A cubic millimeter of brain tissue ...

by pepgma 22.3.15 0 comments neuroscience science

Some facts about brain density:

• The size of a bee's  brain is around 1 cubic millimeter and contains around 1 million neurons (C. B. Don). This is enough to perform all basic movement activities, communication, and even a social life. The human brain is around 1.2x10⁶ cubic millimeters.
• “One cubic millimeter of cerebral cortex contains roughly 50,000 neurons, each of which establishes approximately 6,000 synapses with neighboring cells (Beaulieu and Colonnier, 1983). These 300,000,000 interconnections are highly specific: neurons innervate some target cells but avoid others. Of course, a cubic millimeter is but a miniscule part of the full circuitry, which is estimated to contain 60x10¹²” (CRL Harvard).
• “One cubic millimeter is 1/1000 of a cubic centimeter and 1/1000000 (10^-6) of the entire volume of the brain. We can scale the total number of connections in the brain (using the high estimate of 10¹⁵ connections in the brain) then we find that there are 10⁹ connections in a cubic millimeter of the brain.” The Astronomist
• Another estimate of connectivity density: “In every cubic millimeter of cortical tissue about a million of neurons must be wired appropriately for their respective functions such as the analysis of sensory inputs, the storage of skills and memory, or for motor control.” Max-Planck-Institute for Dynamics and Self-Organization
• One cubic millimeter of cortical tissue amounts to 4 km of axon cables, 500 m of dendrites and around one billion synapses (Braitenberg and Schüz, 1998).
• “Imaging a cubic millimeter of brain tissue requires one petabyte of storage space (10⁶ gigabytes = 1000 terabytes = 1 petabyte)!  With the current technology, it would take about 10 million years to map every synapse in a human brain, and would require several million more petabytes of data to store the information.” Knowing Neurons

Image: Hippocampus Brainbow by Dr. Tamily Weissman

Note: This post is an update from an older post in September 2007, created after a quote from the Max-Planck-Institute for Dynamics and Self-Organization in Germany. In 2008 I joined this institute to write my doctoral dissertation.