14- Evolution, structure/ function of the visual brain Flashcards by Anya Laila

Primates emerged how many million years ago and diversified into several lines that led to the present-day lemurs, lorises, galagos, tarsiers, and anthropoid primates?

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Evolutionary expansion of neocortex appears to be associated with changes in a functionally specific visual pathway that is linked to which type of neurons in LGN?

parvocellular neurons

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Primates emerged 65 million years ago and diversified into several lines that led to which present-day primates?

lemurs,
lorises,
galagos,
tarsiers
and anthropoid primates

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Primate brains of comparable sizes have more neurons than rodent brains . What is this called?

‘primate advantage’

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The role of the what has changed in primates with the primary target for most retinal ganglion cells the lateral geniculate nucleus?

superior colliculus

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Why are a few visual areas large while some are smaller?

large: to preserve detailed information about the visual scene

smaller areas are specialized in various ways (e.g. MT/V5).

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Bush babies (galagos) and mouse lemurs may have changed body form least from early primates.

What were the most likely characteristics of Early primates?

Small
Nocturnal
Ate insects, small vertebrates, fruits and buds
Good control of visuomotor hand movements to climb trees
Formed social groups for dilurnal living and protection

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info slide

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Through evolving, the primary visual cotex increased only slightly in absolute size while occupying proportionately much less of the total?

neocortex

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Primate evolution:
The emergence and radiation of placental Mammals (give birth) have 4 major clades including:

1- Afrotheria
2- Xenarthra
3- Laurasiatheria
4- Euarchontoglires

Which one are humans apart of

Euarchontoglires radiation (4)

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Addition of what can allow both new and original visual areas to differentiate, specialize, and develop new capacities?

new cortical areas

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Lemurs, lorises, and tarsiers are apart of the evolutionary primate group called…

Prosimians

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The oldest primate fossil found in China was known as the…

Archcebus Achilles

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Great apes, apea, and monkeys are apart of the evolutionary primate group called…

Anthropoids

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Which primate had:

Forward facing eyes and well-formed digits
Huge variation of body size

Reverted to nocturnal living. Nocturnal vertebrates use a tapetum to increase light capture which was lost in the animal when it became diurnal.

It increases eye size to catch more precise photons
It’s eyes are the same size as an orangutan & equal to its brain size

Denisovans - share 3.5% of DNA with humans (~13% with neanderthals)

The Tarsier

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Which one is not part of the primate group Great Apes?

1- orangutans
2- gorillas
3- chimps
4- humans (hominoids)
5- Lemurs
6- old/ new world monkeys
7- lesser apes

5- Lemurs
6- old/ new world monkeys
7- lesser apes

Line of apes diverged 6-8 million years ago to form chimps & bonobos and hominins (including modern humans)

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What does this term describe?

Encephalization

ratio of brain weight to body weight

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True or False?
Primate brains are generally bigger

False
Brain size is usually related to body size in animals (encephalization - ratio of brain weight to body weight)

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What does this term describe?

Encephalization Quotient (EQ)

a measure of relative brain size defined as the ratio between actual brain mass and predicted brain mass for an animal of a given size

as long as you know the body weight, you can predict the brain weight of an animal

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Recent evidence shows that mammalian brains of different sizes are not similarly scaled-up or scaled-down versions of a shared basic plan.

Different cellular scaling rules apply to rodent, primate and insectivore brains.

What species has more neurons?

Primates have a much larger percentage of neurons than rodents and insectivores

-The human brain is simply a scaled-up primate brain

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True or False:

Brain size is a good indicator of how many neurons a brain contains when compared across species

False
it is NOT a good indicator

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There is a linear relationship in primates that brain size is relitive to body mass, although humans (Homo) appear to be exception.

What is the proposed answer for why this is?

