Optic radiation activity during sleep and waking

Possible mechanisms for reducing memory confusion during sleep

Confusion readily occurs in memory processes between patterns that overlap substantially. Possible mechanisms are considered that might operate in an automatic manner to reduce such confusion. One such mechanism is the recall of patterns in a distorted way, so that they are enriched with greater activity in distinctive elements of experienced patterns than in overlapping elements. Selective consolidation based on such enriched patterns would reduce confusion in long-term recall and might benefit discrimination learning. It is shown how automatic algorithms could achieve this through a process with two phases. In the first phase, somewhat analogous to slow-wave sleep, it is necessary for the normal tendency of the nervous system to learn correlations of associated activity to be disabled. The second phase must occur while the cells most active in the first phase are relatively inexcitable. Enriched patterns would be generated during this phase through recall, which might be triggered by bursts of activity such as occur in rapid eye movement sleep. Selective consolidation would take place during the second phase. If such processes do occur in the nervous system, it seems likely that they would have evolved to occur during sleep.

Doubly modifiable synapses: a model of short and long term auto-associative memory

Synapses that can be strengthened in temporary and persistent manners by two separate mechanisms are shown to have powerful advantages in neural networks that perform auto-associative recall and recognition. A multiplicative relation between the two weights allows the same set of connections to be used in a closely interactive way for short-term and long-term memory. Algorithms and simulations are described for the storage, consolidation and recall of patterns that have been presented only once to a network. With double modifiability, the short-term performance is dramatically improved, becoming almost independent of the amount of long-term experience. The high quality of short-term recall allows consolidation to take place, with benefits from the selection and optimization of long term engrams to take account of relations between stored patterns. Long-term capacity is greater than short-term capacity, with little or no deficit compared with that obtained with singly modifiable synapses. Long-term recall requires special, simply implemented, procedures for increasing the temporary weights of the synapses being used to initiate recall. A consolidation algorithm is described for improving long-term recall when there is overlap between patterns. Confusional errors are reduced by strengthening the associations between non-overlapping elements in the patterns, in a two-stage process that has several of the characteristics of sleep.

Lesion of the ponto-geniculo-occipital pathways in kittens. I. Effects on sleep and on unitary discharge of the lateral geniculate nucleus

Suppression of geniculate ponto-geniculo-occipital (PGO) waves was achieved in kittens by performing bilateral mesencephalic lesions of the PGO pathways. Sleep-wake parameters and the spontaneous unit activity in the lateral geniculate nucleus (LGN) were then chronically recorded during one month after the lesions. Whereas the states of vigilance remained normal, a significant reduction of the unitary discharge in the LGN during paradoxical sleep (PS) and particularly of its phasic component, was observed concomitantly with the suppression of PGO waves. It is concluded that phasic discharge of LGN neurons during PS is controlled by PGO-related mechanisms and that its suppression during the developmental period provides a model for studying its significance on brain maturation.

Relationship of geniculate and occipital PGO waves and the effects of nonvisual sensory activity

The nature of occipital PGO waves (REM) was addressed by comparing the occipital PGO waves measured at the marginal gyrus with the geniculate PGO waves and the occipital PGO waves "directly" transmitted to the occipital cortex. The directly transmitted PGO waves lack the first short positive-going spike that precedes the negative phase of the occipital PGO waves. The "directly" transmitted PGO wave was recorded from cats with either deafferented or excised LG nucleus. The "directly" transmitted PGO wave resembled pontine negative-going PGO wave more regarding amplitude and wave shape changes than the occipital PGO waves of intact cats. The ascending negativity of pontine PGO waves is indirectly transmitted through phasic increase of the local excitatory processes, more in the LG than in the occipital cortex. The PGO waves seem to be affected by endogenous and exogenous nonvisual processes, more in the LG than the occipital cells alone. The occipital PGO waves seem to result from the vectorial sum of geniculate and "directly" transmitted occipital PGO waves.