Biopsychology PDF

The Mind-Body Problem Key Philosophical Views: Dualism: ○ Proposed by philosophers like Descartes, dualism posits that the mind and body are two fundamentally different substances. ○ The mind is ethereal and non-physical, capable of influencing or controllin...

The Mind-Body Problem Key Philosophical Views: Dualism: ○ Proposed by philosophers like Descartes, dualism posits that the mind and body are two fundamentally different substances. ○ The mind is ethereal and non-physical, capable of influencing or controlling the physical body. ○ Dualists face the "interaction problem": how can two distinct substances interact causally? Materialism (Monism): ○ Materialism argues that only physical matter exists, and mental phenomena can be fully explained through physical processes. ○ Mental events such as memory, perception, and consciousness are understood as emergent properties of brain activity. ○ Contemporary neuroscience largely aligns with materialist perspectives, emphasizing the role of the brain in generating mental states. Relationship Between Tasks and Processes Tasks: ○ Tasks are experimental activities designed for participants to perform, such as solving problems, recalling information, or making decisions. ○ Performance is typically measured using outcome variables like accuracy, reaction time, or error rates. ○ Tasks aim to isolate and investigate specific aspects of cognition. Processes: ○ Processes refer to hypothetical mental operations that underlie observable behaviors, such as attention, memory encoding, or decision-making. ○ They are inferred rather than directly observed, based on patterns of behavior across tasks. ○ Example: The "recency effect" in memory tasks suggests a short-term memory process for retaining recent items. Key Considerations: ○ A task might involve multiple overlapping processes, complicating interpretation. ○ Theoretical assumptions about processes often guide task design. ○ Brain studies can refine our understanding of processes but require caution to avoid conflating tasks with specific processes. Comparing Neuroscientific Techniques Key Distinctions: 1. Correlational vs. Interventional Methods: ○ Correlational Methods: Observe brain activity while participants perform tasks. Techniques include EEG, fMRI, PET, and MEG. Useful for identifying patterns of brain activity associated with specific cognitive functions. ○ Interventional Methods: Directly manipulate brain activity to study its effects on behavior. Techniques include lesion studies, TMS, and optogenetics (in animals). Provide stronger evidence for causal relationships between brain regions and cognitive functions. 2. Spatial and Temporal Resolution: ○ Spatial Resolution: Refers to the ability to pinpoint where in the brain activity occurs. High spatial resolution techniques: fMRI, PET, single-cell recording. ○ Temporal Resolution: Refers to the precision of measuring when brain activity occurs. High temporal resolution techniques: EEG, MEG, single-cell recording. Trade-offs: Techniques with high spatial resolution (e.g., fMRI) often have poor temporal resolution, and vice versa. No single technique provides a complete picture; combining methods is essential to address complex questions. Experimental Ablation and Neuropsychology Ablation: ○ Involves the deliberate destruction or removal of specific brain areas in animals. ○ Allows researchers to determine how impairments in specific brain regions affect behavior. ○ Provides insights into the functional roles of different neural structures. Neuropsychology: ○ Focuses on studying patients with brain damage caused by injury, disease, or surgery. ○ Reveals information about the localization and specialization of cognitive functions. ○ Example: Studies of stroke patients have identified brain regions critical for language (e.g., Broca's and Wernicke's areas). Dissociations:  Single Dissociation: ○ A patient is impaired in one task but performs normally on another. ○ Suggests that the two tasks rely on partially independent processes. ○ Example: Impairment in verbal memory but intact visual memory. Double Dissociation: ○ Involves two patients with complementary patterns of impairment. ○ Example: One patient struggles with verbal memory but not visual memory, while another has the opposite pattern. ○ Strongly supports the idea that the two processes are distinct and rely on different brain mechanisms. Challenges: Localization Issues: ○ Brain damage often spans multiple regions, complicating