The document provides an overview of cortical sensations, detailing the posterior column and anterolateral pathways along with functionalities related to primary sensory and motor cortices. It discusses various types of sensory tests including stereognosis, graphesthesia, two-point discrimination, and sensory attention, along with the implications of impairments such as agnosia. Additionally, it emphasizes the importance of cortical regions in the recognition and interpretation of complex stimuli.

1. Cortical
Sensations
21/10/2018
Yasser Alzainy

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PosteriorColumn Pathway
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○ Proprioception, vibration, pressure, fine and
discriminative touch.
○ Three-order-neuron pathway
○ Project to:
• Somatosensory cortex.

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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}
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Classificationof Neocortex
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○ 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

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○ 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.
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○ 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.
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Neurology Department – Al-Azhar University
Testing for cortical sensation(e.g. stereognosis)
Primary Sensory Modalities
Intact
can be assessed
Impaired
Mild
depends on the judgment of the neurologist
Severe
can’t be assessed

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Cortical modalities
○ Stereognosis
○ Graphesthesia
○ Two-point discrimination
○ Sensory attention
○ Other gnostic / recognition functions
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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
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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.
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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.
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SensoryAttention
○ 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)
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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.
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Other SomatosensoryAgnosias
○ 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}.
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15. Thank You
Yasser Alzainy
010 166 202 30
yasser.alzainy@gmail.com
www.facebook.com/yasser.alzainy