sensory intergration and perception

what is the cortex?

• the rind of the brain

• 2-4mm thick

• 40% of mass, 14-16billion neurons in human brain

• 90% of cortex is neocortex

• 6 layers 

what are pyramidal cells?

• pyramid shaped

• large apical dendrite pointing towards cortical surface and multiple basal dendrites

• projects to outher cortical layers 

• layers III and IV (output)

• excitatory (glutamatergic)

• input from stelate cells and inhibitory interneurons

• corticospinal and corticalbulbar pathways 

what are stellate cells? 

• star shaped, short and radiate in all directions (no apical)

• local circuits

• granual layer IV (input) of neocortex

• receive thalamocrtical sensory input

• excitatory (glutamatergic) local processing of thalamus, can also be inhibitory

• connect to pyramidal cells

what are the 6 layers of the cortex?

1. molecular layer

2. external granular layer

3. external pyramidal layer

4. internal granular layer

5. internal pyramidal ayer

6. multiform layer

what is the role of layer I?

• axons and dendrites, few neurons 

• intergration

what is the role of layer II?

• small pyramidal and stellate cells 

• input from other cortical areas, local cortical processing 

what is the role of layer III?

• medium pyramidal cells

• input from other cortical areas and outut to other cortical areas 

what is the role of layer IV?

• stellate cells 

• sensory relay from thalamus 

what is the role of layer V?

• large pyramidal cells (betz cells in motor cortex)

• outut to subcortical targets, major motor output 

what is the role of layer VI?

• mixed neurons 

• output to thalamus 

what brodmann area is the primary visual cortex?

17

what brodmann area is the primary auditory cortex?

22

what brodmann areas the primary somatosensory cortex?

1, 2, 3a and 3b

what brodmann areas are the somatosensory association areas?

5 and 7 

why is the sensory homonculus problematic?

• assumes the white male body is universal 

• women 50% more likely to have a heart attack 

• pulse oximeters are less effective in people with darker skin

what type of organisation is the cortex mapped into?

columnar

• vertical columns of neurons that span 6 layers 

• a column is a functional unit of informational processing 

• allowed rapid expansion of cortex 

how can S1 be divided into inividual somatotopic maps of the contralateral body?

• 3b sends into to 1 and processes cutaneous tuch 

• 1 projects to association areas which process texture, shape and fine tactile features 

• 3a sends info to 2 about joint and muscle signals 

• 2 projects to associayion areas about size, shape, position of objects (proprioceptive and tactile info)

• this info is processed sequentially (e.g 3b input to 1) and in parallel (different types of info are processed at the same time, e,g 3b vs 3a)

what are feature detecting neurons?

neurons that respond selectively to specific characteristics of a sensory stimulus e.g orientation, shape, texture, location

e.g area 1 processes texture, area 2 processes shape and size 

what does feature detection rely on?

convergence- multiple lower level neurons synapse onto a higher level neuron

feature detection depends on combining simple inputs to recognise patterns, edges or directions 

what is the role of association areas?

• association areas intergrate information from multiple regions

• they allow sensory stimuli to be recognised, affixed meaning and value 

• the human brain is 80% association areas

what are the somatosensory association areas?

brodmann areas 5 and 7

what is the role of the somatosensory assoiation areas?

• allows multisensory understanding of world and predicting future

• strong connections to hippocampus and amygdala 

• stimulating sensory areas creates complex sensory experiences

what happens when the primary somatosensory area is damaged?

loss of ability to detect sensory stimuli

what happens when the somatosensory association areas are damaged?

issues with recognition and perception

• astereognosis = inability to identify objects by touch alone without the use of sight

• hemineglect = failure to be aware of one side of space, usually when right hemisphere is damaged