Positive and Negative Memories Are Split Up in Brains of Mice

Summary: A new study reports on how positive and negative memories for smells, taste and experiences are located in different areas of the amygdala in mice.

Source: RIKEN.

Like broccoli and ice cream on a toddler’s plate, the brain also keeps nice and nasty information in separate places. Within the amygdala, an important memory center in the brain, pleasant experiences, tastes, and smells are confined to the back of the basolateral nucleus (BLA), while unpleasant ones are stored at the front. These anterior and posterior regions also interact in a push-pull manner, regulating behaviors tied to negative and positive stimuli, respectively. As reported on October 17 in Nature Neuroscience, these opposing neurons in the amygdala are not only physically separated but also genetically distinct.

While there is previous evidence for a positive/negative division in the brains of mice and fruit flies for smell and taste memories, the link from this split to positive and negative behaviors had not been established. Anterior and posterior BLA neurons are also capable of disrupting expected behaviors if they are turned on or off with optogenetic light stimulation, according to the new study from the RIKEN-MIT Center for Neural Circuit Genetics.

To identify the ‘negative’ and ‘positive’ neurons, researchers exposed male mice to either footshocks or the company of a female mouse. These specific experiences leave their mark in the amygdala in the form of higher expression levels of the gene c-Fos, a marker of neural activity. The activated neurons were genetically profiled, revealing two distinct genetic markers–Rpso2 for negative neurons and Ppp1r1b for positive neurons. Rspo2 was observed almost exclusively in the anterior BLA, while expression of the Ppp1r1b gene was concentrated in the posterior BLA. These spatially distinct positive and negative neurons differed in their size, shape, and electrical properties as well. The positive neurons were activated when mice were exposed to pleasant smells and water rewards, while negative neurons became active in response to pain and unpleasant smells.

Moreover, anterior and posterior neurons not only responded to the value of rewards, but were crucial for associated negative and positive behaviors, respectively. Mice were trained either to respond to footshocks by freezing in place (the negative behavior) or to perform a light-cued nose poke to receive water (the positive behavior). Using optogenetics, a method for manipulating genetically tagged cells with light, the researchers could weaken these behaviors, simply by targeting either the anterior or posterior BLA with precise bursts of light while the mice were trained.

Image shows a mouse brain.
While there is previous evidence for a positive/negative division in the brains of mice and fruit flies for smell and taste memories, the link from this split to positive and negative behaviors had not been established. NeuroscienceNews.com image is for illustrative purposes only.

Finally, the positive and negative neurons could even interfere with how well mice learned the associated positive and negative behaviors. The expected freezing behavior was reduced by light stimulation of positive neurons during the footshock training, and activation of negative neurons impaired the mice in the water reward task. These neurons could effectively drown out the positive or negative meaning of powerful external stimuli like water or shocks, and this is achieved through mutual inhibitory neural signaling between the anterior, or negative, and posterior, or positive BLA. The basolateral amygdala thus has an important role in associating negative and positive stimuli with appropriate behaviors.

About this memory research article

Source: Adam Phillips – RIKEN
Image Source: NeuroscienceNews.com image is for illustrative purposes only.
Original Research: Abstract for “Antagonistic negative and positive neurons of the basolateral amygdala” by Joshua Kim, Michele Pignatelli, Sangyu Xu, Shigeyoshi Itohara & Susumu Tonegawa in Nature Neuroscience. Published online October 17 2016 doi:10.1038/nn.4414

Cite This NeuroscienceNews.com Article

[cbtabs][cbtab title=”MLA”]RIKEN. “Positive and Negative Memories Are Split Up in Brains of Mice.” NeuroscienceNews. NeuroscienceNews, 17 October 2016.
<https://neurosciencenews.com/memory-behavior-mouse-brain-5305/>.[/cbtab][cbtab title=”APA”]RIKEN. (2016, October 17). Positive and Negative Memories Are Split Up in Brains of Mice. NeuroscienceNews. Retrieved October 17, 2016 from https://neurosciencenews.com/memory-behavior-mouse-brain-5305/[/cbtab][cbtab title=”Chicago”]RIKEN. “Positive and Negative Memories Are Split Up in Brains of Mice.” https://neurosciencenews.com/memory-behavior-mouse-brain-5305/ (accessed October 17, 2016).[/cbtab][/cbtabs]


Abstract

Antagonistic negative and positive neurons of the basolateral amygdala

The basolateral amygdala (BLA) is a site of convergence of negative and positive stimuli and is critical for emotional behaviors and associations. However, the neural substrate for negative and positive behaviors and relationship between negative and positive representations in the basolateral amygdala are unknown. Here we identify two genetically distinct, spatially segregated populations of excitatory neurons in the mouse BLA that participate in valence-specific behaviors and are connected through mutual inhibition. These results identify a genetically defined neural circuit for the antagonistic control of emotional behaviors and memories.

“Antagonistic negative and positive neurons of the basolateral amygdala” by Joshua Kim, Michele Pignatelli, Sangyu Xu, Shigeyoshi Itohara & Susumu Tonegawa in Nature Neuroscience. Published online October 17 2016 doi:10.1038/nn.4414

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