# What's the difference between layers and levels in the context of the HTM theory? **URL:** \ **Category:** Numenta Theory\ **Tags:** question\ **Created:** [August 13, 2018, 12:37am UTC](https://discourse.numenta.org/t/whats-the-difference-between-layers-and-levels-in-the-context-of-the-htm-theory/4335 "2018-08-13T00:37:31Z")\ **Posts on this page:** 1\ **Showing post:** 2

**Author:** ![Bitking](https://yyz2.discourse-cdn.com/flex030/user_avatar/discourse.numenta.org/bitking/32/3099_2.png) [@Bitking](https://discourse.numenta.org/u/Bitking)\ **Post date:** [August 13, 2018, 5:12am UTC](https://discourse.numenta.org/t/whats-the-difference-between-layers-and-levels-in-the-context-of-the-htm-theory/4335/2 "2018-08-13T05:12:12Z")

I will be the first to agree that naming in neuroscience could be better. As I understand it, the sheet of the cortex is composed of what is generally recognized as six layers. The outer layer (one furthest from the center of the brain) is called layer one The bottom is generally called layer six. These are not hard and fast divisions as the whole concept of what makes up a layer is pretty loose at this time. There are some that consider the thalamus as the 7th layer. This same sheet of the cortex has subtle variations that are discernable with different methods. Two of the oldest are inspection with low power magnification, or by noting what defects occur if some area is damaged - say by a war wound. These older techniques have settled on the map offered by Brodmann: > **[Brodmann area](https://en.wikipedia.org/wiki/Brodmann_area)** > > A Brodmann area is a region of the cerebral cortex, in the human or other primate brain, defined by its cytoarchitecture, or histological structure and organization of cells. > Brodmann areas were originally defined and numbered by the German anatomist Korbinian Brodmann based on the cytoarchitectural organization of neurons he observed in the cerebral cortex using the Nissl method of cell staining. Brodmann published his maps of cortical areas in humans, monkeys, and other species in 1909, along ... these can be called maps, areas, or regions - all mean the same thing. One of the newer techniques is to look with various 3D imaging methods and follow the connecting tracts - what is hooked to what. > **[Connectome](https://en.wikipedia.org/wiki/Connectome)** > > A connectome (/kəˈnɛktoʊm/) is a comprehensive map of neural connections in the brain, and may be thought of as its "wiring diagram". More broadly, a connectome would include the mapping of all neural connections within an organism's nervous system. > The production and study of connectomes, known as connectomics, may range in scale from a detailed map of the full set of neurons and synapses within part or all of the nervous system of an organism to a macro scale description of the functional and... This method has roughly doubled the number of identified maps/areas/regions. The tool that has come out of this effort is the connectogram, see this list of maps at the bottom of this link: > **[Connectogram](https://en.wikipedia.org/wiki/Connectogram)** > > Connectograms are graphical representations of connectomics, the field of study dedicated to mapping and interpreting all of the white matter fiber connections in the human brain. These circular graphs based on diffusion MRI data utilize graph theory to demonstrate the white matter connections and cortical characteristics for single structures, single subjects, or populations. > The connectogram, as a graphical representation of brain connectomics, was proposed in 2012. > Circular representations o... It has been observed that in these map-to-map connections there are definite pathways. In these streams, there is a general scheme of progressing from the senses to the association region. Each of the sensory modalities seems to have this processing stream and this progression from senses to the association region is generally referred to as a hierarchy. There are similar streams in other places in the brain but that is more complicated than I want to tackle in an introductory post. > **[Visual cortex](https://en.wikipedia.org/wiki/Visual_cortex)** > > The visual cortex of the brain is that part of the cerebral cortex which processes visual information. It is located in the occipital lobe. Visual nerves run straight from the eye to the primary visual cortex to the Visual Association cortex. > Visual information coming from the eye goes through the lateral geniculate nucleus in the thalamus and then reaches the visual cortex. The part of the visual cortex that receives the sensory inputs from the thalamus is the primary visual cortex, also known ... > **[Auditory cortex](https://en.wikipedia.org/wiki/Auditory_cortex)** > > The auditory cortex is the part of the temporal lobe that processes auditory information in humans and other vertebrates. It is a part of the auditory system, performing basic and higher functions in hearing, such as possible relations to language switching. > It is located bilaterally, roughly at the upper sides of the temporal lobes – in humans on the superior temporal plane, within the lateral fissure and comprising parts of Heschl's gyrus and the superior temporal gyrus, including planum polar... I want to add that these graphs that show a general stream make it look simple. This can be deceiving as in reality, the brain is very complex with a bewildering collection of skips and side connections in these streams. This paper should give a more realistic view of what a neuro-scientist is up against - see figure 1: > **[Subdivisions of auditory cortex and processing streams in primates](https://www.pnas.org/content/97/22/11793)** > > The auditory system of monkeys includes a large number of interconnected subcortical nuclei and cortical areas. At subcortical levels, the structural components of the auditory system of monkeys resemble those of nonprimates, but the organization at... **But wait - there’s more!** The progression of processing the main sensory streams seems to be split into two major paths - one is called the WHAT stream, and one is called the WHERE stream. > **[Two-streams hypothesis](https://en.wikipedia.org/wiki/Two-streams_hypothesis)** > > The two-streams hypothesis is a model of the neural processing of vision as well as hearing. The hypothesis, given its initial characterisation in a paper by David Milner and Melvyn A. Goodale in 1992, argues that humans possess two distinct visual systems. Recently there seems to be evidence of two distinct auditory systems as well. As visual information exits the occipital lobe, and as sound leaves the phonological network, it follows two main pathways, or "streams". The ventral stream (a Sever... “WHAT and WHERE pathways” [http://www.scholarpedia.org/article/What\_and\_where\_pathways](http://www.scholarpedia.org/article/What_and_where_pathways) **Do you want to dig deeper?** Here is some associated reading that should show these streams in action and give you a flavor for what is going on. You can skip these without guilt as they are more in-depth than most newbies are ready to digest. > **[Ventral and dorsal pathways for language](https://www.pnas.org/content/105/46/18035)** > > Built on an analogy between the visual and auditory systems, the following dual stream model for language processing was suggested recently: a dorsal stream is involved in mapping sound to articulation, and a ventral stream in mapping sound to... > **[What Visual Information Is Processed in the Human Dorsal Stream?](http://www.jneurosci.org/content/32/24/8107)** > > The idea of a division between a dorsal and a ventral visual stream is one of the most basic principles of visual processing in the brain (\[Milner and Goodale, 1995\]\[1\]). The ventral stream originates in primary visual cortex and extends along the... > **[Hierarchical processing for speech in human auditory cortex and beyond](https://www.frontiersin.org/articles/10.3389/fnhum.2010.00051/full)** > > A commentary onHierarchical organization of human auditory cortex: evidence from acoustic invariance in the response to intelligible speech.by Okada, K., Rong, F., Venezia, J., Matchin, W., Hsieh, I.-H., Saberi, K., Serences, J. T., and Hickok, G.... > **[Principles of Temporal Processing Across the Cortical Hierarchy](https://www.sciencedirect.com/science/article/pii/S0306452218302951)** > > The world is richly structured on multiple spatiotemporal scales. In order to represent spatial structure, many machine-learning models repeat a set o… I hope this helps. --- _[View the full topic](https://discourse.numenta.org/t/whats-the-difference-between-layers-and-levels-in-the-context-of-the-htm-theory/4335)._