precise localization of function. Relay vs. Processing: ○ Damaged regions might relay rather than directly process information. Plasticity and Medication: ○ The brain adapts to damage, potentially reorganizing functions. ○ Medications may affect brain activity and behavior. Generalization Issues: ○ Findings from animal studies may not fully translate to humans, particularly for uniquely human functions like language. Single-Cell Recording Description: ○ A microelectrode is inserted into the brain to measure the electrical activity of a single neuron. ○ Provides unparalleled spatial and temporal precision. Applications: ○ Often used in animal studies to examine neuronal responses during task performance. ○ Aligns neuronal activity with specific task events (e.g., stimulus onset). Methodology: ○ Requires careful task design and control conditions to isolate relevant neural activity. ○ Animals must be trained extensively using operant conditioning techniques. Strengths and Limitations: ○ Strengths: High precision in space and time, direct measurement of neural activity. ○ Limitations: Limited to animal studies, labor-intensive, and correlational in nature. ○ Combining with microstimulation can allow causal inferences. Measuring Electrical and Metabolic Activity Techniques: 1. Electroencephalography (EEG): ○ Measures electrical activity through scalp electrodes. ○ Advantages: High temporal resolution, non-invasive, relatively inexpensive. ○ Disadvantages: Poor spatial resolution, signals are distorted by the skull. 2. Magnetoencephalography (MEG): ○ Records magnetic fields produced by brain activity using SQUID devices. ○ Advantages: Better spatial precision than EEG, excellent temporal resolution. ○ Disadvantages: Expensive, limited availability. 3. Event-Related Potentials (ERPs): ○ Obtained by averaging EEG/MEG responses to specific events (e.g., stimulus onset). ○ Useful for comparing brain responses under different experimental conditions. 4. Positron Emission Tomography (PET): ○ Uses radioactive tracers to measure metabolic activity in the brain. ○ Advantages: High spatial resolution, useful for studying metabolic processes. ○ Disadvantages: Invasive, poor temporal resolution. 5. Functional Magnetic Resonance Imaging (fMRI): ○ Measures changes in blood flow and oxygenation (linked to neural activity). ○ Advantages: Excellent spatial resolution, non-invasive. ○ Disadvantages: Poor temporal resolution due to lag in metabolic responses. Stimulating the Brain Techniques: 1. Traditional Stimulation: ○ Involves electrical or chemical stimulation in animals to determine behavioral effects. ○ Provides insights into brain-behavior relationships. 2. Transcranial Magnetic Stimulation (TMS): ○ Non-invasive technique used in humans. ○ Applies magnetic fields to transiently disrupt neural activity in targeted cortical areas. Applications of TMS: Virtual Lesions: ○ Temporarily deactivate specific brain regions to study their roles in cognition. Motor Cortex Studies: ○ Evoke muscular responses to assess the preparatory state of motor areas. Strengths and Limitations: Strengths: ○ Reversible effects, non-invasive, and allows precise timing of disruptions. Limitations: ○ Limited spatial precision, cannot reach deep brain structures, and effects are transient. Neurones and Glial Cells The brain is composed of a variety of cell types, broadly categorized into neurones (spelled “neurons” in American English) and glial cells. Neurones: These cells are responsible for processing and transmitting information. They exist in many shapes and sizes and are often characterized based on the relationship between their soma (cell body), axons, and dendrites. ○ Dendrites: Meaning “trees,” dendrites are branched structures that receive signals from other neurones. ○ Axons: Long, slender tubes often insulated with myelin sheaths. Axons transmit information to other neurones by connecting to dendrites at terminal boutons (or buttons). ○ Types of neurones: Multipolar neurones: One axon and many dendrites, common in the central nervous system. Bipolar neurones: A single dendrite and one axon, typically sensory. Unipolar neurones: A single stalk that divides into one dendrite and one axon, also typically sensory. ○ Internally, neurones contain structures like the nucleus, housing DNA, and mitochondria, providing cellular energy. Glial Cells: These primarily support neurones. Major types include: ○ Astrocytes: Connect to blood vessels, provide nourishment, and remove waste. They contribute to the blood-brain barrier to shield neurones from harmful substances in the blood. ○ Oligodendrocytes: Produce myelin sheaths for neurones in the central nervous system. Outside the CNS, Schwann cells perform this function. ○ Microglia: Perform phagocytosis, engulfing and breaking down dead neurones, and serve immune functions to protect the brain from microorganisms. The Resting Potential At rest, neurones maintain a membrane potential of approximately -60 mV, where the inside of the cell is negatively charged relative to the outside.  