COGS 107B Systems Neuroscience
March 11, 2010
To prepare for the exam, study principles of the week and terms you should know
REVIEW
Fire together, wire together
connection strength between neurons can depend on co-activity patterns of two neurons
Changes in strength of connection = synaptic efficacy
pre-synaptic neuron fires action potentials…the amount of depolarization in post-synaptic neuron can
change
depends on timing and order of firing
spike-timing dependent plasticity (STDP)
(slide with graphs of STDP curves is a great simplification)
Memory
Know difference between implicit and explicit memory
Associative – e.g. conditioning, can be implicit or explicit
Procedural – motor and perceptual skill learning, implicit (unconscious memory)
Declarative – pertains to facts, explicit
Episodic – memory for events and order that they took place, explicit
Working – a.k.a. holding memory
Declarative and episodic are explicit, you know what you know – involves hippocampus and
parahippocampal structures
Population code
relates to population firing rate vector, e.g. primary motor cortex, measure and list firing rate of 100
neurons
firing patterns can change over time, related to experiences and/or actions
in motor cortex, population firing rate vector refers to motor cortex neuron activations that result in
pattern of muscle activations or muscle synergy
in contrast to the “grandmother cell”, which is not really true
there’s no single cell in the brain that does all the work for an action or perception
always, always, always a population of active neurons
In hippocampus, the firing of cells may be unique to particular location in space
Can figure out where the animal is in space based on population firing rate vector, this firing pattern
develops over time
population firing rate vector used as a tool to develop brain computer interfaces
Feedback properties in brain
Top-down processing (pre-frontal cortex)
akin to re-entry (hippocampus, cerebellum, basal ganglia)
and functional anatomy (neuromodulators)
one structure can project to “earlier” structures in a process and influence their activity, e.g. visual
cortex is “early” in visual processing, then activation moves to what and where pathways
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Projections from cortex, thalamus, neuromodulatory systems can influence how visual cortex processes
visual input…examples of top-down processing, re-entry, and functional anatomy
Premotor cortex
Indirect roles of premotor cortex, not necessarily directed to action in the moment, but can also be
related to actions in an indirect way,
e.g. planning of upcoming action,
observation of an action (mirror neurons),
sequence-dependent
Prefrontal cortex
Prefrontal cortex, neuron activation can reflect abstract variables of a behavioral task, such as
interval timing,
categorization of sets of episodes,
counting number of items in visual field,
marking beginning or end of episodes
Often come in form of working memory or delay activity
Cue-delay-action, PFC maintains memory during delay
cue+delay neurons
action+delay neurons
don’t need to be about explicit cues, but can be about abstract properties like beginning of time interval
Motor control
Motor neuron goes to muscles, motor cortex neuron synapses on motor neurons
Spinal cord interneurons can be either excitatory or inhibitory
One motor cortex neuron might activate one neuron to cause muscle action and activate inhibitory
interneurons to keep other muscles from contracting
coordination of several muscles can happen by virtue of interneurons
motor neurons receive converging and diverging inputs from motor cortex neurons
motor neurons only go to one muscle (can be many fibers, but only one type of fiber, i.e. slow-twitch or
fast-twitch)
ventral spinal cord interneurons, one way that the coordination of different muscles is achieved
Features of plasticity, changes in synaptic strengths
know the ways that a synapse can change, depends on co-activity patterns
Potentiation
Depression
Spike-timing dependent plasticity
can induce action potential in pre-synaptic neuron or post-synaptic neuron and record in pre- or postE.g. induce action potential in post-synaptic neuron immediately followed by pre-synaptic neuron 100+
times
Results show that the post-synaptic neuron is less likely to fire when the pre-synaptic neuron fires, this is
synaptic depression
If induce pre-synaptic neuron immediately followed by post-synaptic neuron
Result, post-synaptic neuron more likely to fire after pre-synaptic neuron, this is synaptic potentiation
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There are many spike timing dependency curves
ACh and NE can change the shape of the curve
Order of firing matters
Standard curve for cortical pyramidal and hippocampal pyramidal cells
Different for Purkinge cells of cerebellum
Related to spike timing and neuromodulators
Same general pattern with no Ach and no NE (NREM sleep) and with high ACh and NE (Waking)
ACh and no NE (REM sleep), we see synaptic depression, no potentiation (difficult to induce long-term
potentiation in hippocampus during REM sleep)
Co-activity matters, but timing doesn’t matter
ACh – more is better when learning motor or perceptual skills
Supports dedication of more brain space to that stimulus
Without ACh, learning doesn’t happen well
FYI… (not exam material)
Can boost seratonin by taking tryptophan, which is a precursor, (turkey, milk)
Choline sources – meat, cauliflower, navy beans, tofu
Action sequence activity in premotor neurons
Rat in a maze:
action mapping
action planning
sequence-dependent
Monkey drawing a shape
end of sequence
beginning of sequence
both independent of direction of motion
Labile memories
Pavlovian fear conditioning
Associative memory, if recalled later, the memory is labile.
Give drug that blocks potentiation
Present conditioned stimulus without unconditioned stimulus, association is lost immediately
Attention
pop-out or bottom-up attention — sensory system draws your attention to it
Search or top-down attention — PFC needs to keep memory of search object active so object of interest
can be found
In pop-out condition, LIP (parietal) finds the object of interest first as shown in the neuron’s firing
activity
In search condition, frontal eye fields active first, LPFC fire first, enabling LIP to identify object
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Attention as selection process, IT neuron that responds preferentially to specific visual stimulus
(flowers) will fire more when it has to attend to that stimulus (flowers)
When monkey needs to ignore that stimulus to focus on another stimulus (martini glass), the flower
neuron fires less
Implicit/procedural learning
(Study this slide from lecture)
Basal ganglia vs. hippocampus
Rat in T-maze
Does rat learn to go to a specific place or make a left turn to get the reward?
When the maze is flipped early in training (in the first 2 days), the rat will first go to the place, use place
strategy
When the maze is flipped later in training (3 days and beyond), the rat will make a left turn, use the
response strategy
If hippocampus is inactivated during first couple of days, rat won’t use place strategy, but will use
response strategy
If basal ganglia is inactivated at 3 days and beyond, rat won’t use response strategy, but will use place
strategy
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