(Updated with comparison to Mankin et al Feb 20; in red text)
“Long-term dynamics of CA1 Hippocampal Place Codes” is an important study published in the current issue of Nature Neuroscience. The paper is noteworthy in terms of technical achievement, theoretical implications and the potential for future work
Headstage on mouse brain. Ziv et al fig 1a.
First, the technical achievement. Ziv et al, working in Mark Schnitzer’s group at Stanford have managed to record the firing activity of hundreds of hippocampal neurons over a period of approximately one month. They do this by permanently mounting a miniature camera on the mouse’s head and using Ca+ imaging to identify the firing pattern of each neuron. Continue reading
The term “egocentric” has nothing to do with Freud or selfishness. It’s a geometric term meaning that part of the self is the center of the spatial coordinate frame (“ego” = self). The contrasting term, “allocentric” means something other than the self is the center of the coordinate frame (“allo”= other). A comparison has helped me: think of geocentric and heliocentric models of the solar system.
The question I’m going to address is whether our brains, our perception of the world, our behavior, and our consciousness operate in egocentric or allocentric coordinate frames.
List 1: “essential consciousness (level 1)”. I suggest these are the core features of consciousness, common to all conscious creatures on planet earth.
List 2 : “Level 2 consciousness”. Level 2 consciousness is a higher consciousness, present in most humans and, likely some other mammals. Level 2 is qualitatively different from level 1 and some consider it to be true “conscious”. I’ve taken the approach of distinguishing two levels. My dogs are conscious, but not level 2.
List 3: “Biological Features Connected to Consciousness” A speculative list of behavioral and structural features whose evolution may be tied to consciousness.
(the following is a short piece I wrote two years ago in a private blog. I’m making it public and reposting because of similarities to arguments in John Searle’s review of Chistof Koch’s book in the NYRB. I found Searle’s review excellent. Unfortunately, most is behind NYRB firewall)
David Chalmers proposes that consciousness is inherent in informational structures1,2. As a reductionist example, he suggests that a computer, which organizes large quantities of information, or a thermostat, which organizes much smaller quantities, has a measure of consciousness. Some physicists (Penrose, Wheeler) have proposed that when natural phenomena are better understood, ‘information’ (non-random organization) will be recognized as a principal feature. Continue reading
David Marr was a brilliant Neuroscientist who died too young, in 1980, at the age of 35. Marr’s work was theoretical — he was at the leading edge of a computational wave.* Marr’s contributions spanned many areas of Neuroscience: cerebellum, hippocampus, and especially vision. Marr is also well known for proposing that brain/behavior function should be approached in three phases that are largely sequential:
- The computational level: what is the problem that confronts the animal?
- The algorithmic level: How is it logically solved? (including shortcuts)
- The implementation level: How does the brain do it?
A year ago Dayu Lin and co-authors published a landmark study in Nature on the hypothalamic nucleus which, when optically stimulated, produces undifferentiated rage. At that time Ed Yong wrote a wonderful summary of the work.
The point: in the mouse there is a region in the hypothalamus which, when stimulated, produces undifferentiated rage. There is reason to believe there is an equivalent region in humans. While we don’t go around with optogenetic probes in our brains, the state of undifferentiated rage is not uncommon. Many of us have experienced times when rage is out of control — difficult to keep in check by reason or logic. This is why I don’t like having guns within easy reach.
A fanciful depiction of how a grid cell based navigation system could compute a direct path across unvisited regions of space.
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