How Big is Mouse Brain?

This article will cover information on how big the mouse brain is. It will also cover information on the functions of the mouse brain. The article will highlight the similarities and differences between the human and mouse brain. 

How Big is Mouse Brain?

The mouse brain is the size of a pea, roughly. It comprises roughly eight to fourteen million neuronal cells and glial cells. Scientists have put in effort since 2006 to create an atlas of the mouse brain in a 3D model. This has been made possible with the help of newer advances in imaging, sequencing, as well as computerised technology (Dong, 2008).

The mouse brain is not a mini replica of the human brain. However it has been a powerful model in assisting neuroscientists to study the human brain and its functions as well as disorders of the brain. This is because the genes that build and operate both humans and the rodent species are about 90% identical (Chon et al., 2019). 

As compared to the mouse brain, the human brain contains more than 100 billion neurons. These neurons are connected with other neurons with the help of synapses. This makes the human brain a 3-pound, or 1.4 kg organ in the brain which is more complex than the numerous individual parts that make up the brain. 

Because of the advancements in the science field under techniques of imaging, sequencing, and computerised technologies, scientists aim to map the human brain at the highest resolution along with all of the molecular as well as cellular components of the brain. While we are yet to achieve this, we have created an atlas of the mouse brain. 

Comparisons of the human and the mouse brain

One difference between the human and the mouse brain is in size and weight. The human brain is bigger and denser than the mouse brain. The cerebral cortex of the mouse brain has over 8 to 14 million neurons. The human cerebral cortex has more than 10 to 15 billion neurons (Strand et al., 2007). 

Another difference is that the olfactory bulb of the mouse brain takes up 2% of space in the brain, while the volume of the olfactory bulb is around 0.01% in the human brain. 

These differences raise questions about the quality of comparisons made between the mouse and the human brain. For instance, scientists are increasingly gaining popularity in genetic studies but the mouse brain only weighs only about a few grams whereas the human brain weighs 1.4 kilograms. Hence, is it really justified for us to use the mouse brain to learn about ours (Strand et al., 2007).

In the area of brain research, there is an accepted assumption that the core areas of the brain have originated together through the course of evolution, and hence our brains are similar to mice brains. 

However, in recent times, emerging research has shown that 80% of the human subcortical striatum has not been found in the mouse brain. These areas are important in humans for the processing of language and social cognition. Even the areas that are similar in mice and humans in regard to the brain, human brains have more complex connections in those areas (Song et al., 2020).

The entire mouse brain has approximately 31 terabytes of imaging data. This equals 32 million digital photographs. Amongst the similarities between the human and the mouse brain, there are several differences between the same. The most important difference has been found in the activity of genes responsible for the functions of the neurotransmitter serotonin. 

The cells that sense serotonin in mice are different from those cells that sense serotonin in humans. Thus, laboratory studies on mice that involve serotonin-induced disorders such as depression are not good enough for comparisons in humans. 

Another striking difference lies in microglia, where immune cells of the brain reside. Microglia have different gene behaviours in humans and mice. For instance, in humans, microglia are suspected for involvement in diseases like Alzheimer’s disease and Parkinson’s disease (Leung & Jia, 2016). 

Human brains are approximately 15 times larger than the mouse’s brain. Humans, even keeping aside bodily size differences, humans have larger brains. However, there is no relationship between brain size and intelligence when it comes to humans. Since the Neanderthal brain is considered to be just as big, or even bigger as compared to the homo sapien brain. 

Another difference between Mouse and Human Brain is that the human brain has the component of neuroplasticity, where the human brain is influenced by environmental or genetic factors throughout the lifespan. 

Another difference is that the human brain grows rapidly during the first year of life. The human brain also has the ability to develop sophisticated linguistic skills, in which we can communicate information with others in a rapid and efficient manner. Humans also have the ability to coordinate and plan actions, as well as engage in complex decision-making. 

Memory is another distinct feature of the human brain. In which, humans tend to remember words and what they mean. Humans also have a vocalisation system which helps us in speaking what we want, and coordinate our muscles so that we can make the correct noises. 

Interesting Facts about the Human Brain

Below are some interesting facts about the human brain:

  • 60% of the brain is actually made of fat. This makes the brain the fattiest organ in the human body. These fatty acids are important for the efficient performance of the brain. Hence, it is necessary to fuel the brain with healthy nutrients.
  • The brain is not fully formed until the age of 25. Brain development starts from the back of the brain and then progresses to the front. Thus, the frontal lobes are the last to strengthen and make structural connections. The frontal lobes are responsible for planning and reasoning.
  • The brain’s memory storage capacity is assumed to be virtually unlimited. The brain contains about 86 billion neurons, which form connections with each other. This adds up to one quadrillion connections or 1,000 trillion connections. These neurons, over time, combine and further increase the storage capacity.
  • It is important to note that in Alzheimer’s disease, a lot of neurons can get damaged and stop working, resulting in affecting the memory.
  • Brain information can travel up to 268 miles per hour. Neurons, when stimulated, generate electrical impulses which can travel from cell to cell and transmit information. When this process is disrupted, it can cause seizures or epilepsy.
  • By the age of 4, the spinal cord stops growing. The spinal cord is a bundle of nerve tissues that support cells. It is responsible for transmitting messages from the brain to the body, and vice versa. The spinal cord is considered to be the main source of communication that connects the body to the brain. In cases where the spinal cord is affected, this communication is ruptured and can affect the immune system of the individual suffering from it.
  • It is not true that we only use 10% of our brain. In fact, we use all of it, even while sleeping. Neuroscientists have now confirmed that the human brain is always active.


The article covered details about how big the mouse brain is. The article also highlighted the similarities and differences between the human and mouse brain.

Frequently Asked Questions: How Big is Mouse Brain?

Which animal has 32 brains?

Leech has 32 brains. The leech’s internal structure is divided in 32 separate segments and each segment has a brain of its own. Leech is known to be an annelid. 

Are mice smart?

Rodents are considered to be highly intelligent rodents. They are excellent when it comes to learning and understanding concepts. Though rats are smaller than dogs, they have similar abilities like dogs when it comes to thinking and figuring things out.

How many cells are there in a mouse brain?

The total number of neurons in the entire mouse brain is considered to be around 70 million (Herculano-Houzel et al., 2006).


Chon, U., Vanselow, D. J., Cheng, K. C., & Kim, Y. (2019). Enhanced and unified anatomical labeling for a common mouse brain atlas. Nature communications, 10(1), 1-12.

Dong, H. W. (2008). The Allen reference atlas: A digital color brain atlas of the C57Bl/6J male mouse. John Wiley & Sons Inc.

Leung, C., & Jia, Z. (2016). Mouse genetic models of human brain disorders. Frontiers in genetics, 7, 40.

R.D. Hodge et al. Conserved cell types with divergent features in human versus mouse cortex. Nature. Published online August 21, 2019. doi:10.1038/s41586-019-1506-7.

Song, H. W., Foreman, K. L., Gastfriend, B. D., Kuo, J. S., Palecek, S. P., & Shusta, E. V. (2020). Transcriptomic comparison of human and mouse brain microvessels. Scientific reports, 10(1), 1-14.

Strand, A. D., Aragaki, A. K., Baquet, Z. C., Hodges, A., Cunningham, P., Holmans, P., … & Olson, J. M. (2007). Conservation of regional gene expression in mouse and human brain. PLoS genetics, 3(4), e59.