How to Model Neurons (with Jeff Hawkins)

This will be focused on internal engineers, but Jeff is fine with us live-streaming it as well. Today in less than an hour.

12 Likes

Jeff is live now…

4 Likes

Absolutely brilliant video. Thanks Numenta!

15 min 28 seconds into the video Jeff talks about observing the spikes in his jaw muscles.

I had to try this! And indeed I heard it too. It also works when I frown my eyebrows. >:-).

1 Like

Thanks Matt and Numenta. This helps to reinforce my existing knowledge on pyramidal cells within the neo-cortex. As always it also leads to further questions :slight_smile: Such as: Are electro-magnetic effects at play wrt oligodendrocytes myelination of the axon (e.g. frequent axonal spiking attracts/encourages rate of myelination)? Are there inhibitory synapses found everywhere on the axon, or restricted to chandelier neurons affecting the axon hillock? Or wrt to myelin, inhibition that can occur at the nodes of ranvier?

1 Like

Hi Richard,
Myelination makes action potentials travel faster along the axon. I am not aware of any theories that the Myelin sheath plays an information processing role. If you know of any please share. We see Myelin as part of the “plumbing” required to make neurons work and therefore it hasn’t played a part in our theories. I suspect there is a body of literature related to Myelin as it is lost in some diseases.

As far as I know, there are no inhibitory synapses on a axon other than near to the cell body/axon hillock. There is an exception to this. In a few places in the brain there are inhibitory synapses formed on the end of an axon where it forms a synapse. For example, the triadic synapses on thalamic relay neurons, but this is not typical.

5 Likes

An excellent video.

For a newcomer to HTM, what really clarified things for me: Because a set of proximate synapses need to fire on the dendridic tree for a dendridic spike, I am now visualizing the dendridic tree to effectively have branches or sections associated with each of the linked patterns that a given neuron is responding too. The other “aha” moment was the notion that a dendridic spike enables a neuron to fire earlier, and that the inhibitory neuron that fires after the spike is actually shutting the other related neurons down, effectively declaring the fastest spiking neuron the winner.

6 Likes

Do you think inhibit neurons could play a role in eliminating unfitting scenarios in memory selection?
Like the firing stops when the prediction is different from reality :smiley:

The mini-column do what is call bursting and fire even more. This is well described in the Numenta papers; if you are interested in learning more see the BAMI paper here. Search for the keyword burst.

2 Likes

Given the discussion in this video, the concept of bursting described in BAMI (and other Numenta papers) now makes a bit more sense. In those papers, bursting is described as every neuron in the mini-column suddenly firing in response to proximal stimuli for which none of the neurons had recieved a predictive depolarization from the distal dendrites. If none of the neurons fired early (by being in a predictive state), then the inhibitory neurons did not receive an input spike ahead of time, and therefore were unable to inhibit any of the nearby pyramidal neurons. Hence, all of the nearby neurons were allowed to spike in resonse to their proximal inputs.

@Bitking Unless I miss my guess, it’s not that the cells are firing more often, it’s just that there are more cells firing simultaneously.

6 Likes

Yes, a better way to phrase it!

I think I also have a better handle on how the synapse permanences are updated by the neuron activation. Considering that the activated synapses have been recently flooded with ions, they could conceivably be considered to be slightly more conductive than the non-activated synapses. In which case the voltage spike (resulting from the firing of the neuron) travels back down the dendrites preferentially in the direction of the recent ion exchanges. This would sort of be like a static discharge following the path of least resistance to a more neutral state (i.e. whatever passes for ground state). This additional charge/voltage exchange arriving at the recently activated synpases might then allow the synapse to be strengthened through some kind of metabolic response.

The main take-away for me is a better understanding of the biological mechanism for how it is that only the most recently active synapses are reinforced.

5 Likes

I had a twitching muscle in my thumb the other day. I pressed it up to my ear and sure enough, I could hear individual spikes clear as day. Very cool.

2 Likes