Explanation​:
Research on depression suggests that heritability of depression is a result of both genetic and environmental factors (Caspi et al., 2003). Genetic factors contribute to individual differences in depression, and environmental factors contribute.

Explanation​:
The primary role of GABA (gamma-aminobutyric acid) is to send inhibitory signalling to the brain and reduce the effect of the excitatory neurotransmitter. It promotes relaxation by inhibiting the neurons from firing and balancing brain activity.

Explanation​:

The modern theory of evolution is based on the following premise:

• organisms are driven by the need to survive and reproduce
• organisms having different traits are adapted to their environment to varying degrees, or what is called differential fitness
• organisms that adapt well to environmental changes have a higher chance of survival

Explanation​:
Serotonin is a neurotransmitter responsible for regulating essential bodily functions, including mood, sleep, and learning and memory processes. It acts as a chemical messenger and passes messages from the brain to the rest of the body. Serotonin deficiency can result in depressive symptoms and anxiety in people.

Explanation​:
The ability of the brain to change throughout life is called neuroplasticity. These changes result from the formation and disruption of the synaptic connections between neurons. As a result, the neural networks in the brain change their form. These changes can happen due to brain damage or injury and learning.

Explanation​:
Phenotype is the set of traits that manifest in an individual's body, appearance, or behaviour. The set of traits as coded in an individual's DNA is called a genotype.

Phenotype comprises observable characteristics (eye colour, height) and unobservable characteristics (blood type, immune system). Genotype is the plan, and phenotype is the implementation of the plan.

Explanation​:

Choice A is correct because fraternal twins only share 50% of their genes, and identical twins share 100%. Due to this, researchers can study the differences and similarities in personality, intellect, and behaviour.

Choices B, C, and D are incorrect because they do not address the nature aspect of the nature vs. nurture debate in twin studies.

Explanation​:
The limbic system is an older subcortical structure of the brain. It is commonly called the “emotional brain” and includes several parts like the thalamus, hypothalamus, amygdala, and hippocampus. It is located on both sides of the thalamus, beneath the medial temporal lobe of the cerebrum.

It supports various functions such as emotion, behaviour and long-term memory.

Additionally, the amygdala, together with the hippocampus, are both involved in emotion and cognition as they are central to processing emotion in relation to cognitive processes such as memory.

Explanation​:
The nervous system comprises neurons consisting of soma, dendrites, and axons. A synapse or synaptic gap is the space between two neurons. An action potential is a process in which one neuron sends a message to the other neurons through an axon. An action potential is an all-or-none phenomenon. When it reaches the end of the axon, a neurotransmitter is released in the synaptic gap from the axon terminals.

Explanation​:
Leptin is a hormone that travels from the fat cells to the brain indicating that enough food has been consumed and energy burning can happen at a normal rate.

When an individual is suffering from obesity, their bodies become resistant and no longer receive the message that their body has had enough food.

The results showed that oxytocin was linked to in-group trust and cooperation, and aggression towards the members of the out-group.

Explanation​:
Synaptogenesis is an explosion of synaptic formation between neurons during early brain development. The brain experiences a lot of growth during infancy. This period of synaptogenesis plays an essential role in learning, memory formation. Active synapses are strengthened, and less active synapses are weakened. The process of removing the irrelevant/pruned synapses is referred to as synaptic pruning.

Explanation​:
The 5-HTT or serotonin receptors are found in the central or peripheral nervous system. 5-HTT stands for 5-hydroxytryptamine. Serotonin receptors affect many processes, such as memory, sleep, appetite, aggression, and anxiety. A study done by Caspi et al. in the year 2003 shows depression was also linked to a particular gene—the serotonin transporter gene 5-HTT.

Explanation​:
Vasopressin has been found to play a role in stable, long-term pair bonding in prairie voles. Prairie voles are rodents who actively select mates, are monogamous, share parenting and are characterised by long-term pair bonds.

These social characteristics found in them, along with similar brain structures and neurochemical make-up, make them a perfect sample to study social behaviour in humans.

Explanation​:
Broca's aphasia is characterized by a loss of articulated speech and a lack of understanding of grammatical structure. A person suffering from Broca's aphasia faces difficulty forming complete sentences and tends to repeat specific words while speaking. Damage to the frontal lobe can result in this kind of aphasia. The earliest discovery in this field was made by Paul Broca in the year 1861.

Explanation​:
Mammals have a separate structure responsible for pheromonal processing called the vomeronasal organ (VNO). It is located in the anterior nasal cavity. Nerves from the VNO in animal brains connect to a particular region called the accessory olfactory bulb. This region is separate from the main olfactory bulb.

Explanation​:
Hormones are chemical messengers released directly into the bloodstream by endocrine glands: adrenal glands, hypothalamus, pineal gland, pituitary gland, thyroid, parathyroid, thymus, pancreas, testes, and ovaries. These form the endocrine system.

Oxytocin is responsible for social bonding, affects trust in interpersonal interactions, and is referred to as the $\text{‘}$bonding hormone$\text{’}$ and $\text{‘}$love hormone$\text{’}$. It also helps to establish a strong bond between a mother and a child.

Explanation​:
Cortical remapping, or cortical reorganization, is the ability of one part of the brain area to assume the functions of another part of the brain in case of an injury.

Cortical remapping is explained in the research by Merzenich et al. (1984) on eight adult owl monkeys. The middle finger of the monkey was amputated, and remapping was observed in 62 days. Adjacent areas from other fingers spread and occupied the parts of the unused area / amputated area.

Explanation​:

Answer C is correct because the study mainly focused on the heritability of intelligence and the influence of upbringing.

Answers A, B, and D are incorrect because the study did not specifically focus on birth order, cultural factors, or physical health outcomes.

Explanation​:
Antagonists counteract neurotransmitters and prevent a signal from being passed further. It decreases the activation of a synaptic receptor by blocking the neurotransmitters from binding/bonding. An example of an antagonist is scopolamine, which affects the neurotransmitter Acetylcholine (ACh).

Explanation​:

In neurological diseases, axons can regenerate or sprout in an attempt to reconnect with the target neuron and restore synapse function.

A is for synaptic plasticity, C is for synaptic pruning and D is about cortical remapping

Explanation​:

A, B and D are functions of the MRI and fMRI.

The difference between the MRI and fMRI is C, the ability to produce a video representation of brain activity over time, which a normal MRI cannot do.

MRI scans use magnetic fields and radio waves to produce 3D computer-generated images.

Explanation​:
Twin studies are small in sample size and rare due to the uniqueness of their target group. It becomes difficult to collect samples depending on the aim of the research. Twin studies are on monozygotic or dizygotic twins or both. This results in issues with the replication of similar studies.

Options A, B and C are strengths of twin studies.

Explanation​:
EEG - Electroencephalography measures the electric potentials generated by the neural circuits; neurons here interact with each other by sending electrical impulses. In this method, electrodes are attached to the scalp and pick up the changes in the electric potential of the scalp areas. EEG has a perfect temporal resolution and can detect changes in brain activity within milliseconds. Because of this, it outperforms techniques such as fMRI.