Higher Visual Areas & The NCC Flashcards
What does the extrastriate cortex contain?
It contains at lease four separate visual areas
What has future research identified in the association cortex?
It’s physiological properties which are divided up into fields of common functionality
What is a connection between two cortical areas considered to be?
Ascending or forward if axons predominantly terminate in layer 4
What does a descending/feedback connection entail?
The axons avoid layer 4, targeting the upper layers instead and, on occasion, layer 6.
What is a key characteristic of the termination zone of axons?
Their function to feeding back information from a higher to a lower level is wider than that of forward projecting neurons, making excitatory synaptic contacts
What are lateral connections?
Where cortical areas are coupled at the same level in the hierarchy
How can the hierarchal organisation chart be described?
It holds dozens of levels that resemble a maze of steam pipes in an old industrial plant, highly intricate, with myriad bypass, shortcuts, and seemingly random additions
How many areas of the cortex have been reported so far?
1/3
What does the top of the hierarchal figure represent?
Either outside the cortex proper or onto regions in the frontal part of the brain and from there to the motor structures that execute the brain’s commands
What does every cortical area do?
Send it’s axon outputs out somewhere
What is research uncertain of in terms of the connections between inferior temporal, posterior parietal, and prefrontal cortical regions?
The uncertainty of whether forward and feedback cortico-cortical projections can be identified in the front of the brain
What is important to note about visual stimuli?
All areas at any one level are not simultaneously excited by visual stimuli
Where do temporal differences remain evident in regards to cellular stream flow into V1?
In the further processing stages, such that the frontal eye fields in the front of the brain receive visual information prior to areas V2 and V4 at the back
What is the net-wave?
The rapid increase in stimulus-triggered spiking propagates through the stations along the visual hierarchy without appreciably changing the steepness of the wave’s leading edge
What is the detection of a net-wave deep in the cortex?
It’s detected with a jitter of 10 msec or less
What is the argument surrounding forward travelling net-wave?
It can rapidly trigger quite complex, yet unconscious, behaviour, while consciousness depends on some sort of standing wave between the back and the front of the cortex
Where are all sensory modalities relayed through?
The thalamus on the way to the cortex
What is the structure of the thalamus?
It is subdivided into discrete nuclei, each with their own, separate input and output channels and unique functional correlates
What is the largest nucleus?
Pulvinar
What is the structure of the primate pulvinar?
It is partitioned into four divisions with at least three separate visual maps
What is an example of engaging the switching capacity of the thalamic region?
Staring intently at foliage because you might have seen somebody hiding there or scanning the road ahead of you
How do core cells operate?
They aggregate in clusters and target precisely delineated recipient zones in the intermediate layers of cortical regions
Where to matrix projection cells reach?
In a more diffuse manner into the superficial layers of several adjacent cortical areas
What is the role of the matrix?
Might help assemble the widespread neuronal coalitions that mediate the multi-faceted aspects of any conscious percept
How is the primary forward response modulated?
Through mediation of some of the observable nonclassical receptive field effect via feedback from the middle temporal cortex to V1
What are forward projections thought as?
Strong, driving connections
What does feedback modulate?
The response of recipient cells, setting the magnitude of the neuronal response
What is the rule for weaker, modulatory connections?
A thalamic input into layer 4 or the lower part of layer 3 is usually a strong connection
What is the key emerging conclusion when considering the connections in the brain as binary?
There appear to be no strong loops in the cortico-thalamic system meaning there are no thalamic or cortical areas that are directly or indirectly, recurrently connected via strong projections
What do strong reciprocal connections promote?
Uncontrollable oscillations such as epilepsy
What is an example of a key experiment in visual abilities?
The visual abilities of monkeys with inferotemporal lesions were compared against those with destruction of their posterior parietal cortex
What has the data from neurological patients with focal brain damage concluded?
That IT contains circuitry specialised for the discrimination and recognition of objects while PP is necessary for computing spatial relationships to guide the eyes or a limb to a target.
What is another name for the ventral and dorsal streams respectively?
Vision for perception AND vision for action pathways
Where do the cross linkages for the ventral and dorsal streams lie?
At the interface between the two pathways
What belongs to the frontal lobes?
Motor, pre-motor, prefrontal & anterior cingulate cortices
When does the prefrontal cortex act solely by itself?
For high-level, executive functions
When does the PFC increase in size?
During phylogenetic development
What are the frontal lobes related to?
Basal ganglia, large sub-cortical structures,
How does the basal ganglia project back to the cortex?
Via intermediate stations that include the thalamus
What is the basal ganglia drastically affected by?
Disorders such as Parkinson’s or Huntington’s disease, associated with severe motor deficits, up to a total loss of movement
What isn’t thoroughly suppressed by V1 inactivation?
Cortical motion area MT
What is a key observation found in regards to MT cells?
Lesioning the corresponding regions in both V1 and the colliculus eliminates all responsiveness from MT cells
What is the subcortical bypass adequate for?
Supporting minimal, unconscious visuo-motor behaviours of patients whose V1 has been destroyed, yet insufficient to power the ventral pathway responsible for conscious object vision
What is a fair comparison between V1 and V2?`
V2 has the same skewed topographic representation found in V1, with many more neurons dealing with central than peripheral vision
What do modern cartographic techniques utilising fMRIs confirm?
