A week ago Stensola et al published evidence that Entorhinal Grid Cells are modular, and on the same day I wrote a glowing commentary, The Significance of the Modular Organization of Grid Cells. In addition to praising the paper, I tried to explain why evidence for modular organization was welcome news, in that it supported computational mechanisms that grid cells could perform. In the rest of this post I outline a model Andre Fenton and I have been working on that relies on discrete modules of grid cells. Our model extracts a function we call linear look-ahead and uses this function for efficient navigation. We feel it represents the begining of a process of explaining high order cognitive functions at the neuron network level Continue reading
Each of us has a semi-coherent theory of the world; I’ll call this a personal belief system. Perhaps this is easy to understand through protypical characters: Religious Joe (RJ) and Secular Mary (SM). Religious Joe’s parents are evangelical, fundamentalist Christians. As a youth he went to Sunday School each week and the majority of his friends and their families shared common beliefs. Joe’s parents taught him “where we came from”, taught him that God was person-like and the bible was literally true. As Joe grew older he began to hear his minister and teachers more frequently.
Enthusiastic and Excited response to the publication of “The entorhinal grid map is discretized” (Stensola, et al, Nature, 492, 72-78; 2012)
The hippocampal formation is an amazing place, populated by strange characters called place cells, head-direction cells and grid cells. Hippocampal place cells exhibit “location-specific firing” (see figure). A single place cell will “fire” only when the rat crosses a restricted region of space. The figure below is an overhead-view map of the firing of a single place cell averaged over a 16-minute recording session (the animal was in a cylindrical enclosure; that’s why the map is round). John O;Keefe, followed by many others, has suggested that the collective firing of hippocampal place cells forms the rat’s “cognitive map”, and permits efficient navigation.
I’d like to start by thanking Gary Marcus for starting a terrific series of Neuroscience discussions from his post as New Yorker’s Neuroscience Blogger. Each topic has been juicy, and each perspective fresh.
This is a continued discussion from Gary’s first post: Moral Machines. As with Gary, I’m going to focus on the design strategy for programming moral behavior into a robot.
Gary’s post focuses on Isaac Asimov’s rules for programming moral behavior into robots. The most prominent commandment is the first:
A robot may not injure a human being or, through inaction, allow a human being to come to harm.
Gary explores whether this is sufficient.
I think Neuroscience has aready had one: Cajal. Read Gordon Shepherd’s 1991 book Foundations of the Neuron Doctrice. The 19th century scientists were lost, arguing about which of the artifacts seen under the microscope were which. Cajal, in remote Spain, peered through his microscope and saw neurons.
Living on the current side of this revolution, its hard to imagine the 19th century image of neural function. Were juices flowing down tubes? Were strings being pulled?
Gary Marcus has a marvelous article in this week’s New Yorker that points out the over-reach the media has imposed on Neuroscience. Neuroscience has progressed, but is still in its infancy. I have no disagreement with Marcus. This post is part of a conversation.
A major culprit has been functional imaging (fMRI) as presented in the media. Functional imaging has been a wonderful advance that permits a glimpse of the activity in regions of the normal human brain. A wonderful tool, but it is a tool with serious limitations. It doesn’t lead to direct understanding how the brain works. Let me explain.