Behavioral Neuroscience Study Guide Flashcards

Foundations and Scope of Behavioral Neuroscience

• Definition of Behavioral Neuroscience:

  • Neuroscience encompasses the comprehensive study of the nervous system.

  • Behavioral Neuroscience specifically investigates the biological and neural mechanisms underlying mental processes, cognitive functions, and observable behaviors.

  • The human brain contains approximately $100\,\text{billion}$ ($10^{11}$) neurons, forming intricate networks across multidisciplinary domains.

  • The field integrates knowledge from diverse disciplines including cognitive science, computer science, artificial intelligence, psychiatry, neurology, physiology, biochemistry, pharmacology, immunology, endocrinology, genetics, developmental neurobiology, evolutionary biology, and anthropology.

Historical Milestones and Key Figures

• Aristotle:

  • Proposed cardiocentrism, asserting that the heart was the primary organ of mental processes and seat of intelligence, viewing the brain merely as a cooling mechanism for blood.

• Hippocrates:

  • Disagreed with cardiocentrism, identifying the brain as the true "seat of thoughts and emotions."

• Galen:

  • Greco-Roman physician who treated injured gladiators.

  • Documented that localized brain trauma directly altered specific behaviors and physical abilities, providing empirical support for brain-behavior relationships.

• Leonardo da Vinci:

  • Pioneered anatomical drawing by dissecting human cadavers.

  • Cast molten wax into brain ventricles to create detailed models of neuroanatomy, illustrating internal fluid structures ("aqueducts").

• René Descartes:

  • Conceptualized bodily movements and behavioral reactions as automatic mechanical reflexes.

  • Formulated Dualism: the philosophical view that the physical body and the non-physical mind/spirit are distinct entities.

  • Designated the pineal gland as the physical locus where the mind interacts with the body.

• Phrenology:

  • Historical theory asserting that individual character traits, faculties, and mental capabilities are localized in specific brain regions.

  • Believed that skull bumps directly reflected enlargement of underlying brain tissue responsible for distinct personality traits.

• Paul Broca:

  • Discovered language localization in the human brain through clinical-pathological correlation.

  • Demonstrated that damage to a specific region of the left frontal lobe (Broca's area) causes expressive language deficits.

  • Functions associated with Broca's area include speech production, sentence structure building, language comprehension, applying grammar rules, silent reading, speech rhythm processing, movement planning for speaking/writing, and action imitation.

• Korbinian Brodmann:

  • mapped the cerebral cortex cytoarchitectonically into 52 distinct regions based on cellular organization and organization patterns.

• Santiago Ramón y Cajal:

  • Formulated the Neuron Doctrine using Golgi staining techniques.

  • Established that the nervous system consists of discrete, individual, contiguous cells rather than a continuous interconnected syncytium/network, communicating across minute gaps.

• Donald Hebb:

  • Defined Hebbian Synapses: synaptic connections that alter their strength and connectivity as a result of experience or learning.

  • Summarized by the neuroscientific principle: "Cells that fire together wire together."

  • Introduced foundational principles of neuroplasticity and adult neurogenesis (the biological generation of new neurons within the adult brain).

• Alan Hodgkin & Andrew Huxley:

  • Utilized the giant axon of the squid (Loligo) to elucidate the biophysical mechanisms of neuronal action potentials and ion channel dynamics.

Experimental Research Methodologies

• Correlational Methods:

  • Measures co-variations between two variables to determine if a statistical relationship exists.

  • Core Rule: Correlation does not establish causation.

• Correlation Directionalities:

  • Positive Correlation: Both variables change in the same direction simultaneously (both increase or both decrease).

  • Negative Correlation: Variables change in opposite directions (as one variable increases, the other decreases).

  • No Correlation: No discernable pattern or statistical relationship exists between variables.

• Somatic vs. Behavioral Correlational Examples:

  • Correlating brain size with learning test performance scores.

  • Correlating circulating hormone levels with strength of mating behavior.

  • Correlating enlarged cerebral ventricles with severity of schizophrenic symptoms.

• Experimental Methods:

  • Investigates true cause-and-effect relationships through deliberate manipulation of variables under controlled conditions.

• Intervention Categories:

  • Somatic Intervention: Manipulating a physical, biological, or neural structure/function (Independent Variable) to measure resulting changes in behavior (Dependent Variable).

