As I begin this series of blogs some definitions are in order. I will be focusing on a specific part of pyramidal neurons, the dendrites and their apical tufts. The information I am sharing is extracted from two articles, the first: M. W. Spratling, “Cortical Region Interactions and the Role of Apical Dendrites,” Behavioral and Cognitive Neuroscience Reviews, 1(3): 219-228, 2002, and the second: Nelson Spruston, “Pyramical Neurons: Dendritic Structure and Synaptic Integration,” Nature Reviews: Neuroscience, Vol. 9, March 2008, 206-221.
The cerebral cortex consists of a laminar structure of six layers. The cell bodies of pyramidal cells, the most abundant type of cortical neuron, are found in layers II-VI and have distinct morphologies, including two separate dendritic arbors: the basal dendrites which occupy the same layer as the cell body and the apical dendrites which ascend into more superficial layers. For pyramidal cells in layer VI the apical dendrites extend to layer IV, and for pyramidal cells in the other layers the apical dendrites extend to layer I where they are quite dense. Pyramidal cells consist of the only neurons that project outside the cortex “and [are] the primary source of connections between different cortical areas. This class of cell is thus likely to have a major role in cortical information processing.” (I remind the reader that information can only be generated by a mind, discussed in detail in previous blogs and in my books.)
Both the apical and basal dendrites receive connections with axons originating in different cortical areas. They are rich in dendritic spines that project from the dendritic body and along its length to make connections with boutons, specialized pre-synaptic structures at the ends of axons. Between the bouton and the spine is a very narrow synaptic cleft across which neural transmitters flow to generate action potentials transmitted through synaptic networks. Spines are highly variable in their size and shape and are plastic, changing with experience. “It has been suggested that thin, dynamic spines might be available to contribute to learning, whereas larger, more stable spines might be involved in the storage of established memories. Repeated activation of small spines leads to increase in their size by the Hebbian process discussed in my books.
Spruston describes pyramidal neurons as having basal and apical dendrites along with apical tufts. In my research I wonder if the wave forms that appear to be generated by cognition of the immaterial mind interact with the spines of apical dendrites within the apical tufts? Does this interaction occur at ionic channels in the tufts and/or in the specialized, pre-synaptic structures? Are axons involved? What is the result of the proposed interaction, and how are spike trains of action potentials generated that are transmitted through synaptic channels to bring about intended action? As this discussion proceeds I shall address these questions in relation to my postulate that apical tufts are sites for interaction with the immaterial mind.
My discussion that follows will focus on the basics of apical dendritic function which is markedly complex. The two articles to which I am making reference discuss this function in more detail. My focus is to address only one aspect of its function in relation to cognitive activity within the cerebral cortex, giving expression to related points made in earlier blogs in this context. Each blog that follows in this series will be entitled, “Apical tufts in cognition, part 1, 2, etc.” I invite the reader to brainstorm along with me as I make the case for dualist interaction!