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June 30, 2015

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Rats may dream about finding treats

June 30, 2015
Courtesy of University College London
and World Science staff

When rats rest, their brains sim­u­late jour­neys to a de­sired fu­ture such as a tasty treat, new re­search finds.

Sci­en­tists mon­i­tored brain ac­ti­vity in rats, first as the an­i­mals looked at food in a place they could not reach, then as they rested in a sep­a­rate cham­ber, and fi­nally as they were al­lowed to walk to the food. 

The ac­ti­vity of spe­cial­ized brain cells in­volved in naviga­t­ion sug­gested that dur­ing the rest the rats sim­u­lated walk­ing to and from food that they had been un­able to reach, said the re­search­ers, from Uni­vers­ity Col­lege Lon­don.

The stu­dy, pub­lished in the jour­nal eLife, could help to ex­plain why some peo­ple with dam­age to a part of the brain called the hip­po­cam­pus are un­able to im­ag­ine the fu­ture, they added.

“Dur­ing ex­plora­t­ion, mam­mals rap­idly form a map of the en­vi­ron­ment in their hip­po­cam­pus,” said study co-author Hu­go Spiers. “Dur­ing sleep or rest, the hip­po­cam­pus re­plays jour­neys through this map which may help strength­en the mem­o­ry. It has been spec­u­lat­ed that such re­play might form the con­tent of dreams. Wheth­er or not rats ex­pe­ri­ence this brain ac­ti­vity as dreams is still un­clear, as we would need to ask them to be sure! Our new re­sults show that dur­ing rest the hip­po­cam­pus al­so con­structs frag­ments of a fu­ture yet to hap­pen. Be­cause the rat and hu­man hip­po­cam­pus are sim­i­lar, this may ex­plain why pa­tients with dam­age to their hip­po­cam­pus strug­gle to im­ag­ine fu­ture events.”

In the ex­pe­ri­ment, ro­dents were in­di­vid­ually placed on a straight track with a T-junc­tion ahead. A trans­par­ent bar­ri­er blocked ac­cess to the junc­tion as well as the left and right hand arms be­yond. One of the arms had food at the end, the oth­er was emp­ty. Af­ter see­ing the food the rats were put in a sleep cham­ber for an hour. Fi­nally af­ter the bar­ri­er was re­moved, the an­i­mals were re­turned to the track and al­lowed to run across the junc­tion and on to the arms.

Dur­ing the rest pe­ri­od, the da­ta showed that place cells that would lat­er pro­vide an in­ter­nal map of the food arm were ac­tive, ac­cord­ing to the in­ves­ti­ga­tors. Cells rep­re­sent­ing the emp­ty arm weren’t ac­tivated in this way. This in­di­cates that the brain was sim­u­lat­ing or pre­par­ing fu­ture paths lead­ing to a de­sired goal, the re­search­ers said.

“What’s really in­ter­est­ing is that the hip­po­cam­pus is nor­mally thought of as be­ing im­por­tant for mem­o­ry, with place cells stor­ing de­tails about loca­t­ions you’ve vis­it­ed,” said co-author Frey­ja Ólafs­dót­tir. “What’s sur­pris­ing here is that we see the hip­po­cam­pus plan­ning for the fu­ture, ac­tu­ally re­hears­ing to­tally nov­el jour­neys that the an­i­mals need to take in or­der to reach the food.”

The re­sults sug­gest that the hip­po­cam­pus plans routes that have not yet hap­pened as well as re­cord­ing those that have al­ready hap­pened, but only when there is a mo­tiva­t­ional cue such as food, the au­thors added. This may al­so imply that an­i­mals oth­er than hu­mans can im­ag­ine fu­ture events.

“What we don’t know at the mo­ment is what these neu­ral sim­ula­t­ions are ac­tu­ally for,” said co-author Cas­well Bar­ry. “It seems pos­si­ble this pro­cess is a way of eval­u­at­ing the availa­ble op­tions to de­ter­mine which is the most likely to end in re­ward, think­ing it through if you like. We don’t know that for sure though and some­thing we’d like to do in the fu­ture is try to es­tab­lish a link be­tween this ap­par­ent plan­ning and what the an­i­mals do next.”


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When rats rest, their brains simulate journeys to a desired future such as a tasty treat, new research finds. Scientists monitored brain activity in rats, first as the animals looked at food in a place they could not reach, then as they rested in a separate chamber, and finally as they were allowed to walk to the food. The activity of specialized brain cells involved in navigation suggested that during the rest the rats simulated walking to and from food that they had been unable to reach, said the researchers, from University College London. The study, published in the journal eLife, could help to explain why some people with damage to a part of the brain called the hippocampus are unable to imagine the future, they added. “During exploration, mammals rapidly form a map of the environment in their hippocampus,” said study co-author Hugo Spiers. “During sleep or rest, the hippocampus replays journeys through this map which may help strengthen the memory. It has been speculated that such replay might form the content of dreams. Whether or not rats experience this brain activity as dreams is still unclear, as we would need to ask them to be sure! Our new results show that during rest the hippocampus also constructs fragments of a future yet to happen. Because the rat and human hippocampus are similar, this may explain why patients with damage to their hippocampus struggle to imagine future events.” In the experiment, rodents were individually placed on a straight track with a T-junction ahead. A transparent barrier blocked access to the junction as well as the left and right hand arms beyond. One of the arms had food at the end, the other was empty. After seeing the food the rats were put in a sleep chamber for an hour. Finally after the barrier was removed, the animals were returned to the track and allowed to run across the junction and on to the arms. During the rest period, the data showed that place cells that would later provide an internal map of the food arm were active, according to the investigators. Cells representing the empty arm weren’t activated in this way. This indicates that the brain was simulating or preparing future paths leading to a desired goal, the researchers said. “What’s really interesting is that the hippocampus is normally thought of as being important for memory, with place cells storing details about locations you’ve visited,” said co-author Freyja Ólafsdóttir. “What’s surprising here is that we see the hippocampus planning for the future, actually rehearsing totally novel journeys that the animals need to take in order to reach the food.” The results suggest that the hippocampus plans routes that have not yet happened as well as recording those that have already happened, but only when there is a motivational cue such as food, the authors added. This may also imply that animals other than humans can imagine future events. “What we don’t know at the moment is what these neural simulations are actually for,” said co-author Caswell Barry. “It seems possible this process is a way of evaluating the available options to determine which is the most likely to end in reward, thinking it through if you like. We don’t know that for sure though and something we’d like to do in the future is try to establish a link between this apparent planning and what the animals do next.”