    • Example: Administering a hormone to observe changes in mating strength.

    • Example: Electrically stimulating a brain region to observe movement toward a goal object.

    • Example: Severing nervous system connections to observe changes in stimulus recognition.

- **Behavioral Intervention**: Manipulating an animal's environment, experience, or behavior (Independent Variable) to measure resulting changes in internal somatic structure or physiological function (Dependent Variable).
  - *Example*: Placing a male animal in the presence of a female to measure changes in circulating hormone levels.
  - *Example*: Presenting a visual stimulus to record changes in cortical electrical activity.
  - *Example*: Administering training exercises to measure anatomical structural changes in nerve cells.

• Experimental Design Components:

  • Independent Variable (IV): Factor directly manipulated by the experimenter.

  • Dependent Variable (DV): Factor measured to assess the effect of the IV manipulation.

  • Control Variables: Extraneous environmental or physiological factors kept constant to prevent confounding effects on the DV.

  • Experimental Group: Subjects exposed to the specific experimental IV manipulation.

  • Control Group: Baseline subjects treated identically to the experimental group except they do not receive the active IV manipulation.

• Types of Study Designs:

  • Between-Subjects Design: Uses distinct, separate groups of participants (one experimental, one control) running concurrently.

  • Within-Subjects Design: Tests a single group of participants before and after exposure to the IV manipulation; baseline pre-treatment measurements serve as the control condition.

• Methodological Case Examples:

  • Scenario 1: A study examining social media usage and self-reported anxiety via surveys gathers non-experimental correlational data (daily screen time co-varying with anxiety scores).

  • Scenario 2 (Sperry's Frog Visual System Experiment): Roger Sperry manipulated frogs by surgical rotation of eyeballs $180^\text{o}$ and cutting the optic nerve in an experimental group while maintaining an unmanipulated control group to evaluate visual tract regeneration—a between-subjects somatic intervention experiment.

Neuroanatomical Planes and Spatial Directions

• Anatomical Slicing Planes:

  • Horizontal Plane: Cuts parallel to the horizon, dividing the brain into superior (upper) and inferior (lower) portions.

  • Coronal (Frontal) Plane: Cuts vertically from ear to ear, dividing the brain into anterior (front) and posterior (back) sections.

  • Sagittal Plane: Cuts vertically along the longitudinal axis, dividing the brain into left and right hemispheres. A cut directly along the midline is termed midsagittal.

• Directional Orientations:

  • Superior / Inferior: Above / Below.

  • Anterior / Posterior: In front of / Behind.

  • Dorsal / Ventral: Towards the back or top of head / Towards the belly or underside.

  • Rostral / Caudal: Towards the beak/nose / Towards the tail or posterior spinal cord.

  • Medial / Lateral: Towards the central midline / Towards the outer sides.

  • Proximal / Distal: Near the center or origin / Farther away from the center or origin.

  • Ipsilateral / Contralateral: Located on the same side of the body / Located on opposite sides of the body.

Structural Subdivisions of the Human Nervous System

• Hierarchical Classification:

• Central Nervous System (CNS):

  • Composed exclusively of the Brain and Spinal Cord.

  • Cerebral Cortex Architecture:

  • Consists of two cerebral hemispheres.

  • Characterized by six distinct cellular layers composed of cell bodies, dendrites, and axonal processes.

  • Grey Matter: Composed predominantly of neuronal cell bodies, dendrites, and unmyelinated synapses (located along the outer cortical shell and subcortical nuclei).

  • White Matter: Composed of myelinated axon tracts beneath the cortex that facilitate long-distance neural communication.

• Cortical Topography:

  • Gyri (singular: Gyrus): Elevated ridges or bumps on the cortical surface.

  • Sulci (singular: Sulcus): Shallow grooves or fissures separating gyri.

• Cortical Lobes & Boundaries:

  • Frontal Lobe: Governs motor execution, higher executive function, decision-making, and critical thinking.

    • Precentral Gyrus: Located immediately anterior to the central sulcus; contains the primary motor cortex.

  • Parietal Lobe: Processes somatosensory inputs and spatial awareness.

    • Postcentral Gyrus: Located immediately posterior to the central sulcus; contains the primary somatosensory cortex.

