Mirror of insight: Mice show glimpses of self-recognition

summary: Mice exhibit similar self-recognition behavior when seeing their reflections in mirrors. This behavior appears under specific conditions: familiarity with mirrors, socialization with similar-looking mice, and visible markings on their fur.

The study also identifies a subset of neurons in the hippocampus that are essential for this self-recognition-like behavior. These findings provide valuable insights into the neural mechanisms underlying self-recognition, a previously obscure aspect of neurobehavioral research.

Key facts:

1. Conditional self-recognition: Mice showed increased grooming behavior in response to visible white ink spots on their fur while viewing mirrors, but only when they were familiar with the mirrors and socialized with similar-looking mice.
2. Neural mechanisms identified: A specific population of neurons in the ventral hippocampus was found to be integral to this mirror-induced self-recognition-like behavior.
3. Social and sensory influences: The study highlights the importance of social experiences and sensory cues in the development of self-recognition abilities, expanding our understanding of how these factors contribute to neural development.

source: Cell press

The researchers report December 5 in the journal nervous cells Mice show self-recognition-like behavior when they see themselves in a mirror. When the researchers marked the foreheads of black-furred mice with a spot of white ink, the mice spent more time brushing their heads in front of a mirror, trying to wash off the ink spot.

However, the mice showed this self-recognition-like behavior only if they were already accustomed to the mirrors, if they had socialized with other mice that looked like them, and if the inkblot was relatively large.

The team identified a subset of neurons in the hippocampus that are involved in developing and storing this visual self-image, providing a first glimpse into the neural mechanisms underlying self-recognition, something that was previously a black box in neurobehavioral research.

“To form episodic memory, for example, for the events of our daily lives, brains form and store information about where, what, when and who, the most important element of which is subjective or state information,” says neuroscientist and lead author Takashi. Kitamura of the University of Texas Southwestern Medical Center.

“Researchers typically examine how the brain encodes or recognizes others, but the self-information aspect is less clear.”

The researchers used the mirror test to see if mice were able to detect a change in their appearance, in this case, a spot of ink on their foreheads. Because the ink also provides a tactile stimulus, the researchers tested black-furred mice with black and white ink.

Although the mirror test was originally developed to test consciousness in different species, the authors note that their experiments only show that mice can detect a change in their appearance, but that does not necessarily mean they are “self-aware.”

They found that mice could indeed detect changes in their appearance, but only under certain conditions. Mice that were familiar with mirrors spent significantly more time brushing their heads (but not other parts of their bodies) in front of the mirror when they were marked with 0.6 cm long dollops of white ink.² Or 2 cm².

However, the mice did not engage in increased head grooming when the ink was black – the same color as their fur – or when the ink mark was small (0.2 cm).²), even if the ink was white, mice that were not accustomed to mirrors before the ink test did not display increased head grooming in any scenario.

“The mice needed significant external sensory cues to pass the mirror test — we have to put a lot of ink on their heads, and then the tactile stimulation coming from the ink somehow enables the animal to detect the ink on their heads via the reflection of the mirror,” says first author John Yukos of University of Texas Southwestern Medical Center. “Chimpanzees and humans don’t need any of this extra sensory stimulation.”

Using gene expression mapping, the researchers identified a subset of neurons in the ventral hippocampus that were activated when the mice “recognized” themselves in the mirror. When the researchers selectively made these neurons non-functional, the mice no longer showed the mirror-and-ink-induced grooming behavior.

A subset of these autoreactive neurons was also activated when the mice observed other mice of the same breed (and thus a similar physical appearance and fur color), but not when they observed a different breed of mice with white fur.

Because previous studies with chimpanzees suggested that social experience was required for self-recognition in the mirror, the researchers also tested mice that had been socially isolated after weaning. These socially isolated mice did not show increased head-grooming behavior during the ink test, nor did black-furred mice raised alongside white-furred mice.

Gene expression analysis also showed that socially isolated mice did not develop autonomic response neural activity in the hippocampus, nor did black-furred mice raised by white-furred mice, suggesting that mice need social experiences alongside other similar experiences. – Researching mice to develop the neural circuits necessary for self-recognition.

“A subset of these self-responsive neurons was also reactivated when we exposed the mice to other individuals of the same strain,” says Kitamura.

“This is consistent with previous human literature that has shown that some hippocampal cells are active not only when a person looks at themselves, but also when they look at familiar people such as a parent.”

Next, the researchers plan to try to separate the importance of visual and tactile stimuli to test whether mice are able to recognize changes in their reflection in the absence of tactile stimuli — perhaps using a technique similar to the filters found in social media apps that allow people to give themselves puppy dog ​​faces or bunny ears.

They also plan to study other brain regions that may be involved in self-recognition and investigate how different regions communicate and integrate information.

“Now that we have this mouse model, we can control or monitor neural activity to comprehensively investigate the neural circuit mechanisms behind how self-recognition-like behavior is induced in mice,” Yukos says.

Financing: This research was supported by the Endowed Scholar Program, the Brain and Behavior Research Foundation, the Daiichi Sankyo Life Sciences Foundation, and the O’Hara Memorial Foundation.

About this neuroscience research news

author: Christopher Benke
source: Cell press
communication: Christopher Benke – Press Cell
picture: Image credited to Neuroscience News

Original search: Open access.
“Visual-tactile integration facilitates mirror-induced self-directed behavior through activation of hippocampal neuronal populations in rats“By Takashi Kitamura et al. nervous cells

a summary

Visual-tactile integration facilitates mirror-induced self-directed behavior through activation of hippocampal neuronal populations in rats

Highlights

• Visual-tactile stimuli facilitate mirror-induced self-directed behavior (MSB) in mice
• Social experience with habituation to the same strain and mirror facilitates MSB
• A subset of ventral hippocampal CA1 (vCA1) neurons responds to self-evoked MSB
• Autoreactive vCA1 neurons respond to the same, but not different, specific strain

summary

Remembering visual features of the self is crucial to self-recognition. However, the neural mechanisms of how visual self-image develops remain unknown due to the limited availability of behavioral models in experimental animals.

Here, we demonstrate mirror-induced self-directed behavior (MSB) in mice, which is similar to visual self-recognition. Mice showed increased marker-directed grooming to remove ink on their heads when an ink-induced visual-tactile stimulus contingency occurred. MSB requires mirror habituation and social experience.

Chemical inhibition of hippocampal dorsal or ventral CA1 (vCA1) neurons attenuated MSB. In particular, a subset of vCA1 neurons that were activated during mirror exposure were significantly reactivated during mirror re-exposure and were essential for MSB.

Self-responsive vCA1 neurons were also reactivated when mice were exposed to a specific type of the same strain.

These results suggest that visual self-image can be developed through social experience and mirror habituation and stored in a subset of vCA1 neurons.