Welcome to Biological Psychology: Regions of the Brain

Welcome! In this chapter for OCR A Level Psychology (Component 02: Psychological themes through core studies), we will explore the fascinating key theme: Regions of the Brain. Have you ever wondered if the two halves of your brain think independently, or why some people find it so easy to resist temptation while others give in immediately? By looking at two groundbreaking studies—the classic study by Sperry (1968) and the contemporary study by Casey et al. (2011)—we will discover how specific areas of our brain control our thoughts, speech, and self-control.

Don't worry if brain terminology feels a bit overwhelming at first. We will break down every experiment step-by-step with clear analogies, memory tricks, and direct tips to help you secure top marks in your exam!


Part 1: The Core Mechanism — How the Brain is Wired

Before diving into the studies, let's look at one fundamental rule of human biology: contralateral processing. "Contra" means opposite, and "lateral" means side.

• Left Hemisphere (LH): Controls the right side of the body and receives visual input from the right visual field (RVF). Crucially, for almost all right-handed people, the left hemisphere houses the language centres (speech and writing).

• Right Hemisphere (RH): Controls the left side of the body and receives visual input from the left visual field (LVF). It specialises in spatial awareness, non-verbal recognition, and drawing, but cannot speak.

• The Corpus Callosum: A thick bridge of nerve fibres that connects the two hemispheres, allowing them to share information instantly. When this bridge is cut, the two halves cannot talk to each other!

Exam Pitfall Alert: Never say "left eye" when you mean "left visual field"! Both eyes have a left visual field and a right visual field. The Left Visual Field (LVF) of both eyes sends its signals strictly to the Right Hemisphere.


Part 2: Classic Study — Sperry (1968)

Hemisphere deconnection and unity in conscious awareness (The Split-Brain Study)

1. Background and Aim:
In severe cases of epilepsy, surgeons sometimes perform a commissurotomy (cutting the corpus callosum and anterior commissure) to stop seizures from spreading from one hemisphere to the other. Sperry wanted to examine the behavioural and cognitive effects of this hemisphere deconnection and investigate the unique functions lateralised to each hemisphere.

2. Participants and Design:
• Sample: \(11\) split-brain patients who had undergone commissurotomy.
• Research Method: A quasi-experiment (the independent variable—having a split brain vs. an intact brain—was naturally occurring).

3. Apparatus and Procedure:
Sperry used a piece of equipment called a tachistoscope to present visual stimuli.

• The \(1/10\text{th}\) of a Second Rule: Images or words were flashed for exactly \(1/10\text{th}\) of a second (\(100\text{ ms}\)). Why? Because it takes longer than \(100\text{ ms}\) for the human eye to make a movement (a saccade). Flashing the image this fast ensured that only the intended visual field received the information!

• Visual Tasks: The participant focused on a central fixation point while stimuli flashed to either the Left Visual Field (LVF), Right Visual Field (RVF), or both simultaneously.

• Tactile (Touch) Tasks: Participants were blindfolded or reached beneath an opaque screen. Objects were placed in their left or right hand to test whether they could identify them without seeing them.


Key Findings of Sperry (1968)

A. Visual Presentation:
• Stimulus flashed to RVF: Information travelled to the Left Hemisphere (LH). Because the LH controls speech, the patient could easily say and write what they saw.
• Stimulus flashed to LVF: Information travelled to the Right Hemisphere (RH). Because the RH has no speech centre, the patient verbally claimed: "I saw nothing" or saw a flash of light. However, when asked to point to or pick up the object with their left hand (controlled by the RH), they could do it correctly!

B. Tactile Presentation:
• Object placed in Right Hand: Sent to the LH \(\rightarrow\) Patient could name and describe the object verbally.
• Object placed in Left Hand: Sent to the RH \(\rightarrow\) Patient could not name it verbally, but could search through a bag of objects with their left hand and retrieve the matching item.

C. Dual-Field Composite Stimulus (The "Key-Ring" Test):
When the word "$Key-Ring$" was flashed so that "$Key$" was in the LVF and "$Ring$" was in the RVF:
• The patient verbally said: "Ring" (RVF \(\rightarrow\) LH with language).
• With their left hand, the patient picked up or pointed to the Key (LVF \(\rightarrow\) RH controlling left hand).


Conclusions and Evaluation

• Conclusions: Sperry proved that the left hemisphere is dominant for language and verbal processing, whereas the right hemisphere is specialised for non-verbal, spatial, and tactile recognition. Each disconnected hemisphere possesses its own stream of conscious awareness, memory, and perception.

• Strengths: High internal validity due to extremely high standardisation (the \(100\text{ ms}\) tachistoscope presentation and central fixation point prevented eye movement confounds).

• Weaknesses: Small, atypical sample (\(11\) patients). All participants suffered from severe epilepsy and had drug treatments, meaning their brains might not represent the general population (low population validity).

Key Takeaway for Sperry: RVF \(\rightarrow\) Left Hemisphere \(\rightarrow\) Can Speak. LVF \(\rightarrow\) Right Hemisphere \(\rightarrow\) Can Point/Draw with Left Hand, but Cannot Speak!


Part 3: Contemporary Study — Casey et al. (2011)

Behavioral and neural correlates of delay of gratification 40 years later

1. Background and Aim:
In the late 1960s and early 1970s, Walter Mischel tested preschoolers using the famous "marshmallow test" to measure delay of gratification (the ability to resist an immediate reward for a better reward later). Casey et al. wanted to test whether this ability remains a stable personality trait \(40\text{ years}\) later in adulthood, and to identify the specific neural correlates (brain regions) involved in impulse control.