  • Temporal Lobe: Processes auditory information, speech comprehension, language, learning, and memory encoding.

  • Occipital Lobe: Processes visual inputs.

  • Central Sulcus: Major structural divider separating the frontal lobe from the parietal lobe.

  • Sylvian Fissure (Lateral Sulcus): Deep boundary dividing the temporal lobe from the overlying frontal and parietal lobes.

• Seven Principal Anatomical Divisions of the CNS:

  1. Spinal Cord: Receives and processes sensory inputs from skin, joints, and muscles; executes motor commands to the body.

  2. Cerebellum: Maintains motor control, balance, posture, motor learning, and precise movement coordination.

  3. Medulla Oblongata: Brainstem structure controlling essential autonomic biological survival functions (respiration, heart rate, blood pressure).

  4. Pons: Brainstem bridge relaying motor velocity and spatial movement information from cerebral hemispheres to the cerebellum.

  5. Midbrain (Mesencephalon): Coordinates motor and sensory functions (ocular movements, auditory/visual reflexes).

  • Superior Colliculi: Visual processing and orienting reflexes.

  • Inferior Colliculi: Auditory signal processing and reflex integration.

  • Substantia Nigra: Dopaminergic nucleus integral to motor control pathways of the basal ganglia.

  • Reticular Formation: Diffuse brainstem core regulating arousal, alertness, and sleep cycles.

  • Periaqueductal Gray: Central grey matter involved in pain perception, modulation, and defensive behaviors.

  1. Diencephalon:

  • Thalamus: Mandatory gateway and processing relay station for almost all sensory pathways sending information to the cerebral cortex.

  • Hypothalamus: Primary regulatory center controlling autonomic, neuroendocrine, metabolic, visceral, and drive states.

  1. Cerebrum:

  • Basal Ganglia: Subcortical motor control network comprising the Caudate Nucleus, Putamen, and Globus Pallidus.

  • Hippocampus: Medial temporal lobe structure crucial for declarative memory formation, consolidation, and spatial navigation.

  • Amygdala: Medial temporal structure coordinating autonomic, emotional, and neuroendocrine responses to threats and emotional stimuli.

• Deep Subcortical Networks:

  • Limbic System: Interconnected circuit managing emotion, memory processing, learning, and drive behaviors. Comprises the hippocampus, fornix, amygdala, cingulate gyrus, olfactory bulb, thalamus, septal nuclei, mammillary bodies, stria terminalis, and hypothalamus.

• Peripheral Nervous System (PNS):

  • Extends throughout the body outside the skull and spinal column.

  • Sensory Nerves: Afferent fibers carrying environmental and visceral somatic inputs toward the CNS.

  • Motor Nerves: Efferent fibers carrying action commands from the CNS to effector skeletal muscles, organs, and glands.

  • Somatic Nervous System:

  • Innervates skeletal muscles and somatic sensory organs.

  • Cranial Nerves: 12 paired nerves emerging directly from the brainstem and brain.

- *Functional Category Mnemonic Rule*: **S** = Sensory, **M** = Motor, **B** = Both.
- **Spinal Nerves**: 31 pairs connected to spinal cord segments.
  - *Cervical*: 8 segments.
  - *Thoracic*: 12 segments.
  - *Lumbar*: 5 segments.
  - *Sacral*: 5 segments.
  - *Coccygeal*: 1 segment.
  - *Mnemonic for Segment Sequence*: **C**ount **T**heir **L**ast **S**econds (**C**ervical, **T**horacic, **L**umbar, **S**acral).

• Autonomic Nervous System (ANS):

  • Controls involuntary autonomic organ activity, smooth muscle, cardiac muscle, and internal glands.

  • Sympathetic Nervous System: Activates "Fight or Flight" responses (prepares body for energetic expenditure and physical exertion).

  • Parasympathetic Nervous System: Mediates "Rest and Digest" pathways (conserves energy, promotes digestion, reduces heart rate).

    • Memory Aid: PARA = parachute (floating down slowly) or stop.

Neurophysiology and Resting Membrane Biophysics

• Electrophysiological Principles:

  • The interior of a resting neuron maintains an electrical potential negative relative to the extracellular fluid, ranging between $-50\,\text{mV}$ and $-90\,\text{mV}$ (typically averaged at $-65\,\text{mV}$ to $-70\,\text{mV}$).