Proposed as the basis for superior cognitive abilities

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Fill in sentences:

… brains increase in size … than they gain neurons
whereas
… brain size increases in … to number of neuronal cells

This mean when comparing primate and rodent brains, … brains have a larger number of neurons than … brains of similar size

Rodent, faster

primate, proportion

primate, rodent

Which of these is not a characteristic of an early mammalian brain similar to a tenrec (hedgehog)?

-small brain with little neocortex dominated by sensory processes of V1, A1, S1
-dominated by gustatory processes (taste)
-small hippocampus (spatial memory)
-primary motor area (M1) not found in non-placental mammals
-small cap of neocortex 15 functions also identified in other clades of m’s

-dominated by gustatory processes (taste)
ANSWER: olfactory processes (smell)

-small hippocampus (spatial memory)
ANSWER: large hippocampus

What changes in the brain probably underlie differences in cognitive ability between animals and humans?

Changes in neural density

Which 2 brain areas distinguish primate brains from other animal brains?

Lateral Fissure (Sylvian Fissure): -deep groove that separates the frontal/ parietal lobes from the temporal lobe. - dividing the brain into different functional areas Calcarine Fissure: -located in occipital lobe -Responsible for vision. in the PVC

The primate brain shows a distinct pattern of layers in the lateral geniculate nucleus (LGN) with which 2 physiologically distinct pathways?

magnocellular and parvocellular

True of False: M layers have increased through size through evolution?

False, its P layers which increase

Division between magnocellular and parvocellular cells in primate brains: What are the different visual properties of M and P cells?

M: All respond equally to all wavelengths of light (don't discriminate) colour blind -very vast response to visual stimulation (good for detecting motion) -high contrast sensitivity (MGC pulls info from large areas of rods and cones) -low spatial resolution (dont know where photons are coming from due to gathering from large surface area) P: - colour-sensitive -slow -low contrast sensitivity -high resolution From there, projections in to layers 4c alpha and 4c beta Direct projection to MT in humans (movement) V2 cells have banding of colours, form, and stereo

Primate brain: Visual cortex Early primates characterized by large visual cortex divided into number of areas. Which areas is 2-3 times larger than expected for mammals of similar body size?

All primates have a large primary visual area (V1) Area V1

In primates (apes) 80% of ganglion cells are which type of cells?

parvocellular cells - colour-sensitive -slow -low contrast sensitivity -high resolution (getting their output from cones/ small receptive fields)

Primate brain: Visual cortex Primates and tree shrews have orderly arrangement of orientation-selective neurons in V1. What does this mean?

Creates occular dominance maps -Primates input of the eye at the LGN input of eyes are separated. relates to the contralateral and ipsilateral terminate in layer 4 forming ocular dominance columns (to keep eye of origin separate). V1 gets bigger with brain size, but only up to great apes. Larger human brain has V1 of similar size to a chimpanzee - V1 size in humans actually decreased relative to other primates. V1 of primates differs to other mammals by having more neurons for its size (increased density). High densities of small neurons provide a framework for preserving the details of visual scenes V1 specialized for detailed vision in all primates, especially Old World monkeys, apes and humans.

Are retinal projections in primates the same as in other species? These were the 3 pathways in primates: midget ganglion cell -> parvocellular pathway (P) parasol ganglion cell -> magnocellular pathway (M) small ganglion cell -> koniocellular pathway (K)

In many species K and M classes dominate, and P class is a small %. But in primates 80% of ganglion cells are P class. In mammals, most RGCs project to superior colliculus (SC), but in primates nearly all RGCs project to the LGN, with virtually all P cells following this pattern. The role of P cells has dramatically changed - primary target now LGN and not SC (when moving from mammalian brain to primate brain) SC in primates connect to motor neurons in the brainstem that mediate eye and head movements, so that central vision is directed toward objects of interest.

