Figure 1.
Effect of training on orientation discrimination in V1 neurons.
A. Orientation discrimination task. Subjects reported whether the test orientation was tilted clockwise or anticlockwise with respect to the trained orientation (from [7]). B. Performance in orientation discrimination task (from [7]). C. Orientation tuning curves of five sample V1 neurons (from [7]). D. Slope measured at the trained orientation for trained neurons (solid red line) and naïve neurons (dashed blue line) (from [7]). E. Performance in orientation discrimination task in another experiment (from [8]). F. Neural responses in V1 in the trained location (grey line) and an untrained location (black) (from [8]).
Figure 2.
Layer one represented layer 2/3 of V1 and contained excitatory and inhibitory neurons. Layer two represented V2 area and contained excitatory neurons. V1 neurons were connected through recurrent (excitatory and inhibitory) connections. V1 neurons received bell-shaped input, which mimicked orientation-tuned input from layer 4 neurons of V1. V1 excitatory neurons sent convergent feedforward projections to excitatory V2 neurons. V2 neurons projected back to all V1 neurons. Stimuli of different orientations were modeled by shifting the center of the input along one-dimensional network.
Figure 3.
A. With learning, feedforward connections from a population of V1 neurons to a population V2 neurons strengthened. B. The excitatory V2 neurons projected to both the excitatory and inhibitory neurons in V1. C. Top. Membrane potential of a V1 neuron before training. Bottom. Excitatory and inhibitory input currents to the V1 neuron before training. D. Top. Membrane potential of the V1 neuron after training. Bottom. Excitatory and inhibitory currents to the V1 neuron after training. E. Response function (f-I curve) of a V1 neuron. The neuron did not respond to the trained stimulus, and the response function was tested by injecting current to the neuron.
Figure 4.
Enhancement of stimulus selectivity.
A. Tuning curve of a V1 neuron that preferred the trained orientation; before (black) and after (green) training. B. Amplitude-to-width ratio (R) of the tuning curve before (black) and after training (green) in a neuron that preferred the trained orientation, and in a neuron that preferred different orientation (blue). C. Tuning curve of a V1 neuron that preferred orientation different than the trained one; before (black) and after (blue) training. D. Slope change of the tuning curve of the V1 neuron the preferred the trained orientation (green) and another V1 neuron that preferred another orientation (blue line with filled circles).
Figure 5.
Stimulus specificity of tuning curve changes.
A. Training the model with stimulus A strengthened the feedforward and feedback connections between stimulus-specific populations of V1 and V2 neurons. B. A test stimulus B (green) activated population of neurons in V1 and V2 that included some neurons with the modified synapses. The red circle shows where the trained stimulus A was presented to the model. C. Another test stimulus C (purple) activated populations of V1 and V2 neurons that did not include neurons with modified synapses. D. Before training, the strength of the feedback inputs was equal for any applied stimulus (grey dashed line). After training, the strength of feedback inputs depended on the applied stimulus (black solid line). E. Stimulus specificity of changes to tuning curves. Peaks of tuning curves did not change, but amplitudes and widths of the tuning curves changed depending on the distance from the trained orientation.
Figure 6.
Effect of feedbacks on population response in V1.
A. Population response in V1 to a stimulus before training, with (black) and without (grey) recurrent connections among V1 neurons. B. Input-output function in V1 neurons, with (black) and without (grey) recurrent connections among V1 neurons. C. Population response in V1 to the trained stimulus (preferred stimulus for neuron A) before and after training. D. Responses of neurons A and B to the trained stimulus (preferred for neuron A) changed due to feedback. Black line indicates input-output relation in V1. Blue arrows indicate the strength of feedback inputs. Black and grey filled circles represent neural response of neurons A and B to the trained stimulus before and after training. E. Population response in V1 to a novel stimulus (preferred for neuron B), before and after training with the stimulus preferred for neuron A. F. Responses of neurons A and B to the novel stimulus (preferred for neuron B) changed due to feedback. Black line indicates input-output relation in V1. Blue arrows indicate feedback inputs. Black and grey filled circles represent neural responses to stimulus preferred for neuron B before and after training.