  • The internal negativity stems from trapped intracellular organic anions ($\text{A}^-$), proteins, and nucleic acids.

  • Neurons exist bathed in an extracellular fluid rich in sodium ($\text{Na}^+$) and chloride ($\text{Cl}^-$) ions.

• Biophysical Forces Governing Ion Movement:

  • Electrostatic Forces: Electrical attraction of opposite charges and repulsion of like charges.

  • Diffusion (Concentration Gradient): Thermodynamic movement of particles down their concentration gradient from an area of high concentration toward an area of low concentration.

• The Sodium-Potassium Pump ($\text{Na}^+/\text{K}^+$ ATPase):

  • Active transport protein that uses chemical energy to maintain resting membrane potential and ionic concentration gradients across the lipid bilayer.

  • Operates against steep concentration gradients requiring metabolic hydrolysis of Adenosine Triphosphate (ATP) to Adenosine Diphosphate (ADP).

  • Stoichiometry: Expels $3\,\text{Na}^+$ ions OUT of the cell for every $2\,\text{K}^+$ ions brought IN.

  • Step-by-Step Molecular Transport Cycle:

  1. Three intracellular $\text{Na}^+$ ions bind to high-affinity intracellular sites on the pump.

  2. ATP transfers a phosphate group to the pump protein (phosphorylation), converting ATP to ADP.

  3. Phosphorylation induces a conformational change, opening the protein outward and releasing $3\,\text{Na}^+$ into the extracellular fluid.

  4. Two extracellular $\text{K}^+$ ions bind to high-affinity extracellular sites on the open transporter (dephosphorylation).

  5. Dephosphorylation causes the protein channel to revert to its original inward-facing conformation.

  6. Two $\text{K}^+$ ions are released inside the cell cytoplasm.

Action Potential Generation and Propagation

• Action Potential Phases and Channel Dynamics:

  • Resting State:

  • Voltage-gated $\text{Na}^+$ (VG $\text{Na}^+$) and voltage-gated $\text{K}^+$ (VG $\text{K}^+$) channels remain closed.

  • Passive $\text{K}^+$ leak channels remain open constantly, allowing baseline potassium permeability.

• Sub-Threshold Depolarization & Graded Potentials:

  • Small incoming electrical shifts (graded potentials) fluctuate across the soma and dendrites.

  • Graded potentials are proportional to stimulus intensity but decay over distance and time.

  • Boulder Metaphor: Sub-threshold push moves a boulder slightly without displacing it over an edge; once threshold force is reached, the boulder falls completely off the cliff automatically (All-or-None Law).

• Threshold Elevation ($\approx -55\,\text{mV}$):

  • Action potential initiation occurs at the axon hillock when Excitatory Postsynaptic Potentials (EPSPs) outweigh Inhibitory Postsynaptic Potentials (IPSPs) sufficiently to depolarize the membrane to threshold.

• Depolarization Phase (Upstroke):

  • Reaching threshold triggers rapid opening of activation gates on VG $\text{Na}^+$ channels.

  • $\text{Na}^+$ ions rush inward down both concentration and electrostatic gradients, driving membrane potential toward $\text{Na}^+$ equilibrium potential ($\approx +40\,\text{mV}$).

• Absolute Refractory Period:

  • At peak overshoot ($\approx +40\,\text{mV}$), an inactivation gate (a intracellular structural domain termed the ball-and-chain mechanism) physically blocks the interior channel pore of VG $\text{Na}^+$ channels.

  • VG $\text{Na}^+$ channels become fully inactivated and cannot reopen regardless of stimulus strength.

  • Ensures unidirectional action potential propagation down the axon.

• Repolarization Phase:

  • Inactivation of VG $\text{Na}^+$ channels halts $\text{Na}^+$ influx.

  • VG $\text{K}^+$ channels open fully, allowing $\text{K}^+$ ions to rush out of the cell driven by concentration gradients and internal electrostatic repulsion.

• Relative Refractory Period / Hyperpolarization:

  • Persistent outward flow of $\text{K}^+$ through slow-closing VG $\text{K}^+$ channels causes membrane potential to dip lower than resting level (undershoot/hyperpolarization to $\approx -80\,\text{mV}$).

