Core Studies - Physiological Approach

Background: Previous research confirmed the hippocampus plays an important role in facilitating memory in the form of navigation. The hippocampus is a part of the forebrain located in the medial temporal lobe. It plays major roles in short term memory and spatial navigation. Taxi drivers in London must undergo extensive training which takes around 2 years to acquire.

Aim: To find out whether those who rely on spatial navigational skills have structural changes in their brain, especially the hippocampus. It's assumed the hippocampus has plasticity so the volume of grey matter can change in response to learning and experience.

Hypothesis: The hippocampus in London Taxi drivers will be structurally different to the hippocampus in non-taxi drivers.

Method: Quasi-experiment; IV = amount of navigational skills used in day to day life (i.e. taxi driver or non-taxi driver); DV = Structure and volume of grey matter within the hippocampus.

Using 16 black cab drivers from London who were: Right-handed, Male, Average age 44, age range 32-62, licensed more than 18 months. Also using 50 non-taxi drivers chosen from structural MRI scan database where the taxi drivers were scanned and matched with the experimental group: Right-handed, Male, Average age 44, Age range 32-62.

Procedure: MRI scans of the 50 non-taxi drivers were analysed to establish a comparison database of average hippocampi. The brains of taxi-drivers were also scanned and compared to the database. Grey matter contains neural cell bodies.
          Data was analysed through 'Voxel Based Morphology' and 'Pixel Counting'. VBM was used to measure the density of grey matter in the brain. Pixel counting was used on the scans of 16 taxi drivers and 16 age-matched controls taken from the 50 non-taxi drivers. It consists of counting pixels in images provided by MRI scans. Carried out by blind, naive researchers. 

Results: VBM analysis showed significantly greater volume of grey matter in left and right hippocampi of taxi drivers compared to non-taxi drivers. No other differences observed. Increased matter was focal and limited to posterior hippocampus. However, controls showed relatively greater volume of grey matter in anterior.

Pixel Counting analysis showed overall hippocampus volumes did not differ significantly between the two groups but anterior hippocampi volume was greater for the control compared to taxi drivers. Taxi drivers had a significantly greater posterior hippocampal volume than the control.

Correlations between VBM and amount of time spent as a taxi driver showed a positive correlation in only one brain region. As length of time as a taxi driver increased, volume of grey matter also increased.

Background: Stage 1 sleep: lowered heart rate, muscle tension and body temperature. Very similar to states of deep relaxation and hypnosis. EEG recordings showed a-waves (8-12 Hz/s). People woken easily.

Stage 2: slower and larger EEG waves (with sleep spindles - bursts of high frequency 12-16 Hz/s). Deeper than stage 1 but still woken easily.

Stage 3: d-waves (large, slow waves, 1-3 Hz/s). People don't easily respond to stimuli and quite difficult to wake.

Stage 4: d-waves (1 Hz/s). Deepest sleep; metabolic activity is low and people are difficult to wake, apart from with crying babies, etc.

REM sleep: Hardest stage to wake from, deepest sleep and rapid eye movements can be observed under closed eyelids. Brain shows EEG pattern is similar to that of being awake. 10-15 minutes in REM. Stimulates protein synthesis which replenishes worn out brain processes.

Aim: To investigate in more detail the relationship between the physiological aspects of REM sleep and the subjective experiences of dreaming. To find out: 
- If more dreaming occurs during REM sleep than non-REM sleep;
- If the length of time spent in REM sleep is related to peoples reports about how long they have been dreaming.
- If there is a relationship between the pattern of rapid eye movements and the content of the dream which people report when they woke up.

Method: 2 adult females and 7 adult males were studied over 5 studies (4 p's studied less intensively). Observation in laboratory conditions. Subjects slept in a quiet lab in the dark after their ordinary day, without consuming alcohol/caffeine.
        Electrodes placed near eyes to measure eye movement and on scalp to measure patterns of electrical activity in brain via EEG. Subjects were woken several times by doorbell noise, and had to immediately record whether they'd been dreaming and the content of the dream into a tape recorder by the bed. 

Subjects not told if their eyes had been moving while asleep. Reports of dreaming only counted if reasonably detailed and coherent dream recorded. Subjects usually went back to sleep within minutes. Woken on average 5.7 times/night.

Procedure: Study One - Subjects woken in 1 of 4 ways during either REM/non-REM sleep. 4 woken at randomly selected times and intervals; 1 woken during 3 REM sleep periods followed by 3 non-REM; 1 woken at random times but told he'd been woken during REM; 1 woken at whim of experimenter.

