Interference

Methods Overview:

  • How does the brain give rise to behavior?

  • We have sensory neurons, motor neurons, and lots more in between

  • To figure out what the in between neurons do we can inc and dec function to see what contributes to neural activity

  • Look for correlations between function and structure and behavior

  • These are called interferences

  • Will go through 4 diff methods and if they’re invasive, dec/inc neural activity



Lesions

  • Causes of legions in the brain include injury, surgery, stroke, hemorrhage, tumor, congenital, degenerative disease

  • In animals they used to take out parts of cortex to see what animals still could/nt do



Early Ideas

  • It was thought that behavior was linked to soul mostly

  • Paul Broca found patient that could only say tan

  • He had a lesion caused by syphilis in left IFG, now known as broca's area

  • Earliest example of brain area and function

  • Phineas gage: tamping iron rod went through his brain and eye while he was working railroad; went through left frontal lobe of cortex, left and right orbital cortex

  • After initial fall, he was unconscious and communicative and pretty normal, then his behavior was different

  • He became fitful irreverent impatient stubborn, etc. he was “no longer gage”

  • Evidence that brain injury can change personality

  • Limbic network and orbitofrontal cortex is affected bc they control emotions and stuff

  • Default mode network affected his social cues and planning



Henry Molaison

  • Developed anterograde amnesia after surgery

  • He had severe epilepsy they thought was coming from the hippocampi so they removed both

  • He couldn't form new memories

  • He could learn motor tasks from the cerebellum and basal ganglia but not memories that are encoded in the hippocampus

  • Study his brain and how its different, the missing hippocampus, large ventricles, corpus callosum is thinned, cortex is thin, caudate looks different; damage in media orbitall frontal perhaps bc of brain connections



Group Studies

  • In modern neuroscience, findings are made typically in these 2 ways:

  • 1. Group ppl by behavioral symptom ie. can’t talk or can't make memory or can’t control emotions and urges

  • 2. Group by lesion location ie.if orbital frontal cortex is in charge of emotion regulation, do those w/o it having trouble w emotional regulation?

  • Example: in a study participants either couldn't talk or couldn't understand; they used an mri to look for overlap; the graph shows what percentage of damage the participants/patients had; the IFG/broca's area is affected in all patients w production deficits; pattern of damage is more diffuse in patients w comprehension deficits w most overlap in posterior areas, which we know is wernicke’s area 


  • Another example is cigarette smokers quitting after having a brain injury showing links to the insula part of brain and addiction

  • exam questiondeisgn a study:how would you figure out what a brain region does by studying patients with lesions to that area?



Electrical Stimulation

  • Electrodes are inserted in brain to cause or stop neuronal firing

  • Invasive, done during neurosurgery

  • Done to figure out which part of the brain received sensory input or controlled motor output 

  • electrode in motor homunculus would cause that body part to move ie. the thumb moving when electrode inserted in that area; sensory homunculus electrode feel like for example thumb being brushed

  • While someone is undergoing surgery you can stimulate that part of the brain (stop neuronal functioning) to see if it affects certain functions; done most commonly w language

  • Can be done to inc and dec activity but its invasive



Optogenetics

  • Mostly done in mice, some rats too

  • Control neurons by turning them on and off with light

  • You create a genetic construct of light sensitive ion channels for neurons with these certain protein, insert it in a virus, put the virus in the mouse brain,fiber optic cable implanted in brain, lasers of specific wavelengths are imputed in the animal; this is precise and target a specific kind of neuron with the light whereas in 8nn electrical stimulation its not as precise

  • Using light to target specific neuron types; turn on or off the amygdala for example and seeing how it changes behavior



Transcanial Magnetic Stimulation

  • A figure 8 shaped coil creates a magnetic field which disturbs the electrical flow of neurons



  • Positive charges down towards the cell body can depolarize neurons and lead to excitation

  • TMS can excite or inhibit neurons near the edge of cortex

  • Helps us map brain and motor functions

  • Has been FDA approved for migraines, depression, OCD

  • Pros: Temporary, focal, can be randomly assigned

  • Cons: some areas can’t be stimulated ie. amygdala, hippocampus, basak ganglia, etc. the stuff that is in the medial surface/the stuff not on the outer surface; we dont know the size of how much cortex is breing stimulated, sometimes you dont know which neurons are excitatory or inhibitory and how/where to access threm