2. Participants and Design:
• Research Method: A longitudinal quasi-experiment tracking participants from age \(4\) into their mid-\(40\text{s}\).
• Experiment 1 (Behavioural): \(59\) participants (\(32\) High Delayers, \(27\) Low Delayers) completed impulse control tasks on laptops at home.
• Experiment 2 (Neural/fMRI): \(26\) participants (\(15\) High Delayers, \(11\) Low Delayers) completed the tasks while inside a functional Magnetic Resonance Imaging (fMRI) scanner to measure brain activation.

3. The Go/No-Go Paradigm:
Participants viewed faces flashed on a screen for \(500\text{ ms}\) with an interval of \(2\text{ to }5\text{ seconds}\). They were told to press a button when they saw a target face (Go trial) and resist pressing when they saw a non-target face (No-Go trial).

• "Cool" Task: Neutral facial expressions (e.g. Go for neutral male face, No-Go for neutral female face). This tests basic cognitive control without emotional pull.

• "Hot" Task: Emotionally alluring faces (e.g. Go for fearful face, No-Go for a smiling, happy face). Smiling faces act as social rewards and test resistance to temptation!


Key Findings of Casey et al. (2011)

A. Behavioural Results (Exp 1 & Exp 2):
• Both High and Low Delayers were highly accurate on "Go" trials across all tasks.
• Both groups performed equally well on "Cool" No-Go trials.
• The Critical Difference: Low Delayers made significantly more false alarms (errors of commission) on "Hot" No-Go trials when the non-target was an alluring happy face. They could not suppress the impulse to press the button!

B. Neural / fMRI Results (Exp 2):
The study identified two crucial brain structures forming the frontostriatal circuitry:

1. Inferior Frontal Gyrus (part of the Prefrontal Cortex / PFC):
This is the brain's "brakes" (top-down cognitive control). It showed elevated activation during successful No-Go inhibition. High Delayers showed greater recruitment of this region when resisting temptation.

2. Ventral Striatum:
This is the brain's "reward centre" (bottom-up emotional and reward drive). Low Delayers showed exaggerated hyperactivity in the ventral striatum specifically when presented with alluring ("hot" happy face) No-Go trials.


Conclusions and Evaluation

• Conclusions: Delay of gratification is a stable individual difference trait over \(40\text{ years}\). Resistance to temptation relies on frontostriatal circuitry: top-down cognitive control by the prefrontal cortex (inferior frontal gyrus) suppresses the bottom-up, reward-seeking impulses of the ventral striatum.

• Strengths: Highly objective, scientific data using fMRI scanners and standardized timings (\(500\text{ ms}\)); impressive longitudinal tracking over \(40\text{ years}\).

• Weaknesses: High sample attrition (drop-out rate) over \(40\text{ years}\). The original cohort was drawn from Stanford Bing Nursery School, making the original sample socially unrepresentative.

Exam Pitfall Alert: Do NOT say low delayers were worse at all tasks! They were perfectly fine at pressing "Go" and fine on neutral "Cool" tasks. Their difficulty was only when trying to stop themselves on alluring, happy "Hot" No-Go cues.

Key Takeaway for Casey et al.: High Delayers use their Prefrontal Cortex (Inferior Frontal Gyrus) to hit the brakes. Low Delayers have an overactive Ventral Striatum (Reward Centre) when faced with tempting cues.


In Section A of Component 02, OCR frequently asks you to explain how the contemporary study (Casey et al.) changes, extends, or confirms the classic study (Sperry) in relation to the key theme: Regions of the Brain.

1. Progression in Technology:
• Sperry: Relied on natural surgical lesions (commissurotomy) and a basic visual apparatus (tachistoscope) to infer brain function.
• Casey et al.: Used modern, non-invasive, high-precision neuroimaging (fMRI) to view real-time blood flow and active neural firing in living, healthy brains.

2. Macroscopic Lateralisation to Microscopic Functional Circuits:
• Sperry: Looked broadly at the macro-level differences between the two hemispheres (Left Hemisphere = language; Right Hemisphere = spatial/non-verbal).
• Casey et al.: Extended this to specific, localised subcortical and cortical circuits (frontostriatal circuitry: Inferior Frontal Gyrus vs. Ventral Striatum) and how they interact to regulate self-control.

3. Atypical vs. Typical Populations:
• Sperry: Studied a very small, clinical group of \(11\) severe epileptics whose brains had undergone major surgery.
• Casey et al.: Studied typical, healthy individuals across their normal developmental lifespan from age \(4\) to \(44\).


Part 5: Quick Revision Check

Use these rapid checks before your exam to ensure you have mastered the core facts:

• Sperry Tachistoscope Time: \(1/10\text{th}\) of a second (\(100\text{ ms}\)) \(\rightarrow\) Prevents eye saccades.

• Sperry RVF vs LVF: RVF goes to Left Hemisphere (can speak/write); LVF goes to Right Hemisphere (can point with left hand, cannot speak).

• Casey Stimulus Time: \(500\text{ ms}\) presentation (\(2\text{ to }5\text{ s}\) jittered inter-trial interval).

• Casey Brain Regions: Inferior Frontal Gyrus = Self-control / inhibition (High Delayers). Ventral Striatum = Reward / temptation (Low Delayers).

• Core Theme Connection: Both studies show that distinct regions of the brain perform specialised cognitive functions, moving from hemisphere lateralisation (Sperry) to frontostriatal network balance (Casey et al.).