Study Two - Subjects woken either 5/15 minutes after REM begun. Asked to decide whether duration of their dream was closer to 5 or 15 minutes. Length of dream (measured in terms of number of words in narratives of dreams) was compared with actual amount of time they'd been in REM sleep.

Study Three - Subjects woken as soon as 1 of 4 patterns of eye movements had occurred for 1 min, and asked what theyd dreamt. Patterns of eye movements were: - mainly vertical; - horizontal; - both; - little/no eye movement.

Results: Overall, REM sleep clearly observed in every subject every night. Periods of REM tended to last longer later in night and varied between 3 and 50 mins. 
          Study One  - Significantly more dreams reported in REM than non-REM, regardless of how subjects were woken. When subjects didnt recall dreams from REM this was normally early. When subjects recalled dreams from non-REM it was often within 8 min after end of period of REM. 
          Study Two - Subjects correctly matched duration of dreams to length of time in REM. For 5-min periods, 45/51 estimates correct. For 15-min, 47/60 estimates correct. All subjects showed a significantly positive correlation between length of dream narratives and duration of REM.
          Study Three - Patterns of eye movements and content of dreams strongly associated: - 3 periods with vertical em's linked with dreams of looking up and down at cliff face, ladders, nets; - During horizontal, one subject dreamt about 2 people throwing tomatoes at eachother; 21 periods of both associated with dreaming about looking at close objects; - 10 periods of little REM linked with dreaming about looking at distant/fixed objects.

Conclusions:

 As predicted, Dement and Kleitman found:

- High incidence of dream recall obtained from participants when woken during REM, only low incidence when woken at other times (indicates dreaming occurs during REM)

- Subjects could correctly identify length of time they'd been dreaming;

- Patterns of eye movements related to visual imagery of the dream.

Background: Left hemisphere receives information from right visual field and controls right side of body (also controls ability to speak, understand language and reason things out). Right hemisphere receives information from left visual field and controls left side of body (also tasks such as drawing, spatial awareness and inuitive tasks)
                Ornstein (1986), the cerebreal cortex appeared 50m years ago. A feature in all primates is its division into hemispheres, but only in the human brain are the hemispheres specialised for different functions. Researchers noticed if patients of epilepsy had suffered damage to corpus callosum, the frequency and severity of epileptic seizures was reduced.

Aim: To find out what cognitive functions take place in each of the separate hemispheres and to investigate the behavioural, neurological effects of this surgical procedure on all direct cross-talk between hemispheres. 

Method: Quasi experiment (IV = presence or absence of brain surgery) (DV = subjects performance on variety of tasks). 11 Participants with previously undergone surgery, 9 had done surgery shortly before and 2 a long time before. No changes in intelligence or personality.

Procedure: Vision test - Participants had one eye covered and focused on designated fixation point on upright translucent screen. Visual stimuli back-projected at 0.1s (too fast for eye movements to move stimulus into wrong half of visual field). Everything seen to the left of central fixation point with either eye are projected to right hemisphere.

              Tactile test - Participants asked to feel an object behind a screen and asked to find it again in a grab bag with either the same/different hand. Participants also given 2 objects, one in each hand and then asked to search for these objects amongst a group of others. 

Results: If the visual fields are split and information is sent to only one, an image is only recognised if it is seen again by the same visual field. When visual material was projected to the right half of the field (left hemi), participants could describe what theyd seen in speech and writing but when the same material was projected to the left visual field (right hemi), participants insisted they hadnt seen anything. However, if asked to use their left hand to point to a matching picture or object from a lineup they could choose the correct item correctly.

If 2 different figures flashed simultaneously to both visual fields (e.g $ on left and ? on right) and then asked to draw what they'd seen with their left hand (out of sight), they would draw what was on the left ($) and if asked what they'd drawn they would say the image on the right (?).

       If 2 related words are simultaneously presented to the different visual fields (e.g. 'key' on left and 'case' on right), the left hand will select a key from amongst a variety of objects, whereas the right hand will write what it saw in the right visual field (case) without influence from the word in the left visual field. 

When an object was placed in their right hand for identification by touch, participants readily described it or named the object in speech or writing but when the same object was placed in the left hand they often made wild guesses and seemed unaware that there was anything there. However, if the object was taken from their hand and placed in a grab bag, they could easily retreive it using their left hand.

If 2 objects were placed in the participants hands (one in each) and then scrambled in a pile of other items, the participant would look for the objects that were in each hand but each hand would reject the item the other hand was searching for.

Conclusions: Split-brain patients fail at cross-retrieval and so the second hemisphere doesn't know what the first hemisphere is doing. Split-brain patients behave in many ways as if they have 2 independent streams of conscious awareness.