Regions

The notion of regions wired in a hierarchy comes from biology. The neocortex is a large sheet of neural tissue about 2mm thick. Biologists divide the neocortex into different areas or “regions” primarily based on how the regions connect to each other. Some regions receive input directly from the senses and other regions

receive input only after it has passed through several other regions. It is the region- to-region connectivity that defines the hierarchy.

All neocortical regions look similar in their details. They vary in size and where they are in the hierarchy, but otherwise they are similar. If you take a slice across the

2mm thickness of a neocortical region, you will see six layers, five layers of cells and

one non-cellular layer (there are a few exceptions but this is the general rule). Each layer in a neocortical region has many interconnected cells arranged in columns. HTM regions also are comprised of a sheet of highly interconnected cells arranged in columns. “Layer 3” in neocortex is one of the primary feed-forward layers of neurons. The cells in an HTM region are roughly equivalent to the neurons in layer

3 in a region of the neocortex.

Figure 1.3: A section of an HTM region. HTM regions are comprised of many cells. The cells are organized in a two dimensional array of columns. This figure shows a small section of an HTM region with four cells per column. Each column connects to a subset of the input and each cell connects to other cells in the region (connections not shown). Note that this HTM region, including its columnar structure, is equivalent to one layer of neurons in a neocortical region.

Although an HTM region is equivalent to only a portion of a neocortical region, it can do inference and prediction on complex data streams and therefore can be useful in many problems.