Philosophy of Mind and Cognitive Processes

Philosophical Views on Mind and Body

• Dualism: Proposes the mind and body are separate substances. The mind (non-physical) influences the body.
• Interaction Problem: A challenge for dualism: how do these distinct substances interact?
• Materialism (Monism): Argues only physical matter exists. Mental phenomena are emergent properties of the brain.
• Neuroscience: Generally aligns with materialist views, emphasizing the brain's role in mental states.

Relationship Between Tasks and Cognitive Processes

• Tasks: Experimental activities (e.g., problem-solving) used to study cognition. Measured by outcome variables (accuracy, reaction time, error).
• Processes: Hypothetical mental operations underlying behavior (e.g., attention, memory). Inferred from task performance patterns.
• Example: The recency effect (in memory tasks) suggests a short-term memory process.
• Complexities: Tasks often involve multiple overlapping processes. Theoretical assumptions guide task design. Brain studies refine our understanding but shouldn't directly equate tasks with individual processes.

Comparing Neuroscientific Techniques

• Correlational vs. Interventional Methods:
  • Correlational: Observe brain activity during tasks (EEG, fMRI, PET, MEG). Identifies patterns.
  • Interventional: Manipulate brain activity to study its behavioral effects (lesion studies, TMS, optogenetics). Provides stronger causal evidence.
• Spatial Resolution: Ability to pinpoint activity location (fMRI, PET, single-cell recording – high).
• Temporal Resolution: Precision of measuring when activity occurs (EEG, MEG, single-cell recording – high).
• Trade-offs: High spatial resolution often comes with low temporal resolution. Combining methods is crucial.

Experimental Ablation and Neuropsychology

• Ablation: Deliberate destruction of brain areas in animals to study behavioral effects. Reveals functional roles.
• Neuropsychology: Studies brain-damaged patients to understand function localization.
• Examples: Stroke studies identify language areas (Broca's and Wernicke's).
• Dissociations:
  • Single Dissociation: Impairment in one task, normal performance in another, suggesting partially separate processes. (e.g., verbal memory problems but intact visual memory).
  • Double Dissociation: Complementary patterns of impairment in two patients, strongly supporting distinct processes.
• Challenges: Localization issues (damage spanning multiple regions), unclear if damaged area is processing or relaying. Brain plasticity and medication effects, and generalizability from animals to humans.

Single-Cell Recording

• Description: Measures electrical activity of a single neuron using a microelectrode. Unique spatial and temporal precision.
• Applications: Animal studies analyzing neuronal responses to tasks (stimulus onset).
• Methodology: Careful task design, well-trained animals (operant conditioning).
• Strengths: High precision, direct neural activity measurement
• Limitations: Limited to animals, labor-intensive, and correlational in nature.

Measuring Electrical and Metabolic Activity

• Electroencephalography (EEG): Measures electrical activity from scalp electrodes. High temporal, low spatial resolution.
• Magnetoencephalography (MEG): Measures magnetic fields from brain activity; better spatial and temporal resolution than EEG. Expensive.
• Event-Related Potentials (ERPs): Average EEG/MEG responses to specific events. Useful for comparing conditions.
• Positron Emission Tomography (PET): Uses radioactive tracers to measure metabolic activity; high spatial but poor temporal resolution.
• Functional Magnetic Resonance Imaging (fMRI): Measures blood flow changes related to neural activity. High spatial, but low temporal resolution.

Stimulating the Brain

• Techniques: Electrical or chemical stimulation in animals, or TMS (transcranial magnetic stimulation) in humans.
• TMS: Non-invasive, temporarily disrupts neural activity in specific cortical areas. Used in virtual lesion studies and motor cortex assessment.
• Strengths: Reversible effects, non-invasive, precise timing.
• Limitations: Lower spatial precision, inability to reach deep areas, and transient effects.

Neurones and Glial Cells

• Neurones: Process and transmit information. Diverse shapes and sizes.
  • Dendrites: Receive signals.
  • Axons: Transmit signals.
  • Types: Multipolar, bipolar, unipolar.
• Glial Cells: Support neurons.
  • Astrocytes: Connect to blood vessels, nourishment, waste removal and blood-brain barrier.
  • Oligodendrocytes: Produce myelin (CNS). Schwann cells in PNS.
  • Microglia: Phagocytosis, immune functions.

The Resting Potential

• Neuronal membrane potential approximately -60 mV (inside negative).
• Ions (Na+, K+, Cl–, organic anions) contribute.
• Distribution: High extracellular Na+ and Cl–, high intracellular K+ and organic anions.
• Forces: Diffusion and electrostatic pressure.
• Sodium-Potassium Pump: Maintains resting potential.

The Action Potential

• Depolarization: Positive shift in membrane potential exceeding threshold triggers action potential.
• Voltage-Dependent Ion Channels: Sodium channels open first, then potassium channels, leading to depolarization and repolarization.
• All-or-None Principle: Action potential occurs fully or not at all (intensity not affected). Increased activity is reflected in firing rate, not amplitude.
• Propagation: Action potentials travel along axons. Myelination speeds up conduction (jumps between nodes of Ranvier).

Neural Integration

• Neurones integrate signals (EPSPs, IPSPs).
• EPSPs: Depolarize, increase firing likelihood.
• IPSPs: Hyperpolarize, decrease firing likelihood.
• Axon hillock summation determines whether threshold is reached.

Synaptic Transmission

• Communication between neurons at synapses.
• Release of Neurotransmitters: Synaptic vesicles release neurotransmitters into the synaptic cleft.
• Binding to Receptors: Neurotransmitters bind to receptors on the postsynaptic membrane (ionotropic or metabotropic).
• Termination of Signal: Neurotransmitters are removed via reuptake or enzymes.

