The mission of Numenta is to discover the computational principles of the neocortex, the seat of intelligence in our brain. We believe this endeavor requires a detailed understanding of experimental neuroscience, and engaging in discussions with experimental neuroscientists. In October, our VP of Research Subutai Ahmad and I visited two neuroscience institutes on the east coast, the Max Planck Florida Institute of Neuroscience (MPFI) and the Neuroscience Center at the University of North Carolina (UNC). During these trips, we had fruitful discussions with neuroscience research group leaders, postdoctoral researchers and graduate students. We were also pleased that several research groups expressed interest in collaboration. We believe such exchanges with experimental neuroscience groups will help inform and guide future HTM research.
We planned this trip several months ago. It originated due to our previous presentations at academic conferences. Subutai gave a presentation at a workshop at the HHMI Janelia Farm research campus last year, and I gave a presentation at the Dendrite Workshop in Crete, Greece this June. Due to these presentations and our recent publications of HTM theory, researchers at MPFI and UNC became aware of our work at Numenta and invited us to visit their institutes. We believe our efforts to present at academic conferences and publish in scientific journals are highly valuable, as it represents an important step to collaborate with neuroscience researchers.
We hope to do more such trips over the next year, and look forward to increased collaborations with experimental neuroscientists. At Numenta we rely on experimental findings, and it is our hope that new discoveries will continue to inform our ongoing research efforts at Numenta.
For those interested in learning more about the details of our discussions during our trips, I’ve included information below.
Experimental neuroscience, two-photon imaging, and HTM
Traditionally, learning and predicting temporal sequences has not been a focus in studies of sensory cortical areas. However, the ability to recognize and memorize temporal sequences from sensory input streams is critical for almost all cortical functions, from sensory perception to behavior generation, Recent studies suggest that even V1 can learn sequences (Gavornik and Bear, Nature Neuroscience 2016). At MPFI and UNC, Subutai and I presented the HTM sequence memory, a model of how sequence learning could occur in the cortex based on nonlinear active dendrites. The neuroscientists we spoke to are excited about the idea that the primary sensory cortices could also learn sequences, something completely different from what is described in neuroscience textbooks. They like the idea of testing predictions of HTM theory and using HTM as a theoretical framework to design and interpret future experiments.
In the past few years, several major advances in experimental techniques have allowed simultaneous recording of a large neuronal populations in awake, behaving animals. At MPFI and UNC, we witnessed neuroscience experiments with state-of-the-art two-photon calcium imaging techniques. When neurons become active, calcium flows into the cell through ion channels, which causes a transient rise in the calcium level in the postsynaptic cell. Scientists have designed a variety of molecules that respond to the binding of calcium ions by changing their fluorescence properties. Sounds complex, but this just means the neurons emit light when they become active. This revolutionary technique allows scientists to monitor hundreds of neurons, in real-time in living animals, just by using a camera! Here is a video of calcium imaging from mouse V1 during presentations of drifting grating stimuli.
In a recent study published in Nature Neuroscience, PhD student Dan Wilson and Postdoc David Whitney from Prof. Fitzpatrick’s lab at MPFI assessed the orientation tuning of individual dendritic spines and evaluated how the nonlinear dendritic property shapes the computation of cortical pyramidal neurons. Non-linear dendrites are a key component of HTM theory and we were impressed by this ability to record live from populations of dendritic spines of single neurons (spines are essentially synapses). Prof. Spencer Smith at UNC has published several important papers on active dendrites. In his lab, researchers are now developing next generation 2-photon imaging systems, which enable simultaneously recording neuronal activities from multiple brain areas with expanded fields of view. This technique was published in Nature Biotechnology earlier this year.
HTM theory is constrained by neuroscience evidence, and as such these experimental techniques can be useful tools to test predictions of the theory. We have described a set of testable experimental predictions in a paper published in Frontiers in Neural Circuits. For example, HTM theory predicts that each sensory input activates a sparse set of cells that are specific to the context of a sequence. These cells will then trigger active dendritic spikes and depolarize another set of cells that correspond to the upcoming inputs. In the future we hope it will be possible to directly test the presence of such “cell assemblies” with two-photon imaging or other techniques.
Yuwei Cui • Research Engineer