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We establish that long-term trace consolidation requires sleep within a restricted period shortly after learning. Undisturbed sleep is necessary for the stabilization of long-term memory, measured at the behavioral and neuronal levels, and of long-term but not short-term neuronal responsiveness to the training stimulus.

There is strong converging evidence that the intermediate and medial part of the hyperstriatum ventrale of the chick brain is a memory store for information acquired through the learning process of imprinting. Neurons in this memory system come, through imprinting, to respond selectively to the imprinting stimulus (IS) neurons and so possess the properties of a memory trace. Therefore, the responses of the intermediate and medial part of the hyperstriatum ventrale neurons to a visual imprinting stimulus were determined before, during, and after training. Of the total recorded population, the proportions of IS neurons shortly after each of two 1-h training sessions were significantly higher (approximately 2 times) than the pretraining proportion. However, Ϸ4.5 h later this proportion had fallen significantly and did not differ significantly from the pretraining proportion. Nevertheless, Ϸ21.5 h after the end of training, the proportion of IS neurons was at its highest (approximately 3 times the pretraining level). No significant fluctuations occurred in the proportions of neurons responding to the alternative stimulus. In addition, nonmonotonic changes were found commonly in the activity of 230 of the neurons tracked individually from before training to shortly after the end of training. Thus the pattern of change in responsiveness both at the population level and at the level of individual neurons was highly nonmonotonic. Such a pattern of change is not consistent with simple models of memory based on synaptic strengthening to asymptote. A model is proposed that accounts for the changes in the population responses to the imprinting stimulus in terms of changes in the responses of individual neurons.

loss of muscle strength is associated with poorer functional ability and both are associated with reduced HRQoL. The reduction in HRQoL is considerable in the physical functioning domain. Cause and effect was not established but studies need to be undertaken to evaluate the benefits of strength training, functional activity training or increased participation in life.

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The responsiveness of neurons in a region of the chick brain involved in the learning process of imprinting, the right intermediate and medial hyperstriatum ventrale (right IMHV), has been investigated in unanaesthetized, trained and untrained chicks. The results demonstrate that neuronal responsiveness in this region reflects a variety of behavioural consequences of imprinting and is markedly altered as a result of the learning process. Groups of chicks (nine in each group) were either dark-reared or trained (imprinted) by exposure to a rotating red box or a rotating blue cylinder. Recordings of single or small groups of neurons were subsequently made from 156 sites in the right IMHV while the 2-day-old chicks were free to move in a running wheel. There was a highly significant increase in the proportion of sites responsive to the stimulus used to train the birds compared to the proportion responsive to that stimulus in dark-reared birds (30 and 9% respectively). These changes were found when either the red box or the blue cylinder was used to train the bird, the changes being similar for both stimuli. There was also a significant increase in the mean magnitude of the change in neuronal activity on stimulus presentation for the training stimulus compared to the same stimulus when not used in the bird's training. No significant effects of the training experience of the chicks were found upon either the magnitude of evoked activity or the proportion of sites responsive to a rotating stuffed jungle fowl or the sound of the maternal call. The presence of the training stimulus was selectively signalled by the response at certain sites. At other sites there was response generalization across stimulus shape or colour. A comparison with results for the left IMHV demonstrates both similarities and differences in neuronal responsiveness between the two regions. In both regions imprinting selectively enhances neuronal responsiveness to the training stimulus. However, for trained birds the mean proportion of sites responding to whichever of the red box or the blue cylinder was not used in the bird's training was significantly lower in the right than the left IMHV. These results are discussed in relationship to previously reported asymmetries in the response of the right and left IMHV regions to imprinting. A model is introduced to explain the physiological findings. The effects of training on right IMHV neuronal function are consistent with a long-term role for this region in the recognition memory of imprinting.

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