research aiming at measuring the influence of sleep

on auditory learning conducted by Gaab, N., Paetzold, M., Becker, M., Walker, M. P., &

Schlaug, G. (2004). The method consisted on exposing subjects to sine wave tones

spanning from 41-64 Hz. Those subjects that had a sleep period after the experiment shown

an increased enhancement in tone recognition in comparison to the group that experienced

a lapse of wakefulness, however the former group improved almost up to the same level of

the sleeping group after the natural sleeping period when tested one day after. In conclusion

regardless to the hour of learning the sleeping process will benefit with consolidation to

either group.



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It is clear according to the overwhelming evidence mentioned before that the human

memory system is divided into other subsystems that underlie to the classic differentiation

of declarative and non declarative memory (Squire, L.R., 1987)

Knowing that sleep has a substantial role in the acquisition and codification of

auditory lexicon the question that remains is: What is the algorithm that the auditory cortex

executes when matching and auditory stimulus with a lexicalized auditory element?,

Goldinger, (1996) conducted a complex investigation where around 100 university students

were exposed to spoken words uttered by different voices. The results can be synthesized in

these findings: First the auditory cortex is able to divide meaning and voice details such as

frecuency, (Purves, D., Augustine, G. J., Fitzpatrick, D., Katz, L. C., LaMantia, A. S.,

McNamara, J. O., & Williams, S. M , 2001), second, the episodic memory is able to retain

surface details such tone and pitch, third, that in word recognition the subjects were able to

identify the already learned words versus new ones even in presence of noise. An important



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variable to point out is that the less voices they heard, the more words they recognized in

long terms test.

The human auditory cortex. (A) Diagram showing the brain in left lateral view, including the depths of the lateral sulcus,

where part of the auditory cortex occupying the superior temporal gyrus normally lies hidden. The primary auditory cortex (A1) is shown

in blue; the surrounding belt areas of the auditory cortex are in red. (B) The primary auditory cortex has a tonotopic organization, as

shown in this blowup diagram of a segment of A1.Purves, Dale. "The Human Auditory Cortex." Sinauer Associates. U.S. National

Library of Medicine, 18 Jan. 0000. Web. 15 Sept. 2013

Further than the conceptual certainty that sleep is crucial for auditory consolidation,

the last question that remains is what bio-electro-chemical changes does sleep trigger in

order to consolidate new information?, Cantero, J. L., Atienza, M., Salas, R. M., &

Dominguez-Marin, E. (2002), investigated changes in the brain electrical activity patterns

during human sleep after a long period of continuous auditory stimulation. The aim of the

research was to asses any modification in the electrical activity (recorded by EEG) as result

of a prolonged auditory input during previous wakefulness. The sample to apply the

experiment consisted of eight volunteer subjects that were exposed to 4 different auditory

patterns for 6 hours in different frequencies, ranging from 300Hz to 8000Hz, in order to



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ensure the activation of different neuronal groups in the auditory cortex. The subjects were

equipped with EEG electrodes to measure electrophysiological changes during sleep.

The results of the experiment presented a massive calcium entry provoked by the

excitation–inhibition input patterns (See image below), an increased spectral power and

larger wave amplitude during SWS sleep in those regions that are related to auditory

input and processing, namely, temporal cortex and parietal cortex, however it was disclosed

that stimulation over the left ear did not correlate coherently with an enhanced activity in

the right brain hemisphere, it could be due to the different capacities of the hemispheres in

processing the sounds and speech (Sapher & Levanthal 1978) & (Van Lancker & kreiman,

1978). No changes were noticed during REM sleep period. Considering the variations of

electrical patterns there are two explanations that account for this surplus of spectral power

and wave amplitude: The first accounts for a homeostatic response due to overstimulation

of auditory neural networks, the second, stands for a novel experience-dependant cortical

reorganization (learning process). In either cases SWS is a critical for such synaptic

reorganization, in addition the former explanation might also rely on the first to thrive.



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As a brief synthesis of the state of the art in the role of sleep in the consolidation of

auditory input, it is possible to assert that mammals are endowed with different anatomical

and functional memory systems, also that the sleep plays a key role in the acquisition of

new auditory lexical items that are integrated during SWS sleep period. Regarding to

physiological changes, it has been clear that the SWS sleep involves surplus of electrical

activity and a homeostatic release of neurotransmitters (Calcium, CA2+) nevertheless this

cortical reorganization is only triggered by previous auditory-cortex overstimulation.

Extension: 1.150 words, without considering image footers and references.

References

Cantero, J. L., Atienza, M., Salas, R. M., & Dominguez-Marin, E. (2002). Effects of

prolonged waking-auditory stimulation on electroencephalogram synchronization

and cortical coherence during subsequent slow-wave sleep.The Journal of

neuroscience, 22(11), 4702-4708.

Dumay, N., & Gaskell, M. G. (2007). Sleep-associated changes in the mental representation

of spoken words. Psychological Science, 18(1), 35-39.



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Gaab, N., Paetzold, M., Becker, M., Walker, M. P., & Schlaug, G. (2004). The influence of

sleep on auditory learning: a behavioral study. Neuroreport, 15(4), 731-734.

Gaskell, M. G., & Dumay, N. (2003). Lexical competition and the acquisition of novel

words. Cognition, 89(2), 105-132.

Goldinger, S. D. (1996). Words and voices: episodic traces in spoken word identification

and recognition memory. Journal of Experimental Psychology: Learning, Memory,

and Cognition, 22(5), 1166.

Packard, M. G., Hirsh, R., & White, N. M. (1989). Differential effects of fornix and caudate

nucleus lesions on two radial maze tasks: evidence for multiple memory

systems. The Journal of neuroscience, 9(5), 1465-1472.

Plihal, W., & Born, J. (1997). Effects of early and late nocturnal sleep on declarative and

procedural memory. Journal of Cognitive Neuroscience, 9(4), 534-547.

Purves, D., Augustine, G. J., Fitzpatrick, D., Katz, L. C., LaMantia, A. S., McNamara, J.

O., & Williams, S. M. (2001). The auditory system.



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Safer, M. A., & Leventhal, H. (1977). Ear differences in evaluating emotional tones of

voice and verbal content. Journal of Experimental Psychology: Human Perception

and Performance, 3(1), 75.

Squire, L. R. (1987). Memory and brain. Oxford University Press.

Van Lancker, D., & Kreiman, J. (1987). Voice discrimination and recognition are separate

abilities. Neuropsychologia, 25(5), 829-834.

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The role of sleep in the consolidation of auditory input