Clinical Neuropsychology L3

changes in the sensory system in response to the environment

interpretation of the changes

* visual system: shape, form, color* auditory system: loudness, pitch

 A primary projection area (e.g., V1 in visual occipital cortex) Multiple secondary projection areas (e.g.,V3, V4, en V5supporting visual submodalities form, color, and movement) Multiple tertiary projection areas (e.g., for perception ofspecific objects like faces, hands, houses)

• Sensory systems represent the external world within the brain• There are multiple of these topographic maps for each sense• Greater number of representations is associated with greaterbehavioral complexity• The primary sensory area initially processes the information• Secondary (and higher) areas perform more elaborate processing or focus onspecific aspects of the stimulus

For example, occurrence of form blindness while color perceptionis intact; occurrence of color blindness while form perception is intact

 Cortical projections for conscious perception of stimuli (cognitive processes)

 Subcortical projections (among others to brain stem) for automatic or reflexogenic motor responses to stimuli

- Ascending bundles carry the same kind of signal, but- Encode different kinds of sensations and features of sensations

- Receptors, neural relays and cortical representations

Although experiences of e.g. vision and touch are fundamentally different, the neural input is nearly identical!

 Penfield: electric stimulation M1: ‘homunculus’ Recent: multiple representations in M1 and premotor cortex Not individual muscle control, but movement category of coordinated action (e.g. pincer grip)

controls limbs limited to one side of the body (contralateral side)

controls collaboration between both sides of the body,for example between both handsAlso coordinates movements of different limbs, like hand, arm, shoulderMental imagery!

repertoire with pre-programmed motor categories; a movement lexicon

 Simulate actions of others (action/intention understanding) Enable fast responses, anticipation Understanding emotional expressions/states Important social interaction (Rizzolatti) Or: just sensory-motor associations (Hickok)

Complex feedback circuit for intensity- inhibitory pathway- excitatory pathway

 less inhibition of the thalamus  thalamus is “free” to excite the cortex

 inhibition of the thalamus  less thalamic input to the cortex

- responsible for appropriate movement intensity ("volume control")- also involved in selection appropriate motor programs

e.g., Huntington's disease, syndrome of Gilles de la Tourette

neuromodulator, produced in substantia nigra within brain stem

• Scarcity of movements (hypokinesia, e.g., in Parkinson’s disease)• Absence of movements (akinesia), e.g., as effect of MPTP)• Persistance of certain movements due to problems with switching from one particular motor program to another one

Loss of dopamine producing cells insubstantia nigra (“black matter”)- familial or sporadicPathology: loss of neurons, which often goestogether with accumulation of “Lewy bodies”(protein clumps) in the brain- less supply of dopamine (DA) to dopaminedependent structures, like basal ganglia- hypokinetic syndrom

not curative- Physical therapy- Medication, e.g. L-dopa = gold standard- Deep Brain Stimulation (DBS) 

Contains four times as many neurons asthe neocortexDifferent parts (medial/lateral) subservedifferent movements

- Acquiring and maintaining motor skills (various skills from baseball to apping)- Activate muscles for action with correct timing and accuracy- Quick adaptation of cortical motor programs within a changing environment(implements corrections based on sensory feedback of performedmovements)

- motor coordination (ataxia, e.g., drunk's walk)- complex movement sequences- Problems with (training of) perceptual and cognitive processes

Motor commands from premotor cortex and primary motor cortex descend via corticospinal (pyramidal) tract to motor neurons within

– Brainstem (controlling muscleswithin head area: eyes, face, jaws,mouth, tongue, and vocal cords)– Spinal cord (controlling muscles oflimbs and trunk)

– Part that crosses controls limb muscles (particularly fingers)– Part that does not cross controls trunk muscles (neck, back, belly)

Anencephaly is one condition that illustrates the hierarchical organization of CNS functionInfection with the Zika virus in pregnant women can reportedly lead to insufficient development of parts/levels of the brain of a fetus.

follow maps

• Maps of the brain have been developed based on different factors, such as the structure of cells or the time of myelination• Brodmann’s cytoarchitectonic map, based on the structure of cells in different parts of the brain, remains influential• Use of MRI and newer stains have expanded the detail of the maps from about 50 areas in Brodmann’s map up to about 200 today

Projection maps of the cortex:- Primary areas; motor and sensory- Secondary areas;- Tertiary areas/cortex; ‘associative’

Multimodal sensory neurons that respond to/combine information from different senses (e.g. visual and auditory or tactile) important why?

It facilitates behaviors like memory, language, planning/initiation of complex action; ‘higher order’ functions!

- Why?Correlates with the relatively high proportion of association areas in humans- What does that mean when it comes to cortex damage and function loss?Loss of cortex function will lead to more disturbed behavior in humans than in animals!

• Research has found multiple representations of the body in themotor and somatosensory areas• Related maps are found for auditory and visual sensations• Now thought to be dozens of maps for each sensory modality• Additional maps are not duplicates of each other, but representprocessing different aspects of the sensory information

• Multimodal cortex integrates information from multiple sensorymodalities• Multimodal processing seems pervasive throughout the cortex• Research from monkeys and humans finds that speech is easier to understand if it is accompanied by being able to watch the speaker• Parallel cortical systems for perceiving and understanding the world and for manipulating the world

• Distributed hierarchical model understands that the functioning ofthe model depends on the interaction of different modules in thebrain• Brain areas are not locations where one type of information isprocessed, but part of an extended neural network that supportscognitive operations• Human Connectome Project is using resting-state fMRI (rs-fMRI) to understand the connections and networks in the brain• One study of 1000 participants identified 17 different networks• Most network are local, between adjacent areas

• Previous assumption that the brain is inactive if not engaged in aspecific activity was shown to be inaccurate• Some interconnected brain regions are active, even without aspecific task• Prefrontal cortex• Posterior parietal cortex• Posterior cingulate cortex• Medial temporal regions• Newer research has identified at least two parallel networks• Default network active during directed tasks, not just while the brainis at rest

Can form a functional network.Cortical connections can be (fig. 3.28)- Long; between different lobes- Relatively short; between parts of a lobe- Interhemispheric (commisures)- Projected through the thalamus

Representations of the external environment and experiences in thecortex

- more representations/maps means more knowledge about theenvironment and thus higher intelligence

- dynamic; an area can be part of multiple networks- resting = also activity (default mode network)- content of a cognitive process is determined by the specific activated areas 

• Our understanding of reality is dependent on the number andstructure of the cortical maps• More maps means more representations of the world and ways tointeract with the world• Rats and dogs lack color vision, altering their interaction with the world• Dogs do have better olfaction than humans, giving them an expanded understanding of the world compared to people

 More representations allow for more complex behavior

This is one of the main effects of brain damage; cognitive slowing.

How does the brain, mainly the cortex, contribute to perception of the world as a coherent whole (gestalt), not a collectionof details?