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1

Efficiency of the forebrain commissures: memory for stimuli seen by the other hemisphere

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Kavcic V., Doty R. W.

Acta Neurobiologiae Experimentalis

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2002

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vol. 62

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issue 4

235-242

EN

How well will one cerebral hemisphere recognize items viewed initially via the other? Nonverbalizable images or words were presented to one visual field and memory for them tested in the same or the other visual field. The initially viewing hemisphere subsequently had no secure advantage in accuracy, and only for images was there a 30-ms (ca 3%) penalty in reaction time for viewing with the ?other? hemisphere. Interhemispheric mnemonic communication is thus highly reliable. At longer retention intervals (1-2 min vs. 4-30 s, with accumulating added stimuli), however, recognition of words was asymmetric as to hemisphere, in that initial viewing via the right hemisphere was subsequently (and paradoxically) much better recognized via the left (other) hemisphere than was the converse situation. This suggests that the initial engram with right hemispheric viewing of words ultimately becomes established in the left, and that the right has less accurate access to a previous ?left hemispheric view?.

2

Unity from duality

100%

Doty R. W.

Acta Neurobiologiae Experimentalis

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2003

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vol. 63

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issue 3

163-170

EN

When, in the primeval sea, creatures first began to crawl, 'right' and 'left' came into being, yielding neuronal nets to control response to the sidedness of stimuli. In the half billion years of moving and sensing, two brains have evolved, the right and the left; and human experience now shows them to be roughly equivalent, potentially independent, conscious entities. This dramatic fact is evidenced by 'split-brain' patients and by numerous cases of therapeutic removal of either hemisphere. Equally dramatic, of course, is that there is not the slightest sign of this duality in everyday experience, the right and left visual fields are seamlessly knit, and cross purpose is absent in the moment to moment operation of the two cerebral hemispheres. This unity is constantly synthesized by the 100,000,000 fibers passing from each hemisphere to the other; the vastness of that interchange emphasized upon comparison with the mere 1,000,000 fibers conveying all the visual world from each eye. With the large distances in the human brain some 100+ ms may commonly transpire for one hemisphere to send to and receive a response from the other. Efficiency thus demands that most neuronal calculation occur within rather than between hemispheres, thereby promoting differences in the characteristic capabilities of each alone, i.e., 'hemispheric specialization'. Despite this there is a bewildering bilaterality of activation revealed by fMRI for most cognitive tasks. In the absence of the forebrain commissures brainstem systems can be shown, in macaques, also to participate in the unification of behavioral result from the actions of the separated hemispheres. The system favors synthesis from congruent (visual) input to the two hemispheres; but in the face of incompatible hemispheric input, the two hemispheres are able to work out an accommodation in their control of subcortical systems.

3

Frontal cortex, laterality, and memory: encoding versus retrieval

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Kavcic V., Zhong J., Yoshiura T., Doty R. W.

Acta Neurobiologiae Experimentalis

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2003

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vol. 63

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issue 4

337-350

EN

The cerebral hemispheres differ in their capabilities and response to verbal versus nonverbal visual material. A priori, it might thus be expected that the right hemisphere would be best activated during a mnemonic task with fMRI when using nonverbalizable images, and the left hemisphere with verbal material. However, previous psychological tests had shown a high degree of similarity in measures of memory for these disparate items. It was thus hypothesized that extensive commonality in the areas activated would prevail when this previously tested material was employed with fMRI. Six subjects underwent fMRI with four types of trials in blocks: fixating; passively viewing 12 words and 12 nonverbalizable images; endeavoring to remember (encoding) another set of 12 words and images; endeavoring to recognize (retrieve) previously viewed words or images. Passive viewing produced small islands of activation in left versus right frontal cortex for words and images, respectively. Endeavoring to remember enlarged the areas of activation and produced some bilaterality. Retrieval greatly augmented activation as well as bilaterality, and some 20% of the activated frontal volume was shared by words and images. Thus, on the one hand, the distribution of activation upon retrieval differed substantially for words versus images, but on the other, as predicted, there was considerable commonality. Predominant laterality of activation in some areas shifted between encoding and retrieval (HERA), importantly involving different regions for words versus images. Of course, processes other than memory per se are undoubtedly involved in these distributions of fMRI activation in frontal cortex, yet the nature of the to-be-remembered items is clearly a major factor, in accord with the asymmetric lateralization in their basic representation.

4

Konorski and conditional reflexes. A historical summary and an addendum

88%

Doty R. W.

Acta Neurobiologiae Experimentalis

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2006

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vol. 66

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issue 1

91-97

EN

There have been four major pioneers from Eastern Europe in the neuroscientific study of memory and learning: Pavlov, Bekhterev, Beritashvili and Konorski. The thinking of each evolved with the progress of neuroscientific knowledge throughout the world, and save for Pavlov, each encountered governmental opposition to their views. Among the clues largely overlooked in their examination of conditional reflexes was the fact that the animal appreciates not only its own appetitive state but its immersion in the experimental setting. The latter in itself must require considerable, ongoing neuronal activity to sustain it. There is also the question as to whether ?motivation' is an essential feature for the formation of conditional connections; and in cases where it is seemingly absent, as in recognition memory, the processes that underlie the astonishing efficacy of such memory formation remain almost wholly obscure. Finally, it is remarked that the cerebral cortex, as initially supposed, may indeed be the governing locus, even of such simple effects as habituation.

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Efficiency of the forebrain commissures: memory for stimuli seen by the other hemisphere

Unity from duality

Frontal cortex, laterality, and memory: encoding versus retrieval

Konorski and conditional reflexes. A historical summary and an addendum