Social Brain Hypothesis

These flashcards encapsulate the key vocabulary and concepts related to the Social Brain Hypothesis as discussed in the lecture.

Social Brain Hypothesis (The Computational Demand)

A theory proposing that the primary evolutionary pressure for the increase in primate brain size was the complexity of social environments. Unlike the Ecological Brain Hypothesis, which focuses on foraging efficiency, this hypothesis suggests that managing coalitions, navigating hierarchies, and social manipulation requires significant neocortical expansion.

Neocortical Ratio (The Index of Complexity)

The ratio of the volume of the neocortex to the volume of the rest of the brain. Because the neocortex is responsible for higher-order cognitive functions, a higher R_n is strongly correlated with larger social group sizes in non-human primates, serving as a proxy for social processing power (R_n = \frac{V{neocortex}}{V{total} - V_{neocortex}}).

Dunbar's Number and Cognitive Constraints

A theoretical limit of approximately 150 individuals for maintainable social relationships. This number is based on the correlation between brain size and social group size; it suggests that human social cohesion is limited by the capacity of the neocortex to track and process multi-level social information.

Prosopagnosia: Dissociating Identity and Expression

A selective deficit in face recognition where patients cannot identify familiar faces but may still recognize emotions, gender, or age. This suggests that the neural pathways for identity (ventral stream) are functionally distinct from the pathways for processing changeable social cues.

Fusiform Face Area (FFA) and Configural Processing

Located in the lateral fusiform gyrus, the FFA is central to 'holistic' or configural processing, where faces are recognized as a single gestalt rather than a collection of parts. Damage here leads to impaired identity recognition while leaving object recognition relatively intact.

The Haxby Model: Core vs. Extended Systems

A model partitioning face processing into the Core System (OFA, FFA, STS), which extracts visual features, and the Extended System (Amygdala, Insula, mPFC), which processes the emotional, linguistic, and biographic significance of the face.

Occipital Face Area (OFA) Functionality

Considered the first stage of the face-processing network, the OFA is responsible for processing individual facial components (eyes, nose, mouth) before sending this information to the FFA for holistic integration.

Superior Temporal Sulcus (STS) and Changeable Aspects

A region that processes dynamic social cues, such as eye gaze, facial movements, and lip-reading. It distinguishes itself from the FFA by its sensitivity to biological motion and its role in interpreting the intentions of others based on visual movement.

Amygdala and Social Threat Detection

A subcortical structure critical for the rapid detection of social threats. It shows heightened activity in response to fearful facial expressions and eye gaze directed toward a potential environmental threat, facilitating an immediate 'fight or flight' response via the hypothalamus.

Biological Motion and Point-Light Displays

The ability to perceive the form and movement of a living being from minimal kinetic cues (e.g., lights attached to joints). This processing occurs largely in the STS and is crucial for detecting animacy and predicting the trajectory of social agents.

Multi-modal Integration in the STS

The STS is not strictly visual; it integrates information from multiple senses. For example, it shows increased activation when the visual movement of lips matches a vocalization, providing the neural basis for the McGurk effect and better speech comprehension in noise.

Action Potential: The All-or-None Principle

The fundamental unit of neural communication. It occurs when a neuron's membrane potential reaches a threshold (approx. -55\ mV), causing voltage-gated Na^+ channels to open, resulting in rapid depolarization. The signal is self-propagating and does not diminish in strength as it travels down the axon.

Resting Membrane Potential Dynamics

The electrical gradient of a neuron at rest, typically -70\ mV. This state is maintained by the Sodium-Potassium pump (3\ Na^+ out/2\ K^+ in) and the selective permeability of the membrane to K^+ ions through leak channels.

Skin Conductance Response (SCR) and Covert Recognition

A measure of sympathetic nervous system activity. Even in patients with prosopagnosia who cannot consciously identify a face, a significant increase in SCR is often observed for familiar faces, indicating that subcortical emotional recognition remains intact despite a lack of conscious identification.

Capgras Syndrome: The Inverse of Prosopagnosia

A delusion where a person believes familiar people have been replaced by imposters. Neurally, this is interpreted as the opposite of prosopagnosia: conscious face recognition is intact, but the emotional 'glow' (measured by SCR) is missing, leading the brain to rationalize the lack of emotional response as the person being a fake.

Electromyography (EMG) in Social Mimicry

A technique used to detect tiny muscular movements. In social cognition, it reveals 'facial mimicry'—the automatic, unconscious imitation of another's facial expression, which is thought to facilitate empathy and emotional contagion.

Eye Gaze Processing and Joint Attention

The ability to track another individual's direction of gaze to attend to the same object. This is a foundational social skill mediated by the STS; failure to develop this is a hallmark of certain social communication disorders.

Ecological Brain Hypothesis (The Alternative View)

Proposes that brain expansion was driven by the need to solve environmental problems, such as remembering the location of ephemeral fruit sources or developing complex extractive foraging techniques, rather than social dynamics.

Ventral vs. Dorsal Streams in Face Processing

The Ventral stream (involving the FFA) focuses on 'Who is it?' (identity recognition), while the Dorsal stream/Superior temporal regions focus on 'What are they doing?' (expression, gaze, and movement).

The Thatcher Illusion and Inversion Effect

An effect where it is difficult to detect local feature changes (like upside-down eyes) in an inverted face, but easy when the face is upright. This demonstrates that face processing is uniquely dependent on upright holistic configuration rather than individual feature analysis.

Simulation Theory vs. Theory-Theory

Two models for how we understand other minds. Simulation Theory suggests we use our own neural circuits (like mirror neurons) to 'simulate' others' states, while Theory-Theory suggests we store a library of 'rules' and abstract knowledge about how people behave.

Mirror Neurons and Action Understanding

Neurons, originally found in the premotor cortex and inferior parietal lobule, that fire both when performing an action and when observing another perform the same action. They are hypothesized to provide a direct neural bridge for understanding the intentions behind physical movements.

The Right Hemisphere Dominance in Faces

Face recognition is typically lateralized to the right hemisphere. Damage to the right fusiform gyrus is more likely to result in permanent prosopagnosia than damage to the left, which is more often associated with word and object recognition.

Oxytocin and Social Bonding

A neuropeptide synthesized in the hypothalamus and released by the posterior pituitary. It modulates social behaviors like trust, pair-bonding, and maternal care by reducing amygdala reactivity to social stressors and enhancing the reward value of social interactions.

Temporal Pole and Social Knowledge

A region involved in the storage of biographical social knowledge. It acts as a semantic hub that links a face (from the FFA) or a voice with specific personal information and memories about that individual.