Lecture 1: Neurons Lecture 2: Coding with spikes Lecture 3: Tuning - PowerPoint PPT Presentation

Lecture 1: Neurons Lecture 2: Coding with spikes Lecture 3: Tuning curves and receptive fields Lecture 4: Population vectors To gain a basic understanding of how population vectors are constructed

4 credit students: First assignment is posted. You have one week to work on it. You can work in groups as long as all contribute and each student submits its own write up. There will be a doodle-poll link posted to schedule meetings to talk about the assignment. Please fill in your available times as soon as possible.

Firing frequency 90 o up  0 o left 180 o right 369 0 45 90 135 180 225 270 Movement angle “Best” angle for a given cell (angle s max that elicits maximal response r max )

Vectors

20 90 o Firing frequency y 15 s 3 s max = 135 o 10 Hz 10 5 Movement angle 0 135 o 0 45 90 135 180 225 270 369 180 o 0 o x s 0 s 1 s 2 s 3 s 4 90 o 90 o y y s 2 s 4 10 Hz 10 Hz 135 o 135 o 180 o 180 o 0 o 0 o x x

90 o y N 3 N 4 s max (N 1 ) = 40 o Firing frequency N 5 N 2 N 1 s max (N 2 ) = 110 o 10 s max (N 3 ) = 135 o s max (N 4 ) = 180 o N 2 N 3 s max (N 5 ) = 230 o 0 45 90 135 180 225 270 369 N 1 180 o 0 o N 4 x N 5 s1 s2 s3 90 o 90 o y y N 3 N 2 N 2 N 3 N 2 +N 3 180 o 0 o 180 o 0 o x x

N 3 N 5 N 4 N 3 N 4 s max (N 1 ) = 40 o N 1 Firing frequency Firing frequency N 2 N 5 N 2 N 1 s max (N 2 ) = 110 o 10 10 s max (N 3 ) = 135 o s max (N 4 ) = 180 o s max (N 5 ) = 230 o 369 369 0 45 90 135 180 225 270 0 45 90 135 180 225 270 s1 s2 s3 s1 s2 s3 90 o 90 o y y N 3 N 2 N 2 180 o 0 o 180 o 0 o x x

Exercise: You recorded from three neurons during a monkey’s movement. You have approximated each response curve with a cosine function. Each neuron’s response is normalized to its OWN maximal response. A B C 1.0 Normalized firing rate 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 20 40 60 80 100 120 140 Movement angle

A B C 1.0 Normalized firing rate 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 20 40 60 80 100 120 140 Movement angle You now use your recordings to predict what the monkey is going to do. The numbers I will give you will be in normalized firing rate. You record the following: A = 1.0, B = 0.0, C = 0.0. What is the best estimate for the angle of movement?

A B C 1.0 Normalized firing rate 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 20 40 60 80 100 120 140 Movement angle You record A = 0.9, B = 0.6. Use three different methods to estimate the angle of the movement from these numbers. Discuss which is best and why.

A B C 1.0 Normalized firing rate 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 20 40 60 80 100 120 140 Movement angle You record A=0, B = 0.6 and C = 0. What is your best estimate? How accurate do you think this could be?

A B C 1.0 Normalized firing rate 0.9 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 0 20 40 60 80 100 120 140 Movement angle You notice that all your predictions are off by several degrees. State several reasons why this could be the case. How well would a labeled line vs population code decoding strategy work in this case? What would happen if you could increase the number of neurons by 100 fold?

Yellow light ~ 590 nm R nm 425 525 625 G B

Deuteranomaly, caused by a similar shift in the green retinal receptors, is by far the most common type of color vision deficiency, mildly affecting red–green hue discrimination in 5% of males. It is hereditary and sex-linked.

Yellow light ~ 590 nm R 425 525 625 nm G B R G 425 525 625 nm angle is close B

Red light ~ 625 nm R 425 525 625 nm G B R G 425 525 625 nm Angle is changed, color perception changes B

J. E. Lewis Sensory processing and the network mechanisms for reading neuronal population codes

a , Schematic of the local bend network that processes the location S of a touch stimulus to produce a bend directed away from the touch. The network is contained in a single segmental ganglion of the leech nervous system. There are three layers of neurons in the network. The number of neurons at sensory and motor levels is indicated by the number of circles. The exact number of interneurons is not known, although 17 have been identified so far 8 . b , The tuning properties of the mechanosensory P neurons to stimulus location. Shown are curves fitted to data described in Lewis 9 and given by P i ( S ) = * )) where S is the stimulus location, P i ( S ) is the F (cos( S - P i normalized spike count, F ( x ) = 0 for x 0 and F ( x ) = x for x > 0. The perimeter of the cross-sectional body wall is roughly circular. We define a location = 0° as the dorsal midline, = 180° = -180° as the ventral midline and = -90° and = 90° as the left and right lateral midlines, respectively. c , To emphasize the directionality of the neural responses and to allow comparison with the behavioural responses discussed later, the same P neuron tuning curves are expressed in a polar coordinate system. The P i * are the stimulus locations where the * = peak response occurs (that is, preferred locations). P i (45°,135°,-135°,-45°) for i = (1,...,4).

In all panels, solid lines drawn in the polar coordinate system are unit vectors (directed toward the origin) corresponding to the bend direction. Dotted lines correspond to the mean bend direction. a , The responses to a touch stimulus at S = 45° (denoted by the arrow). b , The responses to intracellular current injection in the P2 neuron (denoted by the icon). c , The responses elicited by simultaneous delivery of both stimuli. The data shown are from 15–16 trials in four animals.

a , Summary of the errors produced by the model for different numbers of interneurons ( N I) and noise levels, k . Also shown for reference are the experimentally measured behavioural error (dotted line) and the P neuron decoding error (solid line). The filled circles show the results for zero noise level ( k = 0). b , The minimum number of interneurons ( N I) required so that the model is more accurate than the experimentally observed behaviour. Minimum N I increases almost linearly with the noise level. c , The responses of the model ( N I = 16) for 20 trials at a stimulus location of S = 90° (compare with Fig. 2c).