Ions: Charged particles such as sodium (Na+), potassium (K+), chloride (Cl-), and organic anions contribute to the resting potential. Distribution: ○ Extracellular fluid contains high concentrations of Na+ and Cl- (positively charged overall). ○ Intracellular fluid has many organic anions and K+ (negatively charged overall). Forces influencing ion movement: ○ Diffusion: Ions move from areas of high to low concentration. ○ Electrostatic pressure: Opposite charges attract, influencing ion motion. Sodium-Potassium Pump: This active transport mechanism pumps sodium out and potassium in, maintaining the resting potential. The Action Potential Neurones generate electrical signals known as action potentials when depolarization (a positive shift in membrane potential) exceeds the threshold of excitation. Voltage-Dependent Ion Channels: ○ Sodium channels open first, allowing Na+ to rush in and depolarize the cell. ○ Potassium channels open as sodium channels close, leading to K+ exiting the cell and repolarization. ○ The membrane potential briefly dips below resting potential (hyperpolarization) before equilibrium is restored. All-or-None Principle: Action potentials occur fully or not at all, regardless of the strength of the stimulus. Increased activity is reflected in the rate of firing rather than the size of the action potentials. Propagation: ○ Action potentials travel along axons through passive transmission with regeneration at intervals. ○ Myelination speeds up conduction, allowing action potentials to jump between nodes of Ranvier, making transmission efficient. Neural Integration Neurones integrate multiple signals to decide whether to fire an action potential. These signals are: Excitatory Postsynaptic Potentials (EPSPs): Depolarize the postsynaptic membrane, making firing more likely. Inhibitory Postsynaptic Potentials (IPSPs): Hyperpolarize the membrane, making firing less likely. The summation of EPSPs and IPSPs at the axon hillock determines if the threshold of activation is exceeded, triggering an action potential. Synaptic Transmission Communication between neurones occurs at synapses. Key steps include: 1. Release of Neurotransmitters: ○ Synaptic vesicles in terminal boutons dock at the presynaptic membrane. ○ Action potentials open voltage-dependent calcium channels, allowing Ca2+ to enter and trigger vesicle fusion with the presynaptic membrane. ○ Neurotransmitters are released into the synaptic cleft. 2. Binding to Receptors: ○ Neurotransmitters diffuse across the synaptic cleft and bind to ionotropic or metabotropic receptors on the postsynaptic membrane. ○ Ionotropic receptors directly open ion channels, while metabotropic receptors involve additional intracellular processes. 3. Termination of Signal: ○ Remaining neurotransmitters are either reabsorbed (reuptake) or destroyed by enzymes. Neurotransmitters and Neuropharmacology Different neurotransmitters serve specific roles in brain function: Glutamate: A widespread excitatory neurotransmitter. Dopamine: Modulates motivation, reward, and movement, with projections from deep brain nuclei. Drugs can influence neurotransmission by: Blocking or activating receptors. Inhibiting reuptake or increasing neurotransmitter synthesis. Agonists: Increase receptor activity. Antagonists: Decrease receptor activity. Psychoactive drugs that cross the blood-brain barrier profoundly affect synaptic transmission, altering perception, mood, and cognition. Sound Waves and Fourier Decomposition Sound Waves: ○ Oscillations through a medium, such as air, create areas of compression (increased density) and rarefaction (decreased density). ○ These oscillations can be represented as a waveform, where the x-axis represents time and the y-axis represents intensity. Fourier Analysis:  ○ Any complex waveform can be mathematically decomposed into simpler sine waves, each characterized by: Frequency: Number of oscillations per second (measured in Hertz, Hz). Higher