Dark chocolate contains Epicatechin (Epi) flavanol. Researchers have found that (Lymnaea) snails experienced enhanced memory formation following exposure to Epi as observed through monitoring the snails’ aerial respiratory behavior. Additionally, exposure to Epi has also been shown to relieve stress which hindered learning new behaviors and recalling behavioral changes thereby restoring memory enhancement. Such benefits are also applicable to humans where there is a correlation between intake of flavanols in dark chocolate with the improvement of cognitive ability and reduction of cognition deterioration, especially in older people. In a new study conducted by Hotchkiss Brain Institute Cumming School of Medicine, scientists investigated how long Epi’s enhancing effect persisted if applied before and if there be an effect if applied after a behavioral change from training is induced on the snails. Formation of long term memory (LTM) in snails after training persists for at least 24 hours.
There is a period of time where learning is encoded into memory after training, also known as the consolidation period. In Lymnaea, the consolidation period lasts for about an hour, during which memory formation can be altered by either enhancing or suppressing it using different stressers. Recently, it was discovered that a thermal stressor’s effect on enhancing memory formation in Lymnaea could continue for days before training or if applied directly after training. Thus in this study, scientists directly test whether Epi would have similar effects as that of a thermal stresser, exposing snails to Epi: 1) 1 hour before training, 2)immediately after training, or 3)after training would result in enhanced memory formation, keeping the concentration of Epi constant with that of previous experiments (15mg l -1)and for the same period of time (40 mins). Snails received a 0.5 hour training session (TS) and a 0.5 hour memory test (MT) 24 hours later. In the training session, to operantly condition aerial respiratory behavior, snails were placed in pond water with inadequate water supply and every time they attempted to open their pneumonstome (breathing pore) to respire aerially, they received a tactile stimulus to the pneumonstome which causes it to close.
By comparing how many times the pneumostome tried to open during TS and MT, it can be determined whether LTM was established by observing the significance of decrease in the number of times the pneumstome attempted opening in MT as compared to that in TS. The first group of snails were exposed to pond water containing Epi for 40 minutes 1 hour before the training and were returned to their home aquarium where they underwent TS and MT. The results as seen from figure 1A where there was no significant decrease in the number of attempted pneumostrome openings, thus LTM was not established. The second group of snails was placed into pond water containing Epi immediately after undergoing training. They were then taken back to their home aquarium where they underwent the MT 24 hours later. The results as shown in Figure 1B displayed a significant decrease in the number of attempted pneumostome openings in MT as compared to TS. Therefore, long term memory was established. The third group of snails was exposed to pond water containing Epi 1 hour after TS and underwent MT 24 hours later. There was no significant decrease number of attempted openings in MT from that of TS as seen in Figure 1C hence no LTM was established. Cumulatively, these findings show that pretreating or delaying Epi exposure to snails would not cause memory formation enhancement induced by Epi.
Rather, it is through training snails in Epi or immediate exposure to Epi after training which enhances the formation of memory. Similar to how a cold block will only effectively block memory formation if applied immediately after training and not an hour later, it can be derived that the consolidation period of active bodily processes where memory formation starts at once after training and lasts up till an hour. Scientists also acknowledged that there are numerous varying mechanisms in enhancing memory formation including predator detection, heat shock proteins and DNA methylation. However, scientists are still uncertain of the necessity of these processes for Epi-induced memory enhancement or how Epi induces memory enhancement. Ongoing experiment shows that Epi alters the activity of neuron RPeD1 involved with memory formation, reconsolidation, extinction and forgetting with the possibility of Epi altering neurons or pathways involved with aerial respiratory behavior. In summary, it can be derived from this study that exposing snails to Epi 1 hour before or after training is inadequate to bring about enhancement of memory. Epi is able to effectively induce memory formation enhancement if the snails is exposed to Epi in the consolidation period, .immediately after training.
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