An examination of "transfer of learning" by nucleic Acid

The molecular memory code and synaptic plasticity: A synthesis

The most widely accepted view of memory in the brain holds that synapses are the storage sites of memory, and that memories are formed through associative modification of synapses. This view has been challenged on conceptual and empirical grounds. As an alternative, it has been proposed that molecules within the cell body are the storage sites of memory, and that memories are formed through biochemical operations on these molecules. This paper proposes a synthesis of these two views, grounded in a computational model of memory. Synapses are conceived as storage sites for the parameters of an approximate posterior probability distribution over latent causes. Intracellular molecules are conceived as storage sites for the parameters of a generative model. The model stipulates how these two components work together as part of an integrated algorithm for learning and inference.

The central importance of nuclear mechanisms in the storage of memory

The neurobiological nature of the memory trace (engram) remains controversial. The most widely accepted hypothesis at present is that long-term memory is stored as stable, learning-induced changes in synaptic connections. This hypothesis, the synaptic plasticity hypothesis of memory, is supported by extensive experimental data gathered from over 50 years of research. Nonetheless, there are important mnemonic phenomena that the synaptic plasticity hypothesis cannot, or cannot readily, account for. Furthermore, recent work indicates that epigenetic and genomic mechanisms play heretofore underappreciated roles in memory. Here, we critically assess the evidence that supports the synaptic plasticity hypothesis and discuss alternative non-synaptic, nuclear mechanisms of memory storage, including DNA methylation and retrotransposition. We argue that long-term encoding of memory is mediated by nuclear processes; synaptic plasticity, by contrast, represents a means of relatively temporary memory storage. In addition, we propose that memories are evaluated for their mnemonic significance during an initial period of synaptic storage; if assessed as sufficiently important, the memories then undergo nuclear encoding.

The First Annual Meeting of the Society for Neuroscience, 1971: Reflections Approaching the 50th Anniversary of the Society's Formation

The formation of the Society for Neuroscience in 1969 was a scientific landmark, remarkable for the conceptual transformation it represented by uniting all fields touching on the nervous system. The scientific program of the first annual meeting of the Society for Neuroscience, held in Washington, DC in 1971, is summarized here. By reviewing the scientific program from the vantage point of the 50th anniversary of the Society for Neuroscience, the trajectory of research now and into the future can be tracked to its origins, and the impact that the founding of the Society has had on basic and biomedical science is evident. The broad foundation of the Society was firmly cast at this first meeting, which embraced the full spectrum of science related to the nervous system, emphasized the importance of public education, and attracted the most renowned scientists of the day who were drawn together by a common purpose and eagerness to share research and ideas. Some intriguing areas of investigation discussed at this first meeting blossomed into new branches of research that flourish today, but others dwindled and have been largely forgotten. Technological developments and advances in understanding of brain function have been profound since 1971, but the success of the first meeting demonstrates how uniting scientists across diversity fueled prosperity of the Society and propelled the vigorous advancement of science.

RNA from Trained Aplysia Can Induce an Epigenetic Engram for Long-Term Sensitization in Untrained Aplysia

The precise nature of the engram, the physical substrate of memory, remains uncertain. Here, it is reported that RNA extracted from the central nervous system of Aplysia given long-term sensitization (LTS) training induced sensitization when injected into untrained animals; furthermore, the RNA-induced sensitization, like training-induced sensitization, required DNA methylation. In cellular experiments, treatment with RNA extracted from trained animals was found to increase excitability in sensory neurons, but not in motor neurons, dissociated from naïve animals. Thus, the behavioral, and a subset of the cellular, modifications characteristic of a form of nonassociative long-term memory (LTM) in Aplysia can be transferred by RNA. These results indicate that RNA is sufficient to generate an engram for LTS in Aplysia and are consistent with the hypothesis that RNA-induced epigenetic changes underlie memory storage in Aplysia.

Can memory exist outside of brain and be transferred? Historical review, issues & ways forward

Learning and memory are among the executive functions attributed to intelligent forms of life. Unfortunately, there is a lack of clear understanding regarding the underlying mechanisms governing these functions. Most of the modern day scientists attribute these functions solely to brain. However, in the latter half of last century, a number of reports suggested existence of extra-cranial memory and potential of its transfer between animals. Some have linked this phenomenon to RNA while others believed that peptides were responsible. The terms like "educated RNA" and "scotophobin" were coined. This atypical work involving flatworms, yeast RNA and scotophobin was received with deep skepticism and ultimately disregarded. However, the recent reproduction of some of this earlier work by scientists at Tufts University has reignited the debate on the mechanisms of learning and memory. Keeping this in view, we believe it is high time to summarize this historical work and discuss the possibilities to delineate these atypical claims. The objective is to incite the present day researchers to explore this opportunity under the perspective of newer advancements in science.

Rna and Memory: A Re-Evaluation of Present Data

Studies on the beneficial effects of yeast RNA treatment on learning and memory in senile patients and in animal experimentation are reviewed in this paper. Experimental evidence is cited showing that yeast RNA is not incorporated into brain tissue and does not increase brain synthetic activity. Thus the therapeutic effects of RNA treatment cannot be explained in direct relation to the hypothesis that RNA within the brain encodes memory information. Evidence for stimulant action of RNA, mediated by uric acid, its primary metabolite, is presented as the basis for an alternative theory which would explain RNA action in pharmacological terms.