frequencies correspond to higher-pitched sounds. Intensity (Amplitude): Height of the sine wave, related to loudness; measured in decibels (dB). A 20 dB increase corresponds to a tenfold increase in sound pressure. Phase: The position within the wave cycle at a given point in time. Timbre: ○ Most natural sounds (e.g., musical instruments) are complex, containing multiple frequency components. ○ Timbre is the unique quality of sound that allows us to distinguish different sources producing the same note. The Outer Ear Components: ○ Pinna: The visible, external part of the ear. Its shape helps to collect and funnel sound waves into the ear canal. Plays a role in sound localization by filtering sound based on its direction. ○ Ear Canal: Amplifies sound within the range of 2000–5000 Hz due to its natural resonance. Protects the eardrum from debris and changes in temperature. The Middle Ear Components: ○ Tympanic Membrane: The eardrum, which vibrates in response to incoming sound waves. ○ Ossicles: Three small bones: Malleus (hammer): Connected to the eardrum. Incus (anvil): Acts as a bridge. Stapes (stirrup): Interfaces with the oval window of the cochlea. ○ Oval and Round Windows: Openings to the cochlea that facilitate the transfer of sound waves from air to fluid. Function: ○ Amplification: The tympanic membrane’s size relative to the smaller oval window concentrates sound pressure. Lever action of the ossicles further increases the force of vibrations. ○ Protection:  Stapedius and tensor tympani muscles dampen vibrations during loud sounds or self-generated noises (e.g., chewing, speech). The Inner Ear Cochlea: ○ Spiral-shaped structure with three chambers: Vestibular Canal: Upper chamber. Middle Canal: Houses the organ of Corti. Tympanic Canal: Lower chamber. ○ Basilar Membrane: Separates the middle and tympanic canals. Vibrates in response to sound, with different parts responding to different frequencies. Organ of Corti: ○ Contains inner and outer hair cells, which are sensory receptors for hearing. ○ Cilia on hair cells bend in response to movement, creating shearing forces. ○ Tip Links: Structures connecting cilia; when stretched, they open ion channels, allowing potassium to enter and depolarize the cell. Pitch Coding Place Code: ○ The basilar membrane’s varying thickness and width allow specific locations to resonate with specific frequencies. ○ Higher frequencies resonate near the base (closer to the oval window), and lower frequencies near the apex. Temporal Code: ○ Hair cells fire action potentials in synchrony with the sound wave phase for low-frequency sounds. ○ The time interval between spikes provides frequency information. Sound Localization Cues for Localization: ○ Interaural Time Difference (ITD): Sound arrives at the closer ear slightly earlier. Effective for low frequencies, as the temporal coding is more precise. ○ Interaural Intensity Difference (IID): Sound is louder in the closer ear, especially for high frequencies, which are more attenuated by the head (acoustic shadow). ○ Pinna Filtering:  The pinna modifies sound frequency components based on direction, helping determine elevation. Superior Olive: ○ Combines input from both ears: Medial Superior Olive: Processes ITD. Lateral Superior Olive: Processes IID. Auditory Cortex Primary Auditory Cortex (A1): ○ Organized tonotopically, with different regions responding to different frequencies. ○ Processes basic auditory features, such as pitch and loudness. Surrounding Regions: ○ Belt and Parabelt Areas: Respond to complex sounds, such as human speech and environmental noises. ○ Important for higher-level auditory perception, including recognition and interpretation of sounds. Somatosensory Receptors Types of Receptors: 1. Free Nerve Endings: Detect pain and temperature. 2. Mechanoreceptors: Detect mechanical pressure and vibration: Merkel’s Disks: Slow adapting, small receptive fields (fine touch). Ruffini Corpuscles: Slow adapting, large receptive fields (skin stretch). Meissner’s Corpuscles: Fast adapting, small receptive fields (light touch). Pacinian Corpuscles: Fast adapting, large receptive fields (vibration). 