An Introduction to Cortical Modularity

Many years ago, Lorente de No, a student of Cajal, described the presence of a repeating circuit within the cerebral cortex.  He said that, respective of anatomical location, all information going to the cortex was processed through a similar arrangement of cells.  A couple of decades later the eminent neuroscientist Vernon Mountcastle provided electrophysiological evidence for such a circuit.  After impaling over 10,000 neurons Mountcastle noted the existence of radially arranged cells (like pearls on a string) throughout the neocortex.  These strings had the following properties: a) they collected information from the same place (terminal fields) and, b) their constitutive cellular elements reacted together when any one of them was stimulated.  Since these properties persisted only for neurons within small columnar arrangements, Mountcastle called them mini- or microcolumns.

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Lorente de No

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Vernon B. Mountcastle

In-keeping with systems theory, minicolumns are said to provide the smallest modular element of information processing within the cerebral cortex. This is a striking tenet as some neuroscientists would argue in favor of the neuron as the basic unit of information within the brain.  However, neurons do not process information in isolation and, if cultured, can only survive and differentiate if grouped together.  Genetically designed animals where communication between neurons is prevented leads to major neuronal loss and is incompatible with life.

Groups of minicolumns, macrocolumns and networks of macrocolumns provide for different levels of hierarchical organization within the cerebral cortex.  In essence, by adding neurons together into circuits the brain has been able to generate “unexpected” properties that were not present in the individual elements.  A suitable analogy is that of a car wherein by putting together different modules such as a steering wheel, motor, transmission, etc. we obtain locomotion.  In the case of minicolumns, spectacular work by Ioan Opris has shown that minicolumns within the frontal lobes of nonhuman primates provide for the emergence of executive functions.  The latter is an umbrella term for cognitive processes such as working memory, attention, mental flexibility, etc.  In a conference that I attended many years ago, the late Patrica Goldman-Rakic aptly described the executive functions as a from of “clipboard memory”.

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A cross section of the cerebral cortex showing the columnar orientation of neurons.

More recent work, again by Ioan Opris and colleagues, has shown that the circuitry of the minicolumn can be used to restore function in an area of the brain that has been blocked or ablated by pharmacological means.  The finding provides hope of using minicolumnar circuitry as a prosthetic agent in the treatment of degenerative (e.g., Alzheimer’s disease) and vascular conditions (e.g., stroke) affecting the cerebral cortex.

Otto Detlev Creutzeldt, a contemporary to Mountcastle, was probably the first to propose that the minicolumn was akin to an electrical wall socket.  Creutzfeldt wrote a classic textbook, translated into English and published by Oxford University Press, about the organization of the cerebral cortex: “Cortex Cerebri”.  According to Creutzfeldt, minicolumns were agents capable of running information transmitted from different sources.  The output was thus dependent on the source of information. Although other scientists initially negated the concept, the role of minicolumns has been revisited due to multiple experiments having to do with brain plasticity.

For those interested in further reading on the subject of neuroplasticity there are a number of excellent books for the layman.  I recommend the following ones:

1)   The Mind and the Brain by Jeffrey Schwartz and Sharon Begley

2)   Train Your Mind Change Your Brain by Sharon Begley

3)   The Brain that Changes Itself by Norman Doidge

4)   A personal take on neuroplasticity by the neuronatomist Jill Bolte Taylor in “My Stroke of Insight”

As an example of neuroplasticity or the electrical wall socket idea of Creutfeldt, the late polymath Paul Bach-y-Rita provided a series of studies that introduced the phenomenon of “sensory substitution” to the field of neuroscience.  In essence, if you damage a part of your brain mediating one of our senses, other parts can sometimes take over the process.

Classical neuropathologists are neuronal chauvinism.  They believe, just as Ptolomei, that neurons stand at the center of their diagnostic universe. Conditions are called pathological only when neurons or glia disappear, are shrunken, or stain differently.  This is a reductionists’ approach to science. What happens when the  pathology escapes this level of resolution?  What happens when abnormalities are present at the level of circuitry and not at the level of single cells? For mental disorders affecting higher cognitive functions the localization of pathology should involve those anatomical structures that give rise to the same. In this regard we should look for pathology in conditions such as autism, schizophrenia and bipolar disorders in the modular organization of the cortex.

Additional references:

1) Casanova MF, Tillquist C. Encephalization, emergent properties, and psychiatry: a minicolumnar perspective.  The Neuroscientist, 14:101-118, 2008.

2) Casanova MF. Cortical organization: a description and interpretation of anatomical findings based on systems theory.  Translational Neuroscience, 1(1): 62-71, 2010.

3) Casanova MF, El-Baz A, Switala A. Laws of conservation as related to brain growth, aging, and evolution: symmetry of the minicolumn. Frontiers in Neuroanatomy, 5:66, 2011.

5 responses to “An Introduction to Cortical Modularity

  1. Don’t forget glial cells. I don’t know if they exist on a minicolumnar arrangement, but apparently their importance has been underestimated until recent years. R. Douglas Fields discusses this in the book “the other brain”

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  2. I read the book sometime ago. I may disagree with the author as to the origins of microglia. The overall concept of both microglia and astrocytes as providing nets via gap junctions and scanning their environment in short periods of time has only been around for a decade or so.
    Some astrocytes have a so-called velate appearance that keep a radial orientation within the gray matter of the cortex and cerebellum. In this regard they may form a component of the cell minicolumn.
    I will have to write a future blog about neuroinflammation and autism explaining the role of these cells.
    Thank you for the comment.

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  3. Pingback: The Cerebral Cortex and Autism | Cortical Chauvinism·

  4. Pingback: Características neuroanatómicas y neuropatológicas del autismo | Cortical Chauvinism·

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