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? Include the “other areas”
- 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
3 types of number neural coding found in single neurons
- Numerical Quantity
- Useful to estimate number
- Compute Exact Number
-
Proportional Representations
- Judgement of relative size
- Not necessarily symbolic
-
Symbolic Numbers
- Communication
- Language
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 for food
What are some properties of numeriosity tuned neruons found for delayed match-to-sample task.
- ) Where are they found
- ) How are they distributed
- ) What is the latency
- ) Specificty
- Numerosity tuned neurons abundant in the lateral PFC and IPS
- Number selective cells are distributed, not clustered
- Average latency of IPS neurons shorter than PFC
- Responses in IPS precedes PFC
- Suggest numbers are processed in IPS (Attention) before PFC (control)
- Neurons are not specific to a single number, but they have a preferred stimulus tuning
Number tuning responses of neurons in the intraparietal sulcus
Clear evidence of stimulus dependent tuning
- Preferred number tuning
Evident at different times, for different neurons
- Some for sample
- Some for delay
Responses depend on numerisoity than features
Number tuning responses of neurons in the prefrontal cortex
Clear evidence of stimulus dependent tuning
- Preferred number tuning
Transient or Sustained
Responses depend on numerisoity than features
Average responses in PFC consistent with behavioural performance.
- ) What kind of distance effects do neurons show
- ) What is the average tuning depending on task
- ) What is the number tuning qualitatively similar to
- ) Can we predict behavioural from neuronal pattern?
- Average number tuning shows distance effect
- Weber’s Fraction
- Number tuning is not task dependent
- Average tuning is the same for sample and delayed periods
- Number tuning of neurons is qualitatively similar to behavioural performance
- i.e., poor tuning = poor performance
- Bandwidth of behavioural > neuron
- At a neuronal level, single neurons perform better than a monkey performs behaviourally
Are neural responses are based on stimulus number rather than other stimulus features
Yes.
- Despite changing feature properties (area, size, density), the number tuning drop off is similar
- Suggests these neurons were not tuned to properties apart from numerosity
Did the presentation of dots in simultaneous or sequential (basic arithemetic) positions made a different in neural response?
- Many neurons showed response in either
- Tuning for simultanenous but not sequential
- Tuning for sequential but not simultaneous
Non-symbolic number tuning in neurons: How does it mirror Weber’s Law and the Log Number Line?
Weber’s law
- Numerosity not coded by neurons in an exact manner
- Imprecision increase in proportion to magnitude
Logarithmic number line
- Symmetric number tuning functions are only obtained after log transformation of the number scale
- Coconsistent with Fechner’s law, which states that the perceived magnitude is a logarithmic function of stimulus intensity
- Found up to 30 items for non-human primates
Do the IPS and PFC have specific subregions that are exclusively for number coding? What does it suggest?
No single, isolated cortical region
- Within IPS and PFC, activation do not cluster.
- Neurons with object size and other properties intermingled with number tuned neurons in the same vicinity
- Suggest that number neurons are part of a more generalised analysis
Do neurons code for proportions/continuous magnitude? What is the study and results?
Task: Compared number tuning and line length tuning
- Some (20%) of anatomicaly mingled IPS neurons encode either line length ratio, numeriosity, or both.
- Interminged
- No one region where it is “line-selective” or “numeriosity-selective”
- Not clustered together
- Proportionals might have evolutionary benefits
Do non-human primate neurons show symbolic mapping onto numerosity? Where?
- Relatively large proportion of PFC neurons respond to symbolic form of number (dots into number)
- PFC encodes dots and visual sign as numerical values
- PFC for abstract associations
What is symbolic tuning similar to (neurons)
Symbolic number distance effect
- Drop-off with increasing numerical distance from preferred numerical value
- Trial by trial activity of neurons correlated with the monkeys’ performance
- Neural responses were reduced 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 and IPS
Both IPS and PFC non-symbolic
But only PFC symbolic of the IPS-PFC framework is engaged in semantic shape-number associations in symbol-training monkeys
- IPS
- Non-Symbolic
- Does not seem to be associated with symbols (Only 2%)
- Quality of neuronal association in the IPS was weak and occurred much later during the trial (could have been feedback).
- PFC
- Semantic mapping between signs and categories