Neurotransmitters and Neuropharmacology

• Neurotransmitters have specific roles (e.g., glutamate, dopamine).
• Drugs: Can influence neurotransmission by blocking or activating receptors, or affecting reuptake.
• Agonists: Increase receptor activity.
• Antagonists: Decrease receptor activity.

Sound Waves and Fourier Decomposition

• Sound Waves: Oscillations in a medium (e.g., air) causing compression and rarefaction. Represented as waveforms.
• Fourier Analysis: Decomposes complex waves into simpler sine waves based on frequency, intensity (amplitude), and phase.
• Timbre: Unique sound qualities differentiating sources producing the same note (multiple frequency components).

The Outer, Middle, and Inner Ear

• Outer Ear: Pinna and ear canal. Pinna directs sound waves, canal amplifies specific frequencies.
• Middle Ear: Tympanic membrane, ossicles (malleus, incus, stapes). Amplifies sound, protects against loud sounds.
• Inner Ear: Cochlea, basilar membrane, organ of Corti. Contains hair cells, converts vibrations to neural signals.

Pitch Coding

• Place Code: Different basilar membrane locations vibrate for different frequencies (high near base, low near apex).
• Temporal Code: Hair cells fire action potentials synchronously with low-frequency sound waves.

Sound Localization

• Cues: Interaural time difference (ITD) and intensity difference (IID) for localization. Pinna filtering adds directional cues.
• Superior Olive: Brain region processing ITD and IID (medial and lateral superior olive).

Auditory Cortex

• Primary Auditory Cortex (A1): Organized tonotopically (different regions respond to different frequencies). Processes basic auditory features.
• Surrounding Regions: Belt and parabelt areas process complex sounds.

Somatosensory Receptors

• Types: Free nerve endings (pain, temperature), mechanoreceptors (pressure, vibration — Merkel's disks, Ruffini corpuscles, Meissner's corpuscles, Pacinian corpuscles), proprioceptors (body position, movement).

Ascending Pathways

• Spinothalamic Tract: Pain and temperature.
• Dorsal Column-Medial Lemniscus Tract: Fine touch, proprioception.
• Spinocerebellar Tract: Proprioceptive information to cerebellum.

Sensory Homunculi

• Somatotopic map in somatosensory cortex (S1) representing body regions. Disproportionate representation for tactile-sensitive areas (hands, face).

Parietal Lobes

• IPS (Intraparietal Sulcus): Landmark organizing parietal area.
• Functional Regions: AIP (grasping), LIP (eye movements), VIP (multisensory), MIP (reaching). Human equivalents identified.
• Connectivity and Function: Integrates sensory information, plays roles in action planning, visual processing (dorsal stream), and connections to motor areas, basal ganglia, and cerebellum.

Basal Ganglia

• Structure: Striatum (caudate, putamen), globus pallidus (internal, external), subthalamic nucleus, substantia nigra.
• Inputs: Cortex, substantia nigra. Output specifically to cortex via thalamus, and to brainstem nuclei.

Cerebellum

• Structure: Divisions (anterior, posterior, floculonodular). Zones (vermis, intermediate, lateral). Correlates with nuclei.
• Inputs: Somatosensory info, vestibular system, extensive cortical input.
• Outputs: Projects via thalamus to motor regions.
• Functions: motor coordination, timing, error correction, and internal models in movement control.

Coordinate Transformations and Receptive Fields

• Challenge: Transforming visual (retinocentric) to body-centered references. Combining visual and proprioceptive information for action planning.
• Brain Areas: Parietal cortex converts input into coordinate systems relevant for action.

AIP - rPMv Grasp Circuit

• Areas: AIP (visual), rPMv (motor).
• Function: Linking visual object information to grasping actions; lesions impair visually guided grasps.

Somatotopic Representation in M1

• Motor Homunculus: Body map representing cortical representation. High representation for hand and face.
• Limitations: Neurons in M1 affect multiple muscles.

Force, Direction, and Population Codes in M1

• Parameters: Coding for force and direction of movement.
• Population Vectors: Combined activity from many neurons to predict movement direction.

Translating Between Abstract Codes and Muscle Activity

• Challenge: Linking abstract spatial plans to precise muscle activation. Complex relationship between limb position and joint angles.
• M1's Role: Converting spatial representations to movement commands.

Coordination and Cerebellar Function

• Internal Models: Forward dynamic models predict movement outcomes.
• Control Systems: Open-loop (predefined), closed-loop (feedback).
• Smith Predictor: Advance feedback using internal models to minimize delays.

Visual Perception (Overview)

• Visual processing from eye to primary visual cortex.
• Beyond primary visual cortex (orientation, movement, color).
• Higher perceptual abilities (object recognition) and disorders (agnosia).
• Faces as unique objects (special topic).

Primate Vision

• Significance of vision in primates: considerable cortical allocation.
• Stimulus: Light is the primary input.
• Visible Spectrum: Humans perceive a limited band between ~400-700 nm.

Anatomy of the Eye

• Structure & Function: Light focusing through cornea and lens, photoreceptors (rods and cones) in the retina. Optic nerve.
• Blind Spot: Region on retina where optic nerve exits; lacks photoreceptors. Demonstration with visual experiments.

Photoreceptors: Rods and Cones

• Rods: Highly sensitive to dim light, night vision; peripheral retina.
• Cones: Color vision, high acuity; primarily in fovea. Three types (S, M, L cones) for red, green, and blue. Wavelengths absorption.

Color Vision and Deficiencies

• Testing methods, color blindness types (protanopia, deuteranopia, tritanopia). Statistics (prevalence).