The human occipital lobe holds multiple representations of the world, similar to those that are discovered in a monkey using microelectrodes
What do V2 cells respond best to?
Short bars, lines or edges
What can illusory edges do?
Delineate a shape, such as a triangle, that doesn’t exist on the page
What are illusory edge neurons responsible for?
Identifying partially occluded figures
What reinforces the physiological data on the role V2 plays in vision?
Behavioural evidence from monkeys whose V2 has been selectively destroyed
What regions have their own retinotopic representation?
V3A and V4
What are colours the product of?
The mind and not of the external world
What does perceived hue depend on?
The relative activity in the different cone photoreceptor populations
What does colour constancy entail?
Large changes in the spectral composition of the light source causes only minor changes in the colour appearance of objects
What is the difference between V1 cells and V4 cells in terms of their relationship with wavelengths?
A double-opponent cell in V1 may fire whenever a set amount of, say, middle wavelength light impinges onto its receptive field, whereas a V4 cell responds to the middle wavelength region of the spectrum within its receptive field relative to the spectral distribution of stimuli in an extended region of the entire visual field
What happens to patients with achromatopsia?
Hue perception is gone
What has functional brain imaging established?
A number of regions in the cortex that are selectively active during colour perception and colour judgements
What is negative afterimage?
When you stare at a saturated colour and then look at a uniform grey field, you will see its complementary colour
What does the fMRI activity in a part of the fusiform gyrus following the percept showcase?
Increasing in response to the virtual colour afterimage and decreasing back to baseline within a short time after the inducing colour patch has been removed
What is colour-hearing?
Certain words, sounds, or music consistently evoke particular colours
What is the similarities between synaesthesia and colour hearing?
It is automatic, involuntary, and stable across many years
What does the V1 and V2 fMRI response reinforce?
The specificity of the fusiform region for hue perception but also the claim that the NCC for colour does not have to relay on V1 activity
What is the middle temporal area?
A small piece of cortical real estate, the size of a thumbnail
What happens to neurons in MT cells?
They retain selectivity over a considerable range of speeds, stimulus sizes, and positions
Where were MT cells only found in past research?
In corpses
What has improved the finding of localised MT cells?
MRI
How can a motion aftereffect be induced?
To gaze, for a minute or so, at the centre of a rotating disk with spirals painted on top
How can the neural substrate of illusory motion be visualised?
Using fMRI which illustrates the subtlety of the mind-body interface
What can cause akinetopsia?
The loss of MT and other nearby regions on both sides of her brain to a vascular disorder
How does a monkey react when a cell responds to a larger than average number of spikes?
The monkey tended to choose that cell’s preferred direction of motion on that trial, which implies that behaviour can be influenced by individual cortical neurons
What have modelling studies shown monkey decision being based on?
The weakly correlated activity of less than 100 MT cell
What is functional microstimulation a testimony of?
The columnar properties for motion
What is the consequence of microstimulation equivalent to?
Increasing the motion signal in the upward direction by some fixed amount
What is the electrical current of microstimulation too weak for?
Triggering a precept, such as a moving phosphene, but it can influence its attributes
What is the structure of the MT area?
A columnar structure for direction-of-motion, suggesting that this attribute is made explicit in the firing rate of these cells
What type of interactions do MT cells have to take with other regions for motion awareness to occur?
Bidirectional
Where do MT cells project?
Not only out of the cortex, but also to the frontal eye fields and to several motion-sensitive areas in the posterior parietal cortex, including the lateral and ventral intraparietal areas and the medial superior temporal area
What do the cells in MST respond selectively to?
Different optical flow fields generated by navigating through the environment
What is a sufficient method of mediating a rapid behavioural response?
The advancing front of the net-wave triggered by motion onset and flowing from the retina through V1 and into MT and beyond to other dorsal regions
What does the external electrical current delivered to the MT generate?
A bias signal that influenced the behaviour and the depth perception of the animal, depending on the disparity tuning of the neurons near the electrode tip
What is the posterior parietal cortex implicated in doing?
Combining and expressing position information and in relating it to action
What is PP subdivided into?
Half a dozen functionally distinct regions in the macaque, and more refined techniques keep uncovering additional ones
What type of movements to cells encode in monkeys?
Movements that they plan to execute within the next few seconds
What is neglect and optic ataxia characterised by?
- Severe disturbances of spatial awareness
- Persistent inability to reach out or point to targets
What is the gain field strategy?
The output, or gain, of the receptive field is modulated by the position of the eye
How can location be recovered?
By combining signals from many such cells
How can relative position be tested?
By assessing the coordinate system underlying spatial awareness and contrasting them with those controlling visuo-motor behaviour
How do place cells operate in the rodent hippocampus?
They fire maximally when the animal is physically within a particular region in its environment
What is the pathway of the ventral stream outside of the V1?
A series of stages through V2, V4 and the posterior inferotemporal cortex, until it arrives at the most forward, anterior part of the inferior temporal cortex
What does the feedback from the medial temporal lobe serve to?
Retrieve visual memories and load them into IT
