1. pg. 379, figure 1-Can you explain the take-home message of this slide?
This shows specific examples of the power function relationship for various stimulus
modalities. The subjective intensity on the y axis was assessed in this case by asking the
subjects to rate the intensity as the force they produced (hand pressure) which was
quantified by a strain gauge. Take home message is: the perceived intensity of a stimulus
is a power function of the intensity of the delivered stimulus and that different modalities
have different powers (slopes).
2. pg. 399, figure 1-What is the purpose of inhibitory surround? Can you give a
brief explanation of this figure?
Part A illustrates typical shapes and sizes of cutaneous mechanoreceptors on a monkey’s
hand and arm showing decreasing size peripherally on the digits. B1 shows idealized
relationship of excitatory (x) and inhibitory zones of the receptive field of a neuron in SI
cortex. B2: hypothetical records showing responses (action potentials represented by
short vertical lines) of a SI cortex neuron to mechanical stimulation of the skin . A
stimulus applied steadily to the excitatory part of the receptive field elicits a steady firing
in the cell. When the inhibitory region on the skin is stimulated along with the excitatory
part, the excitation is inhibited. B3: simplified model of the input connections for a cell
in the dorsal column nuclei with a receptive field that has an excitatory zone and an
inhibitory surround. The circuitry drawn shows how a stimulus applied to the inhibitory
surround would excite a different set of neurons in the DCN and that these inhibit the
central cell via excitation of inhibitory interneurons (black).
A purpose for inhibitory surround is illustrated in the following 3 figures – to maintain
small receptive field size thus allowing good spatial acuity.
3. pg. 424, figure 2-What is the difference between Nociceptive Specific and Heat,
Pinch Cold neurons?
heat, pinch cold neurons are nociceptive specific neurons that also respond to very cold
(noxious) stimuli
4. pg. 427, figure 2-Can you explain what this figure shows?
This figure shows sets of 2 images of the brain under different stimulus conditions. Each
image is a horizontal section through the brain and the bright parts show regions of the
brain with increased blood flow. Increased blood flow results from increased neural
activity. The top row shows cingulate cortex activation (arrows), the bottom row
activation in the insular cortex. The 5 conditions are – a noxious thermal stimulus at 5
degrees, a slightly cold (cool) stimulus (20C), a combination of alternating cool and
warm bars (20 and 40C), a warm stimulus (40) and a noxious hot stimulus (47C). If you
place your hand on a grill of alternating warm and cool bars the sensation perceived is
that of a very hot, painful stimulus even though there is no very hot stimulus applied to
the hand. This is known as the thermal grill illusion of pain. What the PET images
reveal is that under the grill condition both the insula cortex and cingulate cortex are
activated, similar to the case when noxious cold or hot stimuli are used but different from
what is obtained when only a warm or cool stimulus is applied to the hand.