  • VG $\text{Na}^+$ channel inactivation gates reset to a closed state.

  • A second action potential can be triggered during this window, but requires a significantly larger depolarizing current due to the hyperpolarized baseline.

  • Myelination and Saltatory Conduction:

• Myelin Sheath: Concentric layers of glial cell membranes (Schwann cells in PNS, Oligodendrocytes in CNS) wrapped around axons to provide high electrical resistance and low membrane capacitance.

• Nodes of Ranvier: Unmyelinated gaps along the axon rich in VG $\text{Na}^+$ channels.

• Saltatory Conduction: Depolarization passively travels inside the insulated internode at fast speeds, "jumping" from node to node where the action potential is regenerated.

  • Etymology: Derived from Spanish/Latin saltar ("to jump").

Integration of Postsynaptic Signals: Summation

• Spatial Summation:

  • Integration of postsynaptic potentials originating simultaneously from different physical locations (multiple presynaptic terminals) across the dendritic tree and soma.

  • If the algebraic sum of localized EPSPs and IPSPs reaching the axon hillock exceeds threshold, an action potential fires.

• Temporal Summation:

  • Integration of postsynaptic potentials occurring at the same physical synapse in rapid succession over time.

  • High-frequency presynaptic firing causes successive EPSPs to stack together before earlier potentials decay, depolarizing the hillock to threshold.

Synaptic Transmission Step-by-Step Mechanisms

1. Action Potential Arrival: Propagation of an action potential reaches the presynaptic axon terminal membrane.

2. Calcium Influx: Terminal membrane depolarization triggers opening of voltage-gated calcium channels, driving an influx of extracellular calcium ($\text{Ca}^{2+}$) ions into the axon terminal.

3. Vesicle Exocytosis: Intracellular $\text{Ca}^{2+}$ elevation triggers synaptic vesicles packed with neurotransmitters to fuse with the presynaptic active zone membrane, releasing neurotransmitter molecules into the synaptic cleft via exocytosis.

4. Receptor Binding: Transmitters diffuse across the cleft and bind to specific postsynaptic receptor proteins, opening ligand-gated ion channels and producing local EPSPs or IPSPs.

5. Postsynaptic Potential Spread: Postsynaptic potentials spread passively across dendrites and soma toward the axon hillock.

6. Inactivation and Termination of Signal:

   • 6a. Enzymatic Cleavage: Enzymes in the extracellular synaptic cleft rapidly break down excess neurotransmitter molecules (e.g., Acetylcholinesterase cleavage of Acetylcholine).

   • 6b. Reuptake Transporters: Transporter proteins clear neurotransmitter molecules from the cleft back into the presynaptic terminal or surrounding astrocytes for recycling.

7. Autoreceptor Regulation: Neurotransmitters bind to presynaptic autoreceptors, providing feedback inhibition to downregulate excess transmitter synthesis and subsequent exocytosis.

Clinical Electrophysiology: EEGs and Seizure Pathology

• Electroencephalography (EEG):

  • Non-invasive electrophysiological method using scalp electrodes to record macro-level sum electrical activity (post-synaptic potentials) across cortical networks.

  • Event-Related Potentials (ERPs): Standardized average electrical wave responses picked up by EEG directly tied to specific sensory, cognitive, or motor stimuli presentations.

• Pathophysiology of Seizures:

  • Normal cortical network activity exhibits asynchronous neuron firing patterns. During a seizure, large neuronal populations undergo abnormally synchronized, high-frequency hypersynchronous firing bursts.

• Classification of Seizure Disorders:

  • Tonic-Clonic Seizures (Formerly Grand Mal):

  • Widespread bilateral brain involvement.

  • Results in sudden loss of consciousness accompanied by severe violent motor contractions (tonic body stiffening followed by clonic rhythmic jerking).

  • Partial Seizures (Formerly Petit Mal or Absence Seizures):

  • Localized to focused brain areas.

  • Characterized by brief spike-and-wave discharge bursts, momentary lapses in awareness, and minor motor symptoms; frequently go undiagnosed.

  • Complex Partial Seizures:

  • Seizures originating within restricted brain regions (often temporal lobe) that impair consciousness or awareness.

  • Frequently preceded by a distinct aura (sensory illusions, metallic tastes, unusual visual/olfactory hallucinations).