3. Proprioceptors: Found in muscles, tendons, and joints; inform the brain about body position and movement. The Ascending Pathways Spinothalamic Tract: ○ Transmits pain and temperature signals. ○ Slower conduction speed due to thinner axons. Dorsal Column-Medial Lemniscus Tract: ○ Transmits fine touch and proprioception signals. ○ Fast conduction due to myelinated axons. Spinocerebellar Tract:  ○ Transmits proprioceptive information directly to the cerebellum, without crossing. Sensory Homunculi Somatotopic Map: ○ Body regions represented in primary somatosensory cortex (S1) according to their physical location. ○ Hands, lips, and face have disproportionately large cortical representation due to higher receptor density. Functional Implications: ○ Larger cortical areas correspond to greater tactile acuity and discrimination abilities (e.g., fingertips vs. back). 1. Anatomy of the Parietal Lobes Intraparietal Sulcus (IPS): ○ Useful landmark for parietal orientation. ○ Monkeys: Area 5: Located above the IPS (superior parietal lobule). Area 7: Located below the IPS (inferior parietal lobule). ○ Humans: The sulcus has a more anterior-posterior orientation. Both areas 5 and 7 lie above the IPS in the superior parietal lobule. Inferior parietal lobule comprises additional regions with no direct equivalents in monkeys. Functional Regions in Monkeys’ IPS: ○ AIP (Anterior): Associated with grasping and object-related actions. ○ LIP (Lateral): Linked to eye movements. ○ VIP (Ventral): Processes multisensory integration. ○ MIP (Medial): Involved in reaching movements. ○ Approximate human equivalents identified within IPS. Connectivity and Function: ○ Receives and integrates sensory information. ○ Termination point for the dorsal visual stream. ○ Heavily connected to the somatosensory cortex. ○ Projects cortically to prefrontal, premotor, and primary motor areas and subcortically to the basal ganglia and cerebellum. ○ Damage to the superior parietal lobes may cause optic ataxia (misreaching, poor hand shaping during grasping). 2. Non-Primary Motor Areas Brodmann Area 6:  ○ Premotor Area (PMA): Lateral section, visible externally. ○ Supplementary Motor Area (SMA): Medial section, visible on the inner wall of the hemisphere. Cingulate Motor Areas: ○ Located below SMA on the medial wall. ○ Receive major inputs from the parietal lobes and some from prefrontal areas. ○ Specific pathways identified in monkeys for reaching, grasping, and eye movements. 3. Primary Motor Cortex (M1) and Descending Motor Tracts Location: ○ Anterior to the central sulcus. ○ Extends to lateral and medial hemispheric walls. Connections: ○ Extensive inputs from premotor cortex, SMA, cingulate motor areas, primary somatosensory cortex, and subcortical motor regions. Descending Motor Tracts: ○ Corticospinal Tract: Originates in the cerebral cortex. Lateral Corticospinal Tract: Fibres decussate (cross) in the brainstem, controlling contralateral movements, especially fine hand and finger movements. Ventromedial Corticospinal Tract: Uncrossed fibres; involved in posture and gross movements. ○ Corticobulbar Tract: Controls head muscles (e.g., tongue). ○ Collectively referred to as the pyramidal tracts. Subcortical Tracts: Originate from non-cortical regions but may receive cortical inputs. 4. Basal Ganglia: Anatomy and Connectivity Structure: ○ Subcortical nuclei include the striatum (caudate and putamen), globus pallidus (internal and external segments), subthalamic nucleus, substantia nigra (pars compacta and pars reticulata). Inputs: ○ Cortical regions, especially motor areas. ○ Substantia nigra pars compacta. Outputs: ○ From GPi and SNr to cortex via the thalamus. ○ Outputs are specific and form closed loops with originating cortical areas. ○ Additional projection to brainstem motor nuclei for posture and tone control. 5. Cerebellum: Anatomy and Function Structure:  ○ Located beneath temporal and occipital lobes, behind the spinal cord. ○ Divisions: Anterior, Posterior, and Floculonodular Lobes (deep fissures). Medial (vermis), Intermediate, and Lateral Zones: Vermis connects to fastigial nucleus. Intermediate zone connects to interposed nuclei. Lateral zone connects to dentate nucleus. ○ Cortex and subcortical nuclei. Inputs: ○ Somatosensory information from the spinal cord. ○ Vestibular nucleus. ○ Extensive cortical input (30 million fibres). Outputs: ○ Projects to motor regions via the thalamus. 6. Coordinate Transformations and Receptive Fields Challenges: ○ Translating visual (retinocentric) input to body-centred reference frames. ○ Combining proprioceptive and visual information for coordinated movement. Brain Areas: ○ Early visual cortical cells: Retinotopic receptive fields. ○ Parietal cortex: Represents stimuli in various coordinate systems, essential for action planning. 