Chapter 37 - Functional neuroanatomy of spatial perception, spatial processes and attention

Question 1

What is hemodynamic changes?

Answer 1

Functional neuroimaging measures hemodynamic changes (of blood flow
in the case of positron emission tomography (PET); Raichle 1987), and
blood oxygenation in the case of functional magnetic resonance imaging
(fMRI) (p. 765)

Question 2

What is space representation?

Answer 2

How we see the world.

Space representation is the multicomponent experience.

Question 3

Which role does the sensory afferents have in the building of spatial representations?

Answer 3

the effects of lateralized or direction-specific stimulations of
peripheral sensory systems, with methods such as caloric vestibular
stimulation (CVS), posterior neck muscle mechanical vibration (NV), and
optokinetic stimulation (OKS)
- (meaning, that we use more than our eyes to see the world)

Question 4

So which senses do we use to make a representation of space?

Answer 4

The internal representation of space may involve the
integration of different sensory inputs - visual, somatosensoryproprioceptive,
vestibular, auditory - yielding reference frames that are
not based on individual peripheral sensory codes, organised, as they are,
in egocentric (e.g., head, trunk, arm), and object- or environmentcentered
coordinates. (p. 767)

Question 5

Which “spaces” are separately represented visually?

Answer 5

The body, the space within
reaching distance and far space. Neuropsychology and neurophysiology
provide evidence that the brain has separate representations for these
different spatial frames. (p. 767)

Question 6

What is “Personal space”?

Answer 6

Personal space is somatosensory space mapped as a body schema independently from visual space.

Question 7

What is Extrapersonal space?

Answer 7

Extrapersonal space
also involves visual space: This can be based on egocentric coordinates
(within reaching distance); visual space is organized with reference to
head, trunk and limbs. Extrapersonal space can be mapped in allocentric
(object-based) coordinates

Question 8

Which pathway maps the visual space?

Answer 8

Visual space is mapped primarily by the geniculostriate pathway where magnocellular, parvocellular and koniocellular information arrives
segregated to different layers of primary visual cortex

Question 9

Where does the V1 information project to?

Answer 9

Area V1
information is then conveyed to extrastriate visual cortex through divergent pathways, usually referred to as the ventral (object-centred or
‘what’) stream and the dorsal (space-related or ‘where’) stream p. 767

Question 10

Where are the visual cells with increasingly complex receptive field (RF)
properties located?

Answer 10

In the primary visual cortex (area V1), visual space is mapped in purely
retinotopic space. Each neuron has a receptive field, a sort of small
window which captures a portion of the visual field. - single neurons in V1 do not
discriminate between spatial locations. (example of what this means on p. 768).

Question 11

Which cells are the first cells, away from V1, that does not have apurely retinotopic mapping of the visual field?

Answer 11

the so-called gaze-dependent cells
In these cells the firing frequency depends not only on what strikes their
receptive field, but also on the position of the eyes in the orbit or the dynamic component of gaze. Initially found in the posterior parietal cortex (PPC), particularly in area 7a, and in the lateral intraparietal sulcus (LIP), they have been found in extrastriate visual areas V3, V3A, V5/MT, MST, and V6 (p. 768)

Question 12

How does the brain build an eye-position-independent

coding of visual space?

Answer 12

There are two competitive hypotheses on this issue.
1) One maintains that this further level of visual space representation
may arise by the temporal integration of an extensive system of gazedependent
visual cells
2) A second theory postulates the existence of real-position cells, in
which visual stimuli given to the same part of space cause similar
neuronal responses in spite of the actual direction of gaze and
position of the eyes in the orbits

Question 13

Where is real-position cells located?

Answer 13

Cells of this kind have been
described in the PPC (area V6a or PO, in the
ventral intra-parietal cortex and in the premotor
cortex (area F4)

Question 14

Where is somatosensation located in the nrain?

Answer 14

Cortical somatosensory representation of the body surface, joints, and
muscles includes areas of the postcentral gyrus (areas of the S1 complex,
Brodmann areas (BAs) 3, 1, 2), areas of the dorsal posterior parietal
region (BA 5 of the monkey and human BAs 5 and 7), the secondary
somatosensory area (area S2, BA 43) which is located in the ventral
bank of the parietal operculum, the granular insula, the retroinsular
cortex, and the more rostral part of the inferior parietal lobule (area 7b of
the monkey and human area 40) (p. 769)

Question 15

Which somatosensory area have the finest reception?

Answer 15

◆ S1 has the finest grained somatotopy with strictly contralateral
receptive fields and limited callosal connections.
◆ S2 has a large proportion of neurons with bilateral or even ipsilateral
receptive fields.

Question 16

Does there exist any neurons that respond to different sensory stimuli?

Answer 16

Recently, the important discovery was made of a class of bimodal
neurons which respond to visual stimuli and to tactile stimuli.
◆ the premotor cortex (area 6 or F4);
◆ the inferior parietal cortex (area 7b);
◆ the putamen

Question 17

If you should connect areas of the parietofrontral network to specific tasks, which areas does what?

