This project is a simple Python implementation of Numenta's HTM algorithm along with visualization software using OpenGL. The purpose of this project is to achieve a foundational understanding of cortical neuroscience principles and demonstrate these intelligence principles by implementing HTM algorithms.
Please note, this code is out dated. For an up to date version go to the htm-opencl repository.
The human cortex is about 2-3mm thick with many regions arranged in a hierarchy. Some basic regions include:
- Frontal Lobe:
- Parietal Lobe:
- Occipical Lobe: vision
- Temporal Lobe:
Each region of the cortex typically contains 6 layers (5 layers of neurons and an axon layer).
- Pial Surface
- Layer 1:
- Layer 2:
- Layer 3: One of the primary feedforward layers. Multiple cells per column useful for inference and prediction of moving images (Numenta).
- Layer 4: One of the primary feedforward layers. One cell per column useful in forming representations that are invariant to spatial changes (Numenta).
- Layer 5: Motor behavior
- Layer 6: Feedback
- White Matter
Each layer contains ocolumns of neurons that all respond to a particular stimulus.
Mini-columns are vertical structures through the 6 layers of cortex comprising of about 80-120 neurons. A neuron's feed forward input, the proximal dendrite, attaches to a receptive field, or particular area of sensory space in which stimulus will trigger the firing of the neuron. Neurons in a minicolumn have the same receptive field. Therefore in the HTM algorithm for organizational purposes, each column stores proximal dendrites rather than each neuron in a column.
The structure of an HTM cell, or neuron, is modeled after pyramidal neurons in the neocortex. In a real neuron when it is in an active state the axon outputs a short burst of action potentials. When it is in a predictive state the axon outputs a slower, steady rate of action potentials. These action potentials are only modeled with a binary "on" or "off" for a cell's state.
- Proximal Dendrite Segment: recieve feedforward input and used to put a neuron in an active state.
- Apical Dendrite Segments: recieve feedback from higher cortical layers and used to put a neuron in a predictive state.
- Basal Dendrite Segments: recieve lateral input from nearby neurons and is used to put a neuron in a predictive state.
- Potential Synapses: Represents all the axons that pass close enough to a dendrite segment that they could potentially form a synapse.
- Permanance: A scalar value representing the range of connectedness between an axon and a dendrite. If the permanance is above a certain threshold, the synapse is connected.
The spatial pooling function operates on a layer of a cortical region. It uses each column's proximal dendrite input to return active columns that reflect the greatest connectivity with that layer's input.
- Potential Pool: Each column sees a random subset of the input bits.
- Overlap Score: How many of column's connected synapses(permanance above threshold) are binary 1.
- Inhibition: enforce sparcity by selecting active columns from the top overlap scores.
- Learning: Look at all the active columns and strengthen or weaken connections.
- Output: active columns
The temporal memory function operates at the neuronal level by by using each neuron's basal dendrite input. Apical dendrites have not been implemented in this version of the algorithm.