7. AIP – rPMv Grasp Circuit Areas Involved: ○ AIP: Visual-dominant neurons, processes depth and 3D features of objects. ○ rPMv: Motor-dominant neurons, associated with grasping movements. Function: ○ Lesions impair visually guided grasping but not tactile-guided grasping. 8. Somatotopic Representation in M1 Motor Homunculus: ○ Body map reflecting cortical representation. ○ Areas like hands and lips are disproportionately large due to functional importance. Controversies: ○ Neurons in M1 influence multiple related muscles. 9. Force, Direction, and Population Codes in M1 Parameters: ○ Sensitive to force during tasks (e.g., precision grip). ○ Broadly tuned for movement directions. Population Vectors:  ○ Combined activity of many neurons accurately predicts movement direction. 10. Translating Between Abstract Codes and Muscle Activity Challenges: ○ Convert external spatial plans into muscle commands. ○ Relationship between joint angles and limb positions is complex. M1’s Role: ○ Converts spatial representations into muscle commands. 11. Coordination and Cerebellar Function Internal Models: ○ Forward dynamic models: Predict movement outcomes based on motor commands. ○ Forward sensory/output models: Predict sensory consequences of movements. Control Systems: ○ Open-loop: Predefined movements without feedback during execution. ○ Closed-loop: Feedback-driven corrections during movement. Smith Predictor: ○ Advanced feedback system using internal models to minimize sensory delays. Overview of the Lecture 1. Visual Perception from the Eye to the Primary Visual Cortex 2. Vision Beyond the Primary Visual Cortex: ○ Analyses of Orientation, Movement, and Color 3. Higher Perceptual Abilities: ○ Recognition of Objects ○ Disorders of Visual Recognition (Agnosias) 4. Special Topics: ○ Are Faces Special Objects? ○ Visual Illusions 1. Importance of Vision in Primates Cortical Allocation: ○ Approximately 50% of the primate cortex is dedicated to visual perception, underscoring its critical role. Stimulus: ○ The primary stimulus in the visual system is light, a form of electromagnetic energy.  Visible Spectrum: ○ Humans can perceive only a small band of the electromagnetic spectrum, primarily between 400 nm (violet)and 700 nm (red) wavelengths. 2. The Anatomy of the Eye a. Structure and Function Cornea and Lens: ○ Light enters the eye through the cornea, which along with the lens, focuses it onto the retina. Retina: ○ Contains photoreceptors (rods and cones) that convert light into neural signals. Optic Nerve: ○ Transmits visual information from the retina to the brain. b. The Blind Spot Definition: ○ The blind spot is the region on the retina where the optic nerve exits the eye; it lacks photoreceptors. Demonstration: ○ Experiment: With the left eye closed, focus the right eye on a plus sign while moving the page closer and farther. ○ Observation: At approximately 20 centimeters from the face, the green circle disappears as its image falls on the blind spot. 3. Photoreceptors: Rods and Cones a. Rods Function: ○ Highly sensitive to dim light. ○ Responsible for night vision. Distribution: ○ Predominantly located in the peripheral regions of the retina. Absorbance: ○ Rods absorb light across a wide range of wavelengths but are not color-sensitive. b. Cones Function: ○ Responsible for color vision and high-acuity vision.  Types: ○ S-Cones (Short-wavelength): Sensitive to blue light (~420 nm). ○ M-Cones (Medium-wavelength): Sensitive to green light (~534 nm). ○ L-Cones (Long-wavelength): Sensitive to red light (~564 nm). Distribution: ○ Concentrated in the fovea, the central part of the retina, providing sharp central vision. c. Absorbance of Light by Rods and Cones Graph Interpretation: ○ Shows the relative absorbance of various wavelengths by rods and each cone type. ○ Highlights the peak sensitivity wavelengths for each photoreceptor type. 4. Color Vision and Deficiencies a. Testing for Color Vision Method: Individuals are shown images with numbers embedded in colored circles. The task is to identify the number within the circle. Types of Color Vision Deficiencies: 1. Protanopia (Red-Blindness): ○ Deficit: Difficulty distinguishing red. ○ Cause: "Red" cones contain green cone opsin instead of red. 2. Deuteranopia (Green-Blindness): ○ Deficit: Difficulty distinguishing green. ○ Cause: "Green" cones contain red cone opsin instead of green. 3. Tritanopia (Blue-Blindness): ○ Deficit: Difficulty distinguishing blue. ○ Cause: Absence of blue cones. b. Color Blindness Statistics Prevalence: ○ Males: ~7-10% affected. ○ Females: