Difficulties in retrieval multiplication facts: The case of interference to reconsolidation.

OBJECTIVES: Many students have difficulties in retrieving multiplication facts from memory. The aim of the present study was to test the difficulty in retrieval of multiplication facts from the perspective of the reconsolidation of long-term memory phase, which has been found to be sensitive to interferences. METHODS: Students learned multiplication facts and then received a reminder, which led to reactivation and reconsolidation. After the reminder, additional multiplication facts (interference) were learned and memory was tested. RESULTS: Students who received both a reminder and interference during reconsolidation showed no significant improvement in retrieving multiplication facts from memory, whereas Students who received either a reminder or additional multiplication facts (interference) exhibited a better performance in retrieval. CONCLUSIONS: These results indicate, for the first time, that the reconsolidation phase is sensitive to interferences in mathematical declarative memory content. The findings indicate additional possible causes for difficulties in retrieval of multiplication facts in class.

Nitric oxide and histamine signal attempts to swallow: A component of learning that food is inedible in Aplysia.

Memory that food is inedible in Aplysia arises from training requiring three contingent events. Nitric oxide (NO) and histamine are released by a neuron responding to one of these events, attempts to swallow food. Since NO release during training is necessary for subsequent memory and NO substitutes for attempts to swallow, it was suggested that NO functions during training as a signal of attempts to swallow. However, it has been shown that NO may also be released in other contexts affecting feeding, raising the possibility that its role in learning is unrelated to signaling attempts to swallow. We confirmed that NO during learning signals attempts to swallow, by showing that a variety of behavioral effects on feeding of blocking or adding NO do not affect learning and memory that a food is inedible. In addition, histamine had effects similar to NO on learning that food is inedible, as expected if the transmitters are released together when animals attempt to swallow. Blocking histamine during training blocked long-term memory, and exogenous histamine substituted for attempts to swallow. NO also substituted for histamine during training. Histamine at concentrations relevant to learning activates neuron metacerebral cell (MCC). However, MCC activity is not a good monitor of attempts to swallow during training, since the neuron responds equally well to other stimuli. These findings support and extend the hypothesis that NO and histamine signal efforts to swallow during learning, acting on targets other than the MCC that specifically respond to attempts to swallow.

Nitric oxide induces aspects of egg-laying behavior in Aplysia.

Aplysia egg laying is a complex behavior requiring synchronized activity in many organs. Aspects of the behavior are synchronized via the direct effects of peptide bag cell neurohormones and via stimuli arising during the behavior. Stimuli synchronizing egg laying were examined by treating A. fasciata with a nitric oxide (NO) donor. NO elicited normal appetitive and consummatory behaviors leading to the deposition of cordons containing egg capsules without eggs. The sites at which NO acts were investigated. The latency to egg deposition in response to a NO donor was shorter than that in response to other stimuli, consistent with NO acting at downstream sites from those affected by the other stimuli. The NO donor does not act on neurons in the head ganglia presynaptic to the bag cells or on the bag cells. Ligating the small hermaphroditic duct connecting the gonad to the accessory genital mass blocked egg laying in response to bag cell homogenates, but not in response to exogenous NO, indicating that NO does not act on the gonad. NO is released by transport of eggs along the small hermaphroditic duct, and NO directly acts on the accessory genital mass which packages eggs. NO also acts at a second site, independent of the effect on the accessory genital mass. A NO donor activates appetitive behaviors that normally precede egg laying even in A. californica that are unable to lay eggs.

Nitric oxide signals that aplysia have attempted to eat, a necessary component of memory formation after learning that food is inedible.

Inhibiting nitric oxide (NO) synthesis during learning that food is inedible in Aplysia blocks subsequent memory formation. To gain insight into the function of NO transmission during learning we tested whether blocking NO synthesis affects aspects of feeding that are expressed both in a nonlearning context and during learning. Inhibiting NO synthesis with L-NAME and blocking guanylyl cyclase with methylene blue decreased the efficacy of ad libitum feeding. D-NAME had no effect. L-NAME also decreased rejection responses frequency, but did not affect rejection amplitude. The effect of L-NAME was explained by a decreased signaling that efforts to swallow are not successful, leading to a decreased rejection rate, and a decreased ability to reposition and subsequently consume food in ad libitum feeding. Signaling that animals have made an effort to swallow is a critical component of learning that food is inedible. Stimulation of the lips with food alone did not produce memory, but stimulation combined with the NO donor SNAP did produce memory. Exogenous NO at a concentration causing memory also excited a key neuron responding to NO, the MCC. Block of the cGMP second-messenger cascade during training by methylene blue also blocked memory formation after learning. Our data indicate that memory arises from the contingency of three events during learning that food is inedible. One of the events is efforts to swallow, which are signaled by NO by cGMP.

Circadian modulation of complex learning in diurnal and nocturnal Aplysia.

Understanding modulation of memory, as well as the mechanisms underlying memory formation, has become a key issue in neuroscience research. Previously, we found that the formation of long-term, but not short-term, memory for a nonassociative form of learning, sensitization, was modulated by the circadian clock in the diurnal Aplysia californica. To define the scope of circadian modulation of memory, we examined an associative operant learning paradigm, learning that food is inedible (LFI). Significantly greater long-term memory of LFI occurred when A. californica were trained and tested during the subjective day, compared with animals trained and tested in the subjective night. In contrast, animals displayed similar levels of short-term memory for LFI when trained in either the subjective day or night. Circadian modulation of long-term memory for LFI was dependent on the time of training, rather than the time of testing. To broaden our investigation of circadian modulation of memory, we extended our studies to a nocturnal species, Aplysia fasciata. Contrary to the significant memory observed during the day with the diurnal A. californica, A. fasciata showed no long-term memory for LFI when trained during the day. However, A. fasciata demonstrated significant long-term memory when trained and tested during the night. Thus, the circadian clock modulates memory formation in phase with the animals' activity period. The results from our studies of circadian modulation of long-term sensitization and LFI suggest that circadian modulation of memory formation may be a general phenomenon with potentially widespread implications for many types of long-term learning.

Long-term memory requires polyADP-ribosylation.

PolyADP-ribose-polymerase 1 is activated in neurons that mediate several forms of long-term memory in Aplysia. Because polyADP-ribosylation of nuclear proteins is a response to DNA damage in virtually all eukaryotic cells, it is surprising that activation of the polymerase occurs during learning and is required for long-term memory. We suggest that fast and transient decondensation of chromatin structure by polyADP-ribosylation enables the transcription needed to form long-term memory without strand breaks in DNA.

Nitric oxide and memory.

Nitric oxide (NO) is widely used in neural circuits giving rise to learning and memory. NO is an unusual neurotransmitter in its modes of release and action. Is its association with learning and memory related to its unusual properties? Reviewing the literature might allow the formulation of a general principle on how NO and memory are related. However, other than confirming that there is indeed a strong association between NO and memory, no simple rules emerge on the role of NO in learning and memory. The effects of NO are not associated with a particular stage or form of memory and are highly dependent on species, strain, and behavior or training paradigm. Nonetheless, a review does provide hints on why NO is associated with learning and memory. Unlike transmitters acting via receptors expressed only in neurons designed to respond to the transmitter, NO is a promiscuous signal that can affect a wide variety of neurons, via many molecular mechanisms. In circuits giving rise to learning and memory, it may be useful to signal some events via a promiscuous messenger having widespread effects. However, each circuit will use the promiscuous signal in a different way, to achieve different ends.

Nitric oxide is necessary for multiple memory processes after learning that a food is inedible in aplysia.

Nitric oxide (NO) signaling was inhibited via N(omega)-nitro-L-arginine methyl ester (L-NAME) during and after training Aplysia that a food is inedible. Treating animals with L-NAME 10 min before the start of training blocked the formation of three separable memory processes: (1) short-term, (2) intermediate-term, and (3) long-term memory. The treatment also attenuated, but did not block, a fourth memory process, very short-term memory. L-NAME had little or no effect on feeding behavior per se or on most aspects of the animals' behavior while they were being trained, indicating that the substance did not cause a pervasive modulation or poisoning of many aspects of feeding and other behaviors. Application of L-NAME within 1 min after the training had no effect on short- or long-term memory, indicating that NO signaling was not needed during memory consolidation. Treating animals with the NO scavenger 2-phenyl-4,4,5,5-tetramethyl-imidazdine-1-oxy-3-oxide before training also blocked long-term memory. Memory was not blocked by D-NAME, or by the simultaneous treatment with L-NAME and the NO donor S-nitroso-N-acetyl-penicillamine, confirming that the effect of L-NAME is attributable to its effect as a competitive inhibitor of L-arginine for NO synthase in the production of NO rather than to possible effects at other sites. These data indicate that NO signaling during training plays a critical role in the formation of multiple memory processes.