Pain Perception and Brain Systems

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Questions and Answers

What type of neurons in SI are primarily responsible for encoding stimulus intensity related to pain?

Nociceptive neurons (correct)

Somatosensory neurons

Motoneurons

Interneurons

What aspect of pain perception is suggested to be reflected by nociceptive neurons in SII?

Direct pain sensitivity

Attention and learning related to pain-evoking stimuli (correct)

Somatotopic organization of pain

Emotional response to pain

What phenomenon was observed regarding reaction times to painful stimuli on the left side?

Loss of short-latency responses (correct)

Increased short-latency responses

Bimodal distribution of reaction times

Immediate detection of first pain

In the context of pain localization, what does the study of Campbell and LaMotte primarily focus on?

Reaction times to laser stimulation Signup and view all the answers

What does the term 'somatotopically organized' imply about nociceptive neurons in monkeys?

They correspond to specific body regions in their response to pain. Signup and view all the answers

What is the main finding regarding pain perception in the patient with a postcentral stroke?

Discriminative and affective components of pain perception are dissociated. Signup and view all the answers

Which part of the brain is responsible for the lateral pain system?

Lateral thalamic nuclei and primary somatosensory cortex Signup and view all the answers

What is the role of Ad-fibers in pain perception according to the content?

They convey pricking first pain sensations. Signup and view all the answers

What evidence was presented for the lateral pain system's involvement in pain sensation?

Clinical examination and cutaneous laser stimulation findings Signup and view all the answers

Which components are suggested to diverge at the thalamic level in pain processing?

Lateral and medial pain systems Signup and view all the answers

In the context of the study, what does the medial pain system primarily consist of?

The anterior cingulate cortex and medial thalamic nuclei Signup and view all the answers

What physiological aspect does the study highlight about the lateral pain system?

It requires the integrity of sensory-discriminative components for first pain sensation. Signup and view all the answers

What does the integrity of peripheral somatosensory pathways suggest about the median nerve?

There is partial damage to the median nerve. Signup and view all the answers

What was the wavelength of the laser used in the stimulation?

2000 nm Signup and view all the answers

During the evaluation, how was the pain threshold determined?

Intensity that elicited painful sensations in at least three of five applications. Signup and view all the answers

How were the reaction times measured during the painful laser stimuli application?

In two subsequent runs reacting to stimuli. Signup and view all the answers

What sensory examination results indicated damage on the left side in the patient?

Abnormal responses in left-sided examination. Signup and view all the answers

What did the term 'thermaesthesia' refer to in the clinical examination?

The sense of temperature. Signup and view all the answers

What was the intended outcome of the patient lifting the index finger during testing?

To confirm sensation in the affected area. Signup and view all the answers

How often were the interstimulus intervals varied during the reaction time measurement?

Randomly, between 10 and 14 seconds. Signup and view all the answers

What was the pain threshold for the right hand as mentioned in the study?

200 mJ Signup and view all the answers

What limitations were present in prior clinical examinations of pain perception?

Non-selective pain-evoking stimuli Signup and view all the answers

What term describes the painful sensations experienced by patients in the study?

Pinprick-like sensations Signup and view all the answers

At what intensity did patients begin to describe a 'clearly unpleasant' feeling?

350 mJ Signup and view all the answers

Which area of the brain was indicated to be involved in pain processing according to functional imaging studies?

S1 and S2 Signup and view all the answers

What was the mean reaction time for the right index finger lift in the study?

300 ms Signup and view all the answers

What type of stimulation method was used in the study to selectively activate pain afferents?

Cutaneous laser stimulation Signup and view all the answers

What was a noted effect of increased pain associated with functional imaging studies?

Increased blood flow in contralateral SI and SII Signup and view all the answers

What critical factor interfered with understanding the concept of pain structures in humans?

Ambiguous clinical presentations Signup and view all the answers

What was the maximum intensity at which no pain sensation could be elicited in the left hand?

600 mJ Signup and view all the answers

What sensory response was notably absent in the tested left hand?

Response to thermal stimuli Signup and view all the answers

Which type of discrimination was significantly affected in the left hand during sensory testing?

Two-point-discrimination Signup and view all the answers

What conclusion can be drawn regarding painful stimuli detection in relation to SI and SII integrity?

Detection of painful stimuli does not require SI and SII integrity. Signup and view all the answers

Which sensory testing result was normal for the right hand?

Graphaesthesia Signup and view all the answers

What does the presence of hypalgesia in the patient suggest?

Interaction between medial and lateral pain systems. Signup and view all the answers

What was the result of motor testing for the sensory impaired left hand?

Motor reactions could not be recorded. Signup and view all the answers

Which part of the brain is suggested to be crucial for pain perception according to previous lesion studies?

Postcentral gyrus Signup and view all the answers

What type of stimuli evoked a normal response in the tests for the right hand?

Sharp stimuli Signup and view all the answers

Which stimulus did the sensory impaired left hand show no reaction to?

Thermal stimuli Signup and view all the answers

In the testing, which of the following sensory modalities had a perfect score in the right hand?

Sense of MCP joint movement Signup and view all the answers

Study Notes

Pain Affect Without Pain Sensation

A 57-year-old male patient with a right-sided postcentral stroke exhibited a dissociation between pain perception's discriminative and affective components.
The study demonstrated a dependence of sensory-discriminative pain and initial pain sensations on the integrity of the lateral pain system. This is the first such demonstration in humans.

Introduction

The brain's pain processing involves a lateral and medial pain system.
The lateral system includes the lateral thalamus, primary and secondary somatosensory cortices.
The medial system includes the medial thalamus and anterior cingulate cortex.
The lateral system is associated with sensory-discriminative aspects of pain.
The medial system is associated with emotional/motivational aspects.
Evidence from prior research in monkeys supports the association between the lateral system and sensory-discriminative pain. However, human lesion studies haven't definitively confirmed this.

Case Report

The patient experienced a cardioembolic stroke affecting the right postcentral gyrus and parietal operculum (including the hand area of SI and SII).
The MRI confirmed the lesion location.
The patient showed sensory deficits on the left side, but preserved sensory function on the right. A notable absence of pain sensation despite preserved pain affect in the patient was observed.
Thermonociceptive stimuli (laser) were used to assess and quantify pain perception. Pain thresholds were considerably higher in the affected (left) arm.
Stimulation of the right hand (unaffected) showed a bimodal distribution of reaction times, whereas the left (affected) hand exhibited prolonged latency responses.

Discussion

The observed dissociation between pain sensation and pain affect indicates the separate role of the lateral pain system and SI/SII in pain perception. Sensory-discriminative elements of pain are directly related to the integrity of SI and/or SII.
Pain affect and the ability to detect painful stimuli do not require these structures.
Cutaneous laser stimulation was a critical component in the study, as it selectively activated thermonociceptors, and thereby separated pain pathways from other sensory signals. Previous studies used nonspecific stimuli, thus potentially masking the specific functions of different pain pathways.

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Description

Explore the complex interplay between the sensory-discriminative and affective components of pain perception. This quiz delves into the lateral and medial pain systems and their roles in processing pain, particularly in relation to a case study of a stroke patient. Gain insights into how brain regions contribute to different aspects of pain experiences.