W4L1 - Non-human primate studies of the neural basis of number processing

Question 1

Brain areas implicated from primate studies for number processing?

Answer 1

1. ) Intraparietal sulcus (IPS)
2. ) Lateral prefrontal cortex (PFC)

Other Areas:

• Superior parietal lobule (SPL)
• Ventral intraparietal area (VIP)

Question 2

The areas associated with acquired acalculia

Answer 2

Parieto-occipital junction

Frontal lobes

Question 3

How to measure neuronal responses during number task in primates

Answer 3

• Chronic implant (Animal awake)
• Measure action potentials (Single neuron localised <1mm)
• Determine “number tuning”

Question 4

3 Types of number neural coding found in single neurons

Answer 4

1. ) Numerical quantity
2. ) Proportional representations
3. ) Symbolic Numbers

Question 5

What task do we usually do in primates

Answer 5

Delayed match-to-sample task

Question 6

Delayed match-to-sample task. What are the steps involved in primates

Answer 6

1. ) Fixation (By food)
2. ) “Sample” spots flashed
3. ) Delay
4. ) 50% match/ 50% no match
5. ) If match release lever.

Question 7

Where are numeriosity tuned neruons found for delayed match-to-sample task. What are some properties

Answer 7

Lateral PFC and IPS.

• Not clustered (distributed)
• Latencies of IPS neurons shorter than PFC
  > Suggest numbers are processed in IPS (Attention) before PFC (control)

Question 8

Number tuning responses of neurons in the IPS

Answer 8

STIMULUS DEPENDENT TUNING:

• Neuron AB has a preferred tuning of 1 (Sample Presentation 500-1300ms)
• Neuron DE has a preferred tuning of 4 (Memory Delay 1300-2300ms)
• Different times for different neurons

Question 9

Does response of neurons in IPS depend on stimulus features?

Answer 9

No. Depends on numeriosity

Question 10

Number tuning responses of neurons in the lateral PFC

Answer 10

STIMULUS DEPENDENT TUNING:

• Neuron C has preferred tuning of 2
• Neuron E has preferred tuning of 4
• Tuning either transient/sustained

Question 11

What is the relationship between number tuning neurons in IPS and PFC

Answer 11

• Reponses in IPS precede those in the PFC

|&raquo_space;> Suggests feed forward from IPS to PPC; Feedback from PPC to IPS

Question 12

What are the average responses in PFC/IPS consistent with? What are some implications?

Answer 12

Qualitatively similar/ consistent with behavioural evidence (Distance Effect)

• Number tuning is not task dependent
• Average tuning is the same for sample and delayed periods
• Bandwidth of behavioural > neurons. So neurons in fact perform better than behavioural.

Question 13

Are neural responses are based on stimulus number rather than other stimulus features

Answer 13

Yes.

Other stimulus features: Area, Size, Density. Distance effect is the same

Question 14

Did the presentation of dots in simultaneous/sequential positions made a different in neural response? Where does numeriosity occur

Answer 14

• Many neurons showed response in either (small group showed both)
• Parietal lobe (Abstract: not only for one form of visual input)

Question 15

Number tuning in neurons: what does it mirror

Answer 15

• Mirror Weber’s law (imprecision increase in proportion to magnitude)
• Perceived magnitutde is a log function of stimulus intensity.

Question 16

Do the IPS & PFC have specific subregions that are exclusively for number coding?

Answer 16

No single, isolated cortical region.

• Within a cortical region, activations do not cluster neatly for a given quantitative parameter. Intermingles with neurons associated with object size&raquo_space;> part of a more general system

Question 17

Do neurons code for continuous magnitude?

Answer 17

(Length and Dots)

Some (20%) IPS neurons code for line length ratio and numeriosity, or both.

Question 18

Do non-human primate neurons show symbolic mapping onto numerosity

Answer 18

PFC neurons respond to symbolic form of number (dots and visual into number)

Question 19

What is symbolic tuning similar to

Answer 19

• Symbolic number distance effect (drop-off with increasing numerical distance)

Question 20

What is symbolic tuning similar to. How did they find out

Answer 20

Neural responses were reduced when when monkeys failed to match the correct number of dots to the learned signs.

Suggests that neurons responded to abstract numerical value rather than visual shape or dot pattern

Question 21

Implications of symbolic tuning for neurons in PFC

Answer 21

PFC neurons semantic map between signs and categories.
(2% IPS associated with symbols)

Both IPS and PFC non-symbolic
Only PFC symbolic of the IPS/PFC framework for symbols