Maguire

Background

What is the Limbic system + Hippocampus

• Limbic system is a part of the brain responsible for emotional response and long term memory
  
  
• Hippocampus is part of the limbic system, responsible for long term memory and spatial navigation. 

Maguire

Aim

• To determine whetther changes could be detected in the brains of humans who have extreme experience in spatial navigation. This change would be found in the Hippocampus.

Maguire

Sample

• 16 male right handed taxi drivers (the london black cabs) who had all completed 'the knowledge' exam. 
   
• All aged between 32 and 62 with a mean age of 44.
  
  
• Range of taxi experience was from 18 months to 42 years with an average of 14.3 years.
  
  
• All had healthy medical, neurological and psychiatric profiles.
  
  
• Compared to 50 age matched right handed male MRI scans taken from the database of the center where MRIs for the study conducted.
  
  
• Control group age range from 32 to 62 and spread of ages + mean age were similar to match the cab drivers.
  None of the control group were cab drivers. 

Maguire

Method

Techniques used for analysis?

• MRI gives 2D image of the brain.
  
  
• Voxel based morphology and Pixel counting used to analyse the overall volume of the brain in 3D.
  
  Voxel = a 3D pixel 

Maguire

Results

Overall size, Posterior vs Anterior volume

Right posterior correlation

• No overall hippocampal volume difference between cab drivers and controls.
  
  
• Cab drivers had larger posterior hippocampi than controls. controls had larger anterior hippocampi than the cab drivers
  
  
• The longer a cab driver had been working, the greater the size of his right posterior hippocampi, the smaller the size of his anterior hippocampus

Maguire

Conclusions

Experience as cab driver = ???

Predisposition

Changes due to experience

Tissue migration

• Results could be explained by a larger posterior hippocampal volume giving the driver a predisposition to work involving spatial navigation.
  
  
• However, the more experience a cab driver has, the greater the size of his posterior hippocampus, suggesting a change in posterior hippocampal volume over time and with use.
  
  
• Tissue seemingly migrates from the anterior to the posterior brain when these changes occur, an example of the brain's plasticity, not new tissue growth. 

Dement & Kleitman

Background

REM and NREM sleep

• It was hypothesised that people dream during REM sleep, as stage of deep sleep entered for 10-15 minutes every 70-90 minutes of sleep. EEG traces show brain activity that is near that of someone that is awake during REM sleep.
  
  
• People were not thought to dream during NREM sleep, the brain is less active during these times.

Dement & Kleitman

Aim + Research Questions

• To investigate whether dreaming can be correlated with physical phenomenon.
  
  
• RQs
  
  1- Will be more likely to report dreams if they are woken during REM sleep rather than NREM sleep?
  
  2- Can people accurately estimate the duration of dreaming?
  
  3- Is the direction of REM related to dream content? 

Dement & Kleitman

Sample

• Seven adult male + 2 adult females
  
  
• 5 studied intensively
  
  
• the other 4 used to confirm results, minimal information recorded. 

Dement & Kleitman

Method

• Lab experiment
  
  
• Takes place in a sleep laboratory, participants would travel here just before their normal bedtime.
  
  
• Asked not to consume alcohol or caffiene during the study.
  
  
• Electrodes attatched to the heads of participants as they slept, electrodes attatched the a continuously running EEG
  
  
• At various times in the night participants were woken by the sound of a doorbell and were asked to record the content of any dreams in the tape recorder near their bed.

Dement & Kleitman

Results

The answers to the 3 research questions

• Q1 - 
  
  All subjects displayed REM, eye movement not constant, in bursts of 2 - 100 movements. REM occured at regular intervals
  
  351 awakenings, either randomly or for 1 person in a 3REM/3NREM pattern, one person woekn randomly but told he would only be woken during REM :L
  
  Woken during REM = 151 recalled dreams / 39 no recall
  
  Woken during NREM = 11 recalled dreams / 149 no recall
  
  No differences were seen in the misled or patterned awakening participants.
  
  
• Q2-
  
  Participants woken after either 5 or 15 minutes of REM, asked whether dreaming for 5 or 15 minutes.
  
