Side-box 9.3 Sleep and memory formation

A great deal of research continues into the link between sleep and consolidation, mostly supportive of the hypothesis. A collection of papers were published together in Nature near the end of 2005, and a major review by Walker and Stickgold in 2006.

Relatively direct evidence for the link has recently been claimed by Marshall et al. (2006); see also Stickgold (2006). They injected currents into the lateral frontal areas of human brain at low (0.75 Hz) frequencies to induce or enhance sleep-like oscillations in field potentials. If done just when slow-wave sleep was due to begin, this intervention enhanced the retention of declarative memory for previously learned lists of paired associates.

However, it is worth remembering that learning is obviously not confined to sleep, and can take place also in waking states (Foster and Wilson, 2006).

Section 9.4 and Side-box 9.6

In these sections, and in section 10.3.1, there is discussion of the relative effects of neural activity passing up versus down the several stages along the pathways of sensory processing. Some workers have suggested that the ascending sweep alone can give rise to perceptual experience, while others feel that it gives only primitive or ‘gist’ perception and the descending fibres are necessary for full, attentive completion of percepts. Now, Lamme (2006) has summarised arguments that recurrent processing just is neural basis of consciousness, whereas purely feedforward activity is not (see also the web update to Chapter 3). This applies within sensory areas alone (e.g. along the ventral stream of visual areas) or on a larger scale between the posterior and frontal lobes. Attention and many other cognitive functions however can occur in the absence of consciousness (cf. section 8.3).

References

Foster, D.J. and Wilson, M.A. (2006) Reverse replay of behavioural sequences in hippocampal place cells during the awake state. Nature 440, 680-683.

Lamme, V.A.F. (2006) Towards a true neural stance on consciousness. Trends in Cognitive Sciences 10, 494-501.

Marshall, L., Helgadóttir, H., Mölle, M. and Born, J. (2006) Boosting slow oscillations during sleep potentiates memory. Nature (in press; epub 5th November).

Stickgold, R. (2006) A memory boost while you sleep. Nature (in press; epub 5th November).

Various authors (2005) Waking up to the importance of sleep. Nature 437, 1207 and 1253-1289.

Walker, M.P. and Stickgold, R. (2006) Sleep, memory, and plasticity. Annual Review of Psychology 57, 139-166.