Has evolution acted on any specific brain areas of pathways in the brain if so is this linked to any specific behaviour? This is done by: Brain volume data available for 34 species - V1, LGN and neocortex Brain data available for 14 species - number of neurons and volume of separate magnocellular and parvocellular layers of LGN Need to show that similar regimes of NATURAL selection produce similar traits in separate taxa, i.e. the traits have evolved together in different lineages. This discriminates between common inheritance and independent evolution. To answer this what do we need to calculate:

‘relative size’ of a brain structure - contrast the volume of brain structure of interest (e.g. V1) with rest of the brain [brain-(neocortex+LGN)] and ‘encephalization’ - brain size relative to body size

Are visual brain structures disproportionately expanded in species with large brains? What is the relationship between brain size and visual specialization for Parvocellular neurons

-the sizes of LGN, V1, and neocortex are positively correlated with encephalization -the relative number of parvocellular neurons in the LGN is positively correlated with encephalization Expansion is only specific for P layers

The visual specialization underlying encephalization is specific to which system?

parvocellular

Researchers found a strong positive correlation between relative neocortex size and relative number of which type of neurons?

parvocellular

Which type of layers of LGN have not evolved with total neocortex size?

magnocellular

The expansion of... appears to be associated with changes in a functionally specific visual pathway that is linked to ... neurons in LGN?

neocortex, parvocellular

Which of these factors does not imply that the neocortical evolution is intimately associated with visual specialization: parvocellular LGN size in primates diurnality (activity during day time) frugivory (plant-animal interaction) social group size contrast sensitivity threshold relative neocortex size

contrast sensitivity threshold

Correlations between which 2 have been interpreted as evidence for selection on social cognition? parvocellular LGN size in primates diurnality (activity during day time) frugivory (plant-animal interaction) social group size contrast sensitivity threshold relative neocortex size Animal posture

social group size and neocortex size

Which of the following is not included in parvocellular processing of fine details: processing static social stimuli facial expressions gaze direction posture subject/object interaction

processing static social stimuli X its dynamic

parvocellular processing of fine details is likely to occur in extra-striate areas such as ...?

inferotemporal cortex (IT)

Primate extra-striate cortex contains a large number of smaller specialized visual areas - an example is MT (called V5 in humans) Fill in the sentence: MT easily identified in primates (monkeys) by its projection pattern from ... is dominated by relay of the ... pathway though V1. These are found in all studied primates, including humans, but not in ...

V1, M-cell tree shrews, rodents, or rabbits

What is the name of the visual area that first evolved in early primates?

MT (motion)

Lesions to MT lead to severe deficits in perceiving ...?

visual motion holistically (u can still see individual dots moving but not all dots in a coherent direction)

Microstimulation of which area produces visual motion perception?

A patient with bilateral lesions to MT can no longer perceive motion, they instead see objects moving in snapshots. What condition is this known as?

akinetopsia

A patient has static objects appear at various locations along their trajectories. What condition is this known as?

akinetopsia

Selective disruption of V5 (Homolog of MT) interferes with the ability to perceive? sense of touch sense of smell sense of motion

motion

Area MST is particularly selective in motion (picks up motion when you are walking around) what is this known as?

Optic Flow

What are the 2 pathways primate brains contain beyond V1?

Ventral stream - object recognition Dorsal stream - spatial perception and motor planning

Which pathway beyond V1 in primates has its main input from the parvocellular system?

ventral stream - object recognition

Which pathway beyond V1 in primates has its main input from the magnocellular system?

Dorsal stream - spatial perception and motor planning

Which lobe in primate brains is connected to the ventral stream?

Temporal lobe - specialized areas for different sorts of objects such as faces - P cells

Which lobe in primate brains is connected to the dorsal stream?

Parietal lobe - many specialized areas for using visually guided actions in space - M cells

What happends in ventral pathway and neurons in inferotemporal (IT) cortex in the mokey and human brain?

-Cells in the inferotemporal cortex of the monkey brain respond to faces from the same species and to related stimuli -The human brain has a region of extra-striate cortex that is specifically and reliably activated by faces (only kept relevant types of visual stimuli like motion and facial recognition)