Lecture 12: Sensorimotor Integration Flashcards
Why do we need brains and what are examples of this necessity in the smallest creatures
Sea squirts larvae have a brain (ca. 200 neurons) and can swim. They have sensory vesicles and nerve cords.
* Once attached, the animal metamorphosise into the sessile (immobile) form, and “eats” its brain.
- Animals have evolved brains to generate meaningful movement (behaviour).
How is the sensory information used to generate behaviour (for example picking up an object)?
The monosynaptic stretch reflexes is the minimal unit of sensorimotor integration:
1)Stretch of the mechanoreceptors in the
muscle increase firing rate of the afferent
sensory neuron.
2) Increased neurotransmitter release
activates the motor neuron.
3) Contraction of biceps muscle
Describe the patellar reflex/knee jerk reflex
Hit underneath the knee cap causes the leg to kick up as muscles contract due to stretch detected.
What is the reaction time due to the reflex versus voluntary movement of the contralateral leg? Is it the same for everyone?
contraction time:
reflex leg: 25 msec
voluntary leg: 170 msec
Reflex varies little within each participant (+-2msec)compared to voluntary movement (130-200msec)
What does meaningful behaviour require:
Sensorimotor integration
Selecting an appropriate behaviour will depend on…
- Context
- Internal state
- Stage in life
- Prior experience (memory)
- Current sensory information
Describe the polysynaptic reflex
1) Someone touches an iron which is very hot so dendrites of sensory neuron detect pain stimulus.
2) Axon of sensory neuron carries the signal.
3) Signal arrives at spinal cord and the interneuron excites a motor neuron causing muscular contraction.
4)The arm muscle causes withdrawal from the source of pain.
How does the polysynaptic reflex work when moving a hot object from one place to another instead of moving away from it
We need to override the reflex otherwise we’ll drop the cup. CNS neurons can affect the sensor-motor relationship of polysynaptic reflexes.
1) Axon of sensory neuron carries signal of pain.
2) An interneuron inhibits the motor neuron after muscle contraction signal is sent and this prevents muscular contraction.
How does the brain and muscles produce the behaviour necessary to play tennis?
1) Visual system: The eyes detect the ball - Cones in fovea detect light reflecting from the tennis ball, photoreceptors transduce the light stimulation into neural activity, bipolar cells
to ganglion cells then convey information to the brain.
2) Tracking the tennis ball: saccades and visual attention - The content of a subject’s visual attention can be traced from the course of that person’s saccades.
* Neurons in the posterior parietal cortex fire more vigorously when the visual stimulus are the target of saccades.
* Lesions on the posterior parietal region cause attentional deficits in humans (e.g., spatial neglect).
The saccade system keeps the image of the ball in the fovea, where vision is most accurate.
3) Trajectory prediction: integration of information over time - The prior information about where the ball is likely to bounce is from experience (memory).
* Sensorial integration produce a likelihood of where the ball will bounce.
* Using both the prior and the likelihood the brain estimates the bounce and produce
behaviour. The more experienced the player the smaller the area of likelihood.
4)Reaching and hitting the ball: The “motor homunculus” maps the areas of the motor cortex responsible for moving each part of the body.
* Specific sections of the motor cortex will be active at different stages on the approach, racquet swing and ball hitting.
Explain how eye saccades work
Superior colliculus performs visuomotor
integration.
* This region forms a map of potential eye
movement. Each neuron within the map fires
before the eyes move to the corresponding location in that map.
* Movement-related neurons: fire before saccades to specific locations.
* Visual-fixation neurons: fire after the saccade, inhibiting movements away from the target.
The caudate nucleus inhibit the tonic inhibition of the substantia nigra pars reticulata (disinhibition), which allows the superior colliculus neurons to fire and produce a saccade.
What pathways do the eyes use for tracking the tennis ball
1) Geniculostriate pathway:
* Perception of motion and depth by the dorsal visual stream (how).
* Perception of contrasts, contour and colour by the ventral visual pathway (what).
2. Tectopulvinar pathway:
* Perception of the court by the pulvinar pathway (where).
What are the loops involved in movement control + basal ganglia + describe them
1)Oculomotor loop controlling eye
movement and tracking of the tennis ball.
- Motor cortex (cortical input) -> putamen (stiatum) -> lateral globus pallidus/internal segment (pallidum) -> ventral lateral and anterior nuclei (thalamus)
2)Skeletomotor loop control voluntary
movements.
- Frontal eye field -> posterior parietal,prefrontal cortex (cortical input) -> caudate (striatum) -> globus pallidus, internal segment, substatia nigra and pars reticulata (pallidum) -> mediodorsal and ventral anterior nuclei (thalamus).
* Basal ganglia are involved in:
- action selection (as seen for the saccades before).
- Initiation and terminating actions.
- Relating actions with consequences.
What neurotransmitter is released at the neuromuscular junction for muscle contraction
Acetylcholine is released by the motor neuron axon terminal which contracts fibers in the target muscle.
Why can we not tickle ourselves
If there is no delay between the movement of the stick and tickle feeling i.e. delay of 0, it wont feel ticklish. The larger the delay the larger the response. The brain predicts the consequences of the movement of the left hand, expecting consequences on the right hand. If the prediction fails that’s when it feels more ticklish.
Describe the waitress task
Hold a heavy book with your right hand
horizontally in front of your chest (as a waitress holds a full tray).
Your task is to keep your right hand still.
Trial 1: lift the book with your left hand. Did your right hand move?
Trial 2: ask your friend to lift the book from your hand. What happened to your right hand?
When you move it the hand does not move.
When someone else moves the book, the person’s hand does move.
Describe the predictor error system
Depending on the outcome, the reward system can maintain or modify the action.
Constantly analysing the consequences of our actions.