Answer 17

most dorsal part of the
parietofrontal network (superior parietal cortex and dorsal premotor
cortex) is primarily concerned with reaching tasks and contributes to computing distance between target and limb, as well as spatial
location of targets.
◆ The more ventral premotor and parietal network is more concerned
with grasping, and the relevant dynamic hand-shaping processes.
Objects are therefore represented at multiple levels.
◆ In the ventral stream, objects are represented in allocentric
coordinates related to object semantics (i.e. features such as shape,
texture, colour).
◆ In the dorsal stream objects are coded for their spatial position in an
egocentric/peripersonal spatial frame used for the generation of reaching and grasping behaviour.
(p. 771)

Question 18

You want to read a discussion about spatial neglect and where it’s neuroanatomically located?

Answer 18

Do it on page 772 - 773. impossible to shorten.

Question 19

What is the Anatomical basis of deficits in reaching tasks?

Answer 19

Lesions are usually located in the superior parietal lobule, and the disorder typically involves the contralateral limb in reaching to both sides of space. p 774

Question 20

How do human and monkey data fit together regarding disorders of reaching?

Answer 20

While there is substantial
agreement for disorders of reaching, there is a clear discrepancy as far as
the location of key lesions that underpin neglect.
◆ In the monkey, neglect is more severe after ventral pre-motor cortical
lesions, than lesions in the superior temporal sulcus.
◆ In humans, the manifestations of neglect are more severe after
parietal lesions (cf. Rizzolatti et al., 2000 and Bisiach & Vallar 2000),
but not primates.

Question 21

What is the

‘what’ and ‘where’ pathways, when working with functional imaging in regard to ‘frames of space?’

Answer 21

There is a dichotomy between two visual streams.
A face matching task, utilises a ventral ‘what’ stream, and a dot location task utilises a spatial ‘where’ task.

both experimental tasks showed activation
of the lateral occipital cortex. Face discrimination alone activated a region
of the occipitotemporal cortex, whereas the spatial location alone
activated a region of the lateral superior parietal cortex.

Question 22

What is thee functional neuroanatomy of identifying / analysing object-centred (allocentric) space?

Answer 22

the lateral extrastriate cortex, of the most dorsal part of area 40 in the inferior parietal lobule, and the intraparietal sulcus, the
superior parietal lobule, and dorsal premotor cortex are involved. p. 775f

Question 23

Can you name some functional neuroanatomic differences between allocentric and egocentric tasks?

Answer 23

The premotor
cortex, the medial dorsoparietal cortex, and the right intraparietal cortex
were more active when compared with the ‘allocentric’ task. In turn,
there was a greater activation in the medial ventral extrastriate cortex
when the allocentric task was compared to the egocentric one

Question 24

What could you do to explore the egocentric (personal) space functioning?

Answer 24

map the cortical areas which are activated by either vestibular signals, or by neck muscle spindles and stimulate these to induce spatial bias towards
the stimulated side in healthy controls, and reduce spatial disorder in
unilateral neglect.

This could work since spatial representations can be achieved, is through integration via convergence of different afferent
inputs.

Question 25

What are the primary neural location of egocentric space?

Answer 25

Specific to the monkey, the perisylvian somatosensory
cortex (retroinsular cortex, area S2, supramarginal gyrus) appears to be a
site of convergence of these inputs, suggesting that these brain regions
contribute to egocentric space representation

Question 26

How would you explain what spatial attention means?

Answer 26

The space surrounding us contains far too many items for the brain to
simultaneously process efficiently and consciously at once. The mental
ability which permits people to deal explicitly with a subset of behaviourally relevant stimuli is usually referred to as attention.

Question 27

What is the difference between endogenous orienting of attention and spatial attention?

Answer 27

Endogenous orienting of attention is frequently referred to as a topdown
or controlled process which is effortful and depends on will.

Spatial attention can also be attracted automatically by the sudden
appearance of a stimulus in the visual field, or by the perceptual
salience of a stimulus among others (bottom-up)

Question 28

Does spatial attention have a dedicated neural system in the human brain?

Answer 28

Well yes and no, if you want to read a very influential hypothesis about dedicated neural systems read p. 781f,
Where 3 hypothesis are stated:
◆ The attentional system is anatomically separate from the dataprocessing
system, and in this sense it is like other sensory and motor
systems.
◆ The attentional system involves a distributed network:
— a posterior attentional system;
— an anterior attentional system;
— an ascending attentional system.
◆ Within the network, different components have different
specializations that can be described in cognitive terms

But this model is not unanimously accepted.

Question 29

What is the the physiology of eye movements and spatial attention?

Answer 29

both functions covert orienting of attention, and share neural resources in
◆ the parietal regions of the intraparietal sulcus and superior parietal
lobule;
◆ the dorsal lateral premotor cortex (human homologue of frontal eye
fields)
◆ the mesial dorsal premotor cortex (human supplementary frontal eyefields)

However! New information tells us that;
◆ Eye movements are associated with more extensive involvement of
regions near the primary motor and somatosensory cortices.
◆ Covert orienting shows a larger involvement of prefrontal, and of
lateral occipitoparietal junction regions. p. 782f

Question 30

Does imaging data agree on spatial attention and processing and the anatomy of spatial neglect correspond?

Answer 30

No.. There is a discrepancy, which could mean either that spatial neglect does not merely represent a disorder of attention. Or that some one fucked up?

The anatomy of
neglect needs to be mapped with patients performing a wider range of
tasks, to reveal dissociations of behavioural deficit.