  Woken at 5 --> 45 correct / 6 incorrect 
  
  Woken at 15 --> 47 correct / 13 incorrect
  
  Mostly accurate in estimation, one participant was useless, responsible for a large number of errors.
  
  
• Q3-
  
  Participants woken after a period of eye movement of a specific type persisted for more than 1 minute
  
  35 of these awakenings, asked to describe dream content, placing of electrodes determined REM direction.
  
  Mainly vertical REM - observed 3 times
  eg. Throwing basketballs at a net 
  
  Mainly horizontal - observed 1 time
  eg. Watching 2 people throw tomatoes at each other
  
  Both V + H REM - observed 21 times
  eg. Fighting with someone / Looking at things
  
  Little to no REM - observed 10 times
  eg. Staring at an object / Driving a car 

• They were all correct / supported by the observations. Simples.

• A callosectomy procedure severs the corpus callosum, the bridge between the two frontal lobes of the brain, through which they communicate.
  
  
• Severing this was done in response to severe epilepsy, the thinking went that if the electrical discharge that causes an epileptic fit can be contained to one half of the brain, the fit would be less severe.
  
  
• It was recognised that patients that underwent these procedures were useful in the study of hemispheric specificity. 

Sperry

Aim

• Attempt to understand the functions of the seperated hemispheres

Sperry

Sample

details of two patients

• 11 participants, all with severed corpus callosums
  
  Two patients described in detail. 
  
  One a man who had been having high risk of death seizures twice a week for 10 years, since having surgery, no seizures and significant reduction in medication.
  
  Next, a 30 something woman, described as seizure free since the procedure 4 years ago, also reported to have a normal EEG trace.

Sperry

Method

The apparatus, visual tasks and tactile tasks

• For visual tasks, participants had their visual fields bisected, two screens that transmitted images into only one visual field were set up, one eye was covered, to prevent any info entering that visual field.
  
  Participants had one eye covered and would fixate on a central point between the two screens. Images were flashed into either visual field for less than 1/10th of a second, enough for the brain to regester, but not fast enough for the eyes to move in response to the stimulus, therfore ensuring only 1 visual field recieved the image. 
  
  
• For tactile tasks, objects hands screened from view, participants were instructed to handle various objects or do various tasks with different hands. 

Sperry

Findings

Findings that show hemispheric independence
1-5

• Information in one visual field not seen by the other is only registered by the corresponding hemisphere, the other hemisphere has no knowledge of the image whatsoever.
  
  
• Visual material shown to the RVF and concequently, the LH can be described in speech and writing.
  
  If the same is shown to the LVF/RH the participant insists they did not see anything, however, if you ask the participant to point to the object he just saw with his left hand, he can pick it out of a large selection of objects.
  
  
• Now the tricky one.
  
  dollar sign shown to LVF/RH
  question mark in the RVF/LH
  
  ask the participant to draw what he has just seen with his left hand/RH, he will of course draw the RH dollar sign
  
  Ask him what he has just drawn?
  
  He will tell you he has drawn the question mark seen in the RVF/LH.
  
  As only the LH can speak, this has to be his answer, both hemispheres are unaware of the others activity.
  
  
• Objects put in the right hand /LH can be described and named.
  Objects in left hand /RH, participant makes wild guesses or maybe unaware of objects presence, can still point to that object later (out of a collection of objects) with the left hand. 
  
  
• If two objects are given, one to each hand and then put in a bag and searched for by both hands, one hand will reject the one the other is looking for while searching, as if two seperate people were working at the task. 

Sperry

Findings 2

Right hemisphere function

6-11

• Select similar items to a known target item (eg. a watch rather than a clock)
  
  
• Perform simple arithmetic
  
  
• Understand both written and spoken words, however cannot itself write or verbalise.
  
  
• Identify objects with the left hand. eg. If asked to select some cutlery from a selection of objects, can select a fork. If then asked what was selected, the participant may well answer spoon or knife, as the LH doesn't know what has been selected, so guesses at random.
  
  
• Understand complex instruction eg. Find something to clean dirt with = soap / Find something to insert into a slot machine = coin
  
  
• Show appropriate emotional reaction. eg, A nude picture is flashed into the LVF, the participant denies seeing anything, but may blush or giggle, suggesting the picture was registered at an emotional level.