CogNeuro Lectures 4-5 Flashcards
Task design of ‘which arm for which target’ study
Monkeys were given two types of information: one about what spatial target they should reach for, and information about which arm they could reach with. Either the arm→target instruction or target→arm instruction where information is separated by a delay period. In both conditions, after both pieces of information were given, there was a final delay period followed by a cue that told monkeys to ‘go’ (reach for the correct target with the correct arm)
Results of ‘which arm for which target’ study
Showed three different types of cells:
effector selective – cells that only respond to the arm instruction
“Target” selective– cells only respond to the direction of target
“Action” selective – cells that respond to both, don’t care what order is given. fires when knows full information.
Takeaway: Some neurons take in multiple types of information or information from multiple sources. The highly specific codes for information suggests that this region integrates information, as it would not be as specific without.
what was the ‘which arm for which target’ study testing?
test the information integration of target and body-part information in the premotor cortex when planning motion. Information Integration refers to the process by which the brain combines signals from multiple neurons to generate a meaningful representation.
The dorsal premotor cortex is known to receive both visual and somatosensory input, and this study shows that neurons in this area gather information about both the target and body part, while subsequent activity specifies the planned action.
What are the tasks and results in the 1-target vs 2-target task conditions?
One target task condition : simple condition, does not differentiate much from premotor or motor cortex. One target comes up followed by a memory period (delay period), go cue comes up, and then you make an eye movement to where target was
Build up cell: activity slowly rises until time of movement (build-up)
Selected-Response Cell: know from beginning target, so has sustained activity until the end in the direction of target
Two target task conditions: two targets come up followed by a delay period, go cue comes up where color indicates which target to move to.
Build up cell: activity is steady for both directions, but activity for undesired direction shuts down once known
Selected-response Cell: no activity until target is known, where activity for desired direction shoots up
takeaway: the same two neurons are responding differently depending on the number of targets. this show that the premotor cortex is selecting your motor plan.
build up cell vs selected response cell
build up cell exhibits a gradual increase in activity leading up to the moment of action
selected response cell becomes active specifically during the execution of a particular action
what areas are mirror neurons involved in?
PmV (ventral part of the premotor cortex)
Rizzolatti study : task designed to study mirror neurons
a monkey observes the experimenter grabbing peanut, which neuron activity fires. When the monkey does the behavior themselves and reaches for the peanut, the same neuronal activity fires. What drives this home is how specific the action has to be! When the experimenter simply points to the peanut, the same neuronal activity is not present anymore. They even did it in the dark to prove it is truly about that action!! They did even more complex movements with wrist rotations etc.
Caggiano study: task designed to study mirror neurons (but now testing peri- vs extra- personal space)
In the Caggiano study, the question was do PMv mirror neurons care about peri- vs extra-personal space? The peanut was now either in peripersonal space to the monkey (within reach) or extrapersonal space(too far to reach). The purpose of this is to test if the mirror neuron cares about intention; if it’s further away, you know that you cannot reach it and vice versa.
Results: some neurons were tuned to extrapersonal space (higher when farther) and some were tuned to peripersonal space (higher when closer). Evidence that some mirror neurons change how they fire based on whether the monkey might interact with what’s happening.
What is the function of mirror neurons and their potential connections to neural basis of autism?
The answer is still not known, but popular to think it is to stimulate movement for someone else! Popularized in autism research because thought that someone with autism’s mirror neurons were “wonky” (as per Prof. Chang’s words) if they could not mirror someone else’s behavior.
Another hypothesis is that this is nothing about other people, but is really about rehearsing similar movements specific neurons care about, which is more likely the case!
To test this, they looked at motor observation and motor execution in the control brain and autism brain. They had repeat (same hand movements) and non-repeat (different hand movements). Turns out that movement execution and movement observation brain activation is not different from people with or without autism.
However, they did find one thing. In the autism brain, there were more standard deviation (more variability) in the repeat condition. This suggests that the mirror neuronal system is intact in autism brains but just more variable.
How was intrinsic motivation signal in the cingulate motor area studied?
In Shima and Tanji study, monkeys were trained with 2 arm movements (push or turn a handle) and presented with visual stimuli telling them to go. Monkeys voluntarily selected which movement to perform based on a reward, and changed rewards for actions occasionally.
Results: They found that monkeys altered their movement when the reward was reduced and this triggered activity in the CMA. The neurons were quiet when they were simply told to change action (external motivation) or if they failed to change the movement.
Takeaway**: This suggests that activity in the CMA cell show activity for, and responds to, internally-generated action that is based upon perceived reward of actions (specifically related to internal motivation related activities and choices).
what is the cingulate motor area responsible for?
The Cingulate Motor Area (CMA) is an extremely important region of the brain, one that is essential for information integration and processing, and an important region involved with decision making as well. CMA is thought to be important for processing behaviorally relevant movement.
What is working memory?
the ability to temporarily hold and manipulate information for cognitive tasks performed in daily life
What is the oculomotor delay task?
In the oculomotor delay task, participants are shown a target, followed by a short delay period, and then are instructed to move their eye to where the target was on a blank screen. This tests how good their working memory is. LIP and dlPFC neurons were recorded.
What is LIP and dlPFC associated with?
Lateral Intraparietal Cortex is associated with spatial attention, saccadic eye movements, and representation of spatial information.
dorsolateral prefrontal cortex is associated with working memory processes, implicated in holding and manipulating information during delay period of tasks like the oculomotor tasks.
What were the results of the oculomotor task?
In LIP neurons, there is increased activity when the target comes up and there is sustained activity specific to that location when the target goes away.
In dlPRC neurons, there is a spike in neural activity right after the response period, indicating it may be holding information about the position of the cue in order to facilitate the later response to the correct target location, which is interpreted as a working memory signal.
Differences between the two: LIP neurons are more modality-specific (may respond less or more to eye movement vs arm movement, let’s say.) whereas dlPFC neurons respond in a higher-level manner that is less dependent on modality. This is why some people choose to interpret the signals in LIP to be more of a motor plan than a working memory signal.
