Cortical sensations

A brief lecture on cortical sensation: components, when and how to examine and involved brain areas and tracts.

1. Cortical Sensations 21/10/2018 Yasser Alzainy

2. Posterior Column Pathway Add a footer 2 Proprioception , vibration, pressure, fine and discriminative touch. Three-order-neuron pathway Project to: S omatosensory cortex.

3. Anterolateral Pathway Pain , temperature and crude touch Three-order-neuron pathway Project to: Somatosensory cortex: (spinothalamic tract) {localization} Pontine reticular formation: ( spinoreticular tract) { emotion and arousal} Mesencephalic pain modulation centers: ( spinomesencephalic tract) {pain modulation} Add a footer 3

4. Classification of Neocortex Neurology Department – Al-Azhar University 4 Primary sensory and motor cortex Primary sensory cortex Primary motor cortex Association cortex Unimodal (modality-specific) Somatosensory, visual or auditory association cortex, premotor cortex, supplementary motor area Heteromodal (higher-order) Prefrontal cortex, parietal and temporal heteromodal association cortex

5. Primary sensory areas : perceive Sensory association cortex : interpret Integrates information from more than one primary modalities Correlates the perceived stimulus with memory of past stimuli (discrimination, recognition) Crude sensations such as recognition of temperature and pain are sub-served by the thalamus and has nothing to do with the cortex which is concerned with finer aspects of sensation such as recognition of intensity, location and spatial relationships. Neurology Department – Al-Azhar University 5

6. Impairment = agnosia (loss of the power to recognize the meaning of sensory stimuli . It the term denotes lesion involving the association cortex responsible for processing the primary sensory modality. The primary modalities must be relatively preserved before concluding that a deficit in combined sensation is due to a parietal lobe lesion. Neurology Department – Al-Azhar University 6

7. 7 Neurology Department – Al-Azhar University Testing for cortical sensation (e.g. stereognosis )

8. Cortical modalities Stereognosis Graphesthesia Two-point discrimination Sensory attention Othe r gnostic / recognition functions Neurology Department – Al-Azhar University 8

9. Stereognosis Cutaneous and proprioceptive sensations Steps of object recognition Size Shape (2-D) Form (3-D) Identification of the object (memory). Each step can be assessed individually Tested only in the hands Varieties: texture recognition (cotton, wool, glass, metal) Loss = Astereognosis The earliest to be affected in parietal cortex lesion Neurology Department – Al-Azhar University 9

10. Graphesthesia Cutaneous sensation Letters or numbers drawn with blunt pin on finger pads, palms and dorsum of feet. 1 cm on finger pads Larger elsewhere Loss = Agraphesthesia / Grapheanaesthesia Varieties: tactile movement sense / directional cutaneous kinesthesia the ability to tell the direction of movement of a light scratch stimulus drawn for 2 to 3 cm across the skin), which may be a sensitive indicator of function of the posterior columns and primary somatosensory cortex. Even minimal impairment of primary sensory modalities may cause agraphesthesia . Loss of graphesthesia or the sense of tactile movement with intact peripheral sensation implies a cortical lesion, particularly when the loss is unilateral . Neurology Department – Al-Azhar University 10

11. Two point / spatial discrimination Tactile sensation . Patient education (eyes closed) 2 points 1 point 2 points so close it feels like 1. Then varied randomly and decreasing the distance till the patient starts to give errors. Result recorded as the minimum distance before the patient starts to give errors. Normal values: 1 mm at the tip of the tongue 2-3 mm on the lips 2-4 mm on the fingertips 8-12 mm on the palms 20-30 on the back of the hand 30-40 on the dorsum of the feet The most sensitive test for cortical sensory impairment. Neurology Department – Al-Azhar University 11

12. Sensory Attention The ability to perceive 2 simultaneous sensory stimuli Usually comparing 2 sides of the body (can be done on the same side); usually tested by light touch (can be done by pin prick). Loss of this function (one of the stimuli is not felt)= sensory extinction , inattention or neglect. Severity of extinction can assessed by increasing the intensity of the stimulus. Most likely due to parietal lobe lesion (can also occur with thalamic and sensory radiation lesions) Neurology Department – Al-Azhar University 12

13. Stimulus Localization Testing by asking the patient to point with his index finger to the point touched by the examiner. Accuracy varies as occurs with two-point discrimination. Loss of function: denotes lesion involving the contralateral parietal lobe. Neurology Department – Al-Azhar University 13

14. Other Somatosensory Agnosias Autotopagnosia = inability to identify body parts, orient the body , or understand the relation of individual parts -a defect in the body scheme. Hemineglect = lack of awareness of one-half of the body. Finger agnosia = inability to name or recognize fingers . {usually part of Gerstmann’s syndrome} Anosognosia = an absence of awareness, or denial of the existence, of disease. {usually found in lesions of the right parietal lobe}. Neurology Department – Al-Azhar University 14 أنا مش عارفني

15. Thank You Yasser Alzainy 010 166 202 30 y [email protected] www.facebook.com/yasser.alzainy