W4L1 - Non-human primate studies of the neural basis of number processing Flashcards
1.) Studies of non-human primates can inform our understanding of the neural mechanisms of number processing 2.) Two brain areas – the Intraparietal sulcus (IPC) and the lateral prefrontal cortex (PFC) contain cells that respond to number 3.) Neurons code for numerical quantity 4.) Neurons code for proportions (ratios, etc..) 5.) Neurons code for symbolic form of number
Brain areas implicated from primate studies for number processing?
- ) Intraparietal sulcus (IPS)
- ) Lateral prefrontal cortex (PFC)
Other Areas:
- Superior parietal lobule (SPL)
- Ventral intraparietal area (VIP)
The areas associated with acquired acalculia
Parieto-occipital junction
Frontal lobes
How to measure neuronal responses during number task in primates
- Chronic implant (Animal awake)
- Measure action potentials (Single neuron localised <1mm)
- Determine “number tuning”
3 Types of number neural coding found in single neurons
- ) Numerical quantity
- ) Proportional representations
- ) Symbolic Numbers
What task do we usually do in primates
Delayed match-to-sample task
Delayed match-to-sample task. What are the steps involved in primates
- ) Fixation (By food)
- ) “Sample” spots flashed
- ) Delay
- ) 50% match/ 50% no match
- ) If match release lever.
Where are numeriosity tuned neruons found for delayed match-to-sample task. What are some properties
Lateral PFC and IPS.
- Not clustered (distributed)
- Latencies of IPS neurons shorter than PFC
> Suggest numbers are processed in IPS (Attention) before PFC (control)
Number tuning responses of neurons in the IPS
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
Does response of neurons in IPS depend on stimulus features?
No. Depends on numeriosity
Number tuning responses of neurons in the lateral PFC
STIMULUS DEPENDENT TUNING:
- Neuron C has preferred tuning of 2
- Neuron E has preferred tuning of 4
- Tuning either transient/sustained
What is the relationship between number tuning neurons in IPS and PFC
- Reponses in IPS precede those in the PFC
|»_space;> Suggests feed forward from IPS to PPC; Feedback from PPC to IPS
What are the average responses in PFC/IPS consistent with? What are some implications?
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.
Are neural responses are based on stimulus number rather than other stimulus features
Yes.
Other stimulus features: Area, Size, Density. Distance effect is the same
Did the presentation of dots in simultaneous/sequential positions made a different in neural response? Where does numeriosity occur
- Many neurons showed response in either (small group showed both)
- Parietal lobe (Abstract: not only for one form of visual input)
Number tuning in neurons: what does it mirror
- Mirror Weber’s law (imprecision increase in proportion to magnitude)
- Perceived magnitutde is a log function of stimulus intensity.
Do the IPS & PFC have specific subregions that are exclusively for number coding?
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»_space;> part of a more general system
Do neurons code for continuous magnitude?
(Length and Dots)
Some (20%) IPS neurons code for line length ratio and numeriosity, or both.
Do non-human primate neurons show symbolic mapping onto numerosity
PFC neurons respond to symbolic form of number (dots and visual into number)
What is symbolic tuning similar to
- Symbolic number distance effect (drop-off with increasing numerical distance)
What is symbolic tuning similar to. How did they find out
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
Implications of symbolic tuning for neurons in PFC
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
