Rats Dream of the Future

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Rats dream of the future, scientists tell us after implanting electrodes into the captives’ brains, following their dreams as they unfolded, recording them, studying them, finding that they were shaped by the individual's goals and desires and were centered in things she or he wished for. Then they killed the dreamers and dissected their brains.

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About the study:
https://www.newscientist.com/article/dn27788-rats-dream-about-the-places-they-wish-to-go/#.VY1C2WPJWL0

Journal reference:
https://elifesciences.org/articles/06063

Image: Arathrael Photography/Getty

 

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Article

Rats dream about the places they wish to go
26 June 2015
By Clare Wilson

Do you dream of where you’d like to go tomorrow? It looks like rats do.

When the animals are shown a food treat at the end of a path they cannot access and then take a nap, the neurons representing that route in their brains fire as they sleep – as if they are dreaming about running down the corridor to grab the grub.

“It’s like looking at a holiday brochure for Greece the day before you go – that night you might dream about the pictures,” says Hugo Spiers of University College London.

Like people, rats store mental maps of the world in their hippocampi, two curved structures on either side of the brain. Putting electrodes into rats’ brains as they explore their environment has shown that different places are recorded and remembered by different combinations of hippocampal neurons firing together.

These “place cells” fire not only when a rat is in a certain location, but also when it sleeps, as if it is dreaming about where it has been in the past.

Spiers’s team wondered whether this activity during sleep might also reflect where a rat wants to go in future. They placed four rats at the bottom of a T-shaped pathway, with entry to the top bar of the T blocked by a grille. Food was placed at the end of one arm, in a position visible to the animals.

Next they encouraged the rats to sleep in a cosy nest and recorded their hippocampus activity with about 50 electrodes each as they rested. Finally they put the rats back into the maze, but now with the grille and the treat removed.

As expected, the animals scampered along the arm where they had seen the food, with their place cells firing in a pattern corresponding to the new route. Crucially, these same cells had fired while the rats were asleep – unlike those that encoded the route to the other arm. “It suggests we construct our mental maps a little bit by looking, and then pad them out more by doing,” says Spiers.

Picturing the future
David Redish of the University of Minnesota in Minneapolis says this shows that rats’ dreams can be shaped by their goals. “It’s not just reflecting some baseline activity; it depends on the animals’ desires,” he says.

he work supports the idea that the hippocampus helps us to imagine the future, as well as encoding our memories of the past. Some people with damage to their hippocampi have problems imagining future events with any richness or detail.

Spiers admits that we cannot know for sure whether the rats were dreaming, or even if the rats were just having a peaceful rest rather than sleeping. But previous work in humans has suggested that brain activity while we snooze does reflect the content of our dreams.

In one experiment, people slept inside a brain scanner and were then woken up and asked to describe their dreams. The brain patterns observed when they dreamt of specific items matched the activity recorded when participants were shown the same items while conscious.

Researchers have also been able to alter the dreams of mice, a bit like in the film Inception. When electrodes stimulated brain areas that signal reward as the animals dreamed about a certain place, they were more likely to go to that spot when awake.

Journal reference: eLife, DOI: 10.7554/eLife.06063

Magazine issue 3028 , published 4 July 2015

Read more: https://www.newscientist.com/articl...out-the-places-they-wish-to-go/#ixzz61aWZC9T7

 

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Abstract

Hippocampal place cells construct reward related sequences through unexplored space

1. H Freyja Ólafsdóttir
   
   ,
2. Caswell Barry,
3. Aman B Saleem,
4. Demis Hassabis,
5. Hugo J Spiers
   

1. University College London, United Kingdom

Short Report Jun 26, 2015

elife Digest

As an animal explores an area, part of the brain called the hippocampus creates a mental map of the space. When the animal is in one location, a few neurons called ‘place cells’ will fire. If the animal moves to a new spot, other place cells fire instead. Each time the animal returns to that spot, the same place cells will fire. Thus, as the animal moves, a place-specific pattern of firing emerges that scientists can view by recording the cells' activity and which can be used to reconstruct the animal's position.

After exploring a space, the hippocampus may replay the new place-specific pattern of activity during sleep. By doing so, the brain consolidates the memory of the space for return visits. Recent evidence now suggests that these mental rehearsals—or internal simulations of the space—may begin even before a new space has been explored.

Now, Ólafsdóttir, Barry et al. report that whether an animal's brain simulates a first visit to a new space depends on whether the animal anticipates a reward. In the experiments, rats were allowed to run up to the junction in a T-shaped track. The animals could see into each of the arms, but not enter them. Food was then placed in one of the inaccessible arms. Ólafsdóttir, Barry et al. recorded the firing of place cells in the brain of the animals when they were on the track and during a rest period afterwards. The rats were then allowed onto the inaccessible arms, and again their brain activity was recorded.

In the rest period after the rats first viewed the inaccessible arms, the place cell pattern that would later form the mental map of a journey to and from the food-containing arm was pre-activated. However, the place cell pattern that would become the mental map of the other inaccessible arm was not activated before the rat explored that area. Therefore, Ólafsdóttir, Barry et al. suggest that the perception of reward influences which place cell pattern is simulated during rest. An implication of these findings is that the brain preferentially simulates past or future experiences that are deemed to be functionally significant, such as those associated with reward. A future challenge will be to determine whether this goal-related simulation of unvisited spaces predicts and is needed for behaviour such as successful navigation to a goal.

https://doi.org/10.7554/eLife.06063.002

 

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Introduction

We investigated whether the presence of an inaccessible goal in an unvisited portion of an environment was sufficient to elicit pre-activation (‘preplay’) of hippocampal place cell sequences that will subsequently represent runs through the unvisited environment. To this end, we recorded from ensembles of place cells (O'Keefe and Dostrovsky, 1971) (4 rats, 37–66 place cells each, 212 cells in total) while rats ran along a T-shaped track (Figure 1—figure supplement 1, Table 1) with visible yet inaccessible arms (Figure 1A)—RUN1. One arm (counter balanced between animals) was subsequently cued with food while the animal remained on the track—GOAL-CUE. During a rest period before RUN1 (REST1) and after GOAL-CUE (REST2), spiking events—periods of 300 ms or less, where at least 15% of cells were active (Foster and Wilson, 2006; Diba and Buzsaki, 2007)—were analysed. These spiking events were associated with significantly higher power in the ripple spectrum (80–250 Hz) than other comparable periods (Figure 1—figure supplement 2). To investigate whether paths on the cued and uncued arms were preplayed we assessed the match between the order in which cells fired during spiking events and during future runs on the arms (RUN2, Figure 1—figure supplement 3). Specifically, we computed the rank-order correlations between spiking events and sequences of place cells active on the arms, referred to as templates (Lee and Wilson, 2002; Foster and Wilson, 2006; Diba and Buzsaki, 2007; Dragoi and Tonegawa, 2011) (Figure 1—figure supplement 4). Preplay events were identified as those with either a significant positive or negative correlation—a two-tailed test, each tail tested at the 97.5% level. These preplay events were found to exhibit higher power in the ripple spectrum than non-significant spiking events (Figure 1—figure supplement 2). To establish significance at the population level, the proportion of preplay events measured was compared to a null distribution generated by calculating correlations between place cell templates and shuffled sequences from events (see Figure 1B–C).

See the article for the table and for the Results, Discussion, References, etc
https://elifesciences.org/articles/...KeMLygqUO6CHBtHzdJ44W40JcxEWfcRp9RSaqSeVYO-u4