Changes in brain structure during learning: fact or artifact? Reply to Thomas and Baker

In their review in this issue, Thomas and Baker question the validity of longitudinal human neuroimaging studies that have claimed to demonstrate structural plasticity. This commentary identifies problems with some of the arguments raised in their review and suggests that there is strong evidence, from both animal and human studies, that experience can alter brain structure.

Imaging learning: the search for a memory trace

Learning is associated with structural changes in the human brain that can be seen and studied by MRI. These changes are observed in gray matter and surprisingly also in white matter tissue. Learning a wide range of skills, from sports, computer games, music, and reading, to abstract intellectual learning, including classroom study, is associated with structural changes in appropriate cortical regions or fiber tracts. The cellular changes underlying modifications of brain tissue during learning include changes in neuronal and glial morphology as well as vascular changes. Both alterations in axon morphology and myelination are thought to contribute to white matter plasticity during learning but to varying degrees depending on age. Structural changes in white matter could promote learning by improving the speed or synchrony of impulse transmission between cortical regions mediating the behavior. Action potentials can stimulate oligodendrocyte development and myelination by at least three known mechanisms that involve signaling molecules between axons and oligodendrocytes, which do not require neurotransmitter release from synapses. Integrating information from cellular/molecular and systems-level research on normal cognitive function, development, and learning is providing new insights into the biological mechanisms of learning and the structural changes produced in the brain.

Georges Ungar and memory transfer

The idea that memories could be transferred from one organism to another by administration of a "trained" donor brain to a naive recipient seized both scientific and public attention in the 1960's and early 1970's. Georges Ungar was one of the earliest and strongest proponents of this idea, and he provided it extensive theoretical and experimental support. This paper reviews Ungar's work on memory transfer (and in particular on the scotophobin molecule), with an analysis of its successes and failures.

Memory and ribonucleic acid (RNA): transfer of an avoidance response

4 groups of rats were used to test the hypothesis that learning can be “transferred” by means of “ribonucleic” acid (RNA). The experimental group was injected with RNA obtained from the brains of rats conditioned to an avoidance response. The control group received no RNA. A second control group was given RNA which came from the brains of non-conditioned rats. The fourth group received RNA extracted from the muscles of conditioned rats. The results did not confirm the transfer hypothesis since no RNA facilitating effect on subsequent avoidance training was observed.

Interanimal "memory" transfer: results from brain and liver homogenates

Sixty mice received either shock or no shock in a shuttle box, or nonspecific stress in another apparatus. Brain and liver homogenates from these animals were then injected into 120 naive recipients, who were all tested in the shuttle box. Subjects receiving brain or liver from shocked or stressed donors had significantly higher latencies than control counterparts. These results are interpreted in terms of stress, rather than a memory transfer hypothesis.

Incubation effects in behavior induction in rats

Incubation (rest) periods interposed during donor training regimens significantly enhance the "memory transfer" effect reported by some investigators. When extracts from ihe brains of donor rats given interpolated rest during acquisition training were injected into recipient animals, statistically reliable and experimentally reproducible "memory transfer" effects were found.

Specificity of transfer of a learned response by intracisternal injection of brain extract from trained rats: negative findings

One group of rats was trained on a discrimination task while another group received no training. Brain extract containing RNA was prepared from the brains of these rats and injected intracisternally into naive rats. The naive rats were then retrained on the original discrimination task. No differences were found between the performances of the tats injected with “trained” extract, “untrained” extract, or saline solution.

Preparation and effect of different adjuvants on the immunogenic activity of mycobacterial ribosomal fraction

Several emulsified and two nonemulsified incomplete adjuvants were examined for their adjuvant activity by use of mycobacterial ribosomal fractions as a substrate. A good adjuvant is defined as one which produces a high immunological response with the ribosomal fraction in mice to infection with virulent tubercle bacilli. Freund's incomplete adjuvant, consisting of Aquaphor and heavy mineral oil, and Arlacel A plus hexadecane were the best adjuvants tested. Aquaphor plus light mineral oil and Arlacel A plus 7-n-hexyloctadecane were not quite as effective. Peanut oil was not satisfactory when emulsified with either Aquaphor or Arlacel A. A moderate degree of immunity was produced in mice vaccinated with ribosomal fraction mixed with aluminum hydroxide gel. Sodium alginate mixed with ribosomal fraction produced a low degree of immunity only with the highest vaccinating dose. It was found that the effectiveness of the emulsified type of adjuvant depended upon the method of preparation. Careful standardization of technique to produce uniform and complete emulsification was essential for maximal adjuvant activity using minimal vaccinating doses. A rapid and practical method of preparing emulsified adjuvants is given. The mode of action of incomplete adjuvants as employed in these experiments is discussed, and it is thought that they acted primarily by protecting the ribosomes from being inactivated by host ribonuclease before they were engulfed by the macrophages.

Facilitation of discrimination learning by injection of an RNA extract prepared from donor subjects

Naive rats given intraperitoneal injections of an extract prepared from the brains of either trained or untrained donor rats learned a position discrimination task in simple parallel alley runways significantly faster than original (uninjected) donor rats. Specific interanimal transfer, however, was not demonstrated as there was no statistically reliable difference between recipients of “trained brain” vs “untrained brain” extracts.

An attempt to transfer a position discrimination habit via RNA extracts

RNA extracted from trained and untrained (control) rats did not demonstrate statistically significant transfer of learning effects when injected intraperitoneally into naive recipient rats. Since the direction of the results consistently favored the “trained RNA extract” recipient, it is suggested that future investigation of biochemical transfer utilize more rigorous training for donor animals and larger RNA dosage levels for injections of recipient animals.