Nervous System and Dog Cognition (copy)

Nervous System: Organizing Behavior

• The nervous system organizes perception and behavior in animals.

• It acts as the central processing unit coordinating sensory input and motor output.

• The lecture will cover sensory systems, motor output pathways, developmental aspects, and comparative aspects of the dog brain relative to other mammalian brains.

• The second part of the lecture will discuss examples of dog cognition pertinent to human-animal interactions.

The Brain and Nervous System

• When referring to the brain, it is shorthand for the entire nervous system, including the spinal cord and peripheral nerves.

• Peripheral nerves innervate the arms, legs, and face, entering and exiting the spinal cord and brain.

• Cranial nerves are located in the brain and control vital functions such as heart rate, digestion, and breathing, often without conscious awareness.

• The wolf brain is virtually indistinguishable from a dog brain at a gross inspection level, with size variations depending on the breed.

Mammalian Brains: Size and Gyration

• Mammalian brains vary significantly in size, from the common shrew to the elephant.

• Two key features distinguishing mammalian brains are size and the degree of gyration (foldedness) of the cerebral hemispheres.

Brain Size vs. Body Size

• A scatter plot of brain size (y-axis) versus body size (x-axis) on a log-log scale reveals a straight line relationship with a slope of approximately 0.75.

• The equation for the relationship is expressed via slope: slope \approx 0.75

• This slope indicates that larger animals tend to have smaller brains relative to their body size.

• The average mammalian trend can be represented as a line through the data points, allowing comparison of individual species.

• Animals with brains smaller than predicted fall below the line, while those with larger brains fall above the line.

• The human brain deviates significantly from the average mammalian trend, being much larger than expected for its body size.

• Dogs fall almost exactly on the average line, indicating a typical brain-body weight relationship for carnivores.

Encephalization Quotient

• The encephalization quotient (EQ) is the ratio of observed brain size to predicted brain size based on the average mammalian trend.

• EQ = \frac{Observed Brain Size}{Predicted Brain Size}

• Dogs have an EQ of approximately 1.0, indicating an average brain size relative to body size.

• Humans have a significantly higher EQ of around 7.0.

• Manatees have a much lower EQ, around 0.25, indicating a smaller brain than predicted for their body size.

Cerebral Hemisphere Gyration

• The cerebral hemispheres in mammalian brains exhibit varying degrees of folding or gyration.

• Folding creates hidden cortex within the depths of the sulci (fissures).

Gyration Index

• The gyration index quantifies the degree of folding by calculating the ratio of total cortical surface area to exposed cortical area.

• Gyration Index = \frac{Total Cortical Surface Area}{Exposed Cortical Area}

• Smooth brains, like those of rodents or manatees, have a gyration index around 1.

• Highly folded brains, like those of dolphins (cetaceans), have much larger gyration indices, with three times as much hidden cortex as exposed cortex.

• Carnivores have a gyration index of around 1.5 to 2, falling in the middle range.

• Human brains are more folded than chimpanzee brains, contributing to their larger size.

Determinants of Gyration

• Brain size is a major determinant of gyration, with larger brains tending to be more folded.

• Taxonomic affiliation also influences gyration; primates exhibit a steeper relationship between brain size and folding than carnivores.

• Cortical thickness affects gyration, with thinner cortices being easier to fold.

• The dominant theory suggests that cortical folding allows for packing more computational power into the skull.

• Cetacean brains have thinner cortices (around 1-1.2 mm) compared to many other mammals (around 2.5 mm), correlating with their highly gyrated brains.

Planes of Section

• Midsagittal Plane: Divides the brain into left and right halves.

• Sagittal (or Parasagittal) Plane: Parallel to the midsagittal plane, providing a side view of the brain.

• Coronal Plane: Cross-sectional or transverse plane, orthogonal to the sagittal plane, running from the front to the back of the brain.

• Horizontal Plane: Runs from top to bottom.

Brain Organization: Key Structures

• Telencephalon: the most rostral part of the brain, containing the cerebral hemispheres and basal ganglia.

• Diencephalon: contains the thalamus and hypothalamus.

• Mesencephalon: the midbrain.

• Pons and Cerebellum: the cerebellum is highly folded and contains a large number of neurons.

• Medulla: extends caudally, with a small portion connected to the spinal cord.

Brain Development: Neural Tube Formation

• The brain develops from a neural plate that folds to form a neural tube.

• The neural tube sinks beneath the surface of the skin; failure to do so leads to neural tube defects.

• The rostral end of the neural tube develops bulges that become the cerebral hemispheres and retinas.

• The walls of the neural tube contain cells that rapidly divide to form neurons and glial cells.

• Neurons: Responsible for computation.

• Glial Cells: maintain the metabolic and ionic environment of the neurons.

• The lumen inside the neural tube becomes the ventricular system, containing cerebrospinal fluid that is continually made and replenished.

• Blockages of the ventricular system can lead to hydrocephaly.

Brain Protection and Blood Supply

• The brain is protected by the skull, connective tissue, and skin.

• The meninges, three connective tissue layers (dura, arachnoid, and pia mater), surround the brain.

• Blood vessels supplying the brain travel underneath the dura and penetrate into the brain tissue.

• The meninges are composed of 3 layers: the dura, the arachnoid, and the pia mater.

White Matter and Gray Matter

• White matter appears white due to lipoproteins, primarily myelin, reflecting light.

• It consists of dense accumulations of nerve fibers (axons) that act as highways between brain regions.

• Gray matter contains neuron cell bodies, dendritic branches, and synapses, collectively called neuropil.

• Nucleus: A cluster of neuron cell bodies within the central nervous system.

Cellular Structure: Cerebral Cortex

• The cerebral cortex is organized into layers, traditionally labeled with Roman numerals.

• Layer organization reflects the inputs the cortex receives, with some inputs targeting specific layers.

• Neurons have branches, primarily dendrites, that receive synaptic inputs.

• A single neuron can receive thousands of synaptic inputs.

• Axons form an intricate pattern within the cortex, with vertical and horizontal trajectories.

• Neurons have dendritic branches covered in spines, which are extensions of the cytoplasm where most synapses are made.

• A single dendritic tree can have thousands of synapses.

Regional Brain Anatomy from Spinal Cord to Telencephalon

• The medulla and pons are part of the brainstem, controlling swallowing, coughing, breathing, heart rate, and taste, as well as basic motor programs for locomotion.

• The Pons contains:

  • Pontine Nuclei: Relays between the cerebral cortex and cerebellum

  • Reticular Formation: Organizes postural and motor locomotory patterns for motor control

• The cerebellum sits on top of the pons and medulla and has a cortex and deep cerebellar nuclei that communicate with other brain regions.

• Damage to the cerebellum can result in motor behavior alterations.

• The mesencephalon (midbrain) contains the periaqueductal gray, important for organizing stereotypic behaviors, red nucleus is a locomotor center.

• The diencephalon contains the hypothalamus and thalamus, the thalamus acts as the gateway to the cerebral cortex.

• The telencephalon is the frontmost portion of the brain containing the cerebral hemispheres.

Development of the Telencephalon

• Genes strongly influence gyration in mammals.

• Abnormal versions of genes (e.g., LIS1) can cause abnormal neuron migration, resulting in lissencephaly (smooth brain appearance), can also commonly cause seizure issues in dogs.

• Holoprosencephaly: A severe malformation involving incomplete bilateralization of the hemispheres. In it's most severs form presents as cyclopia.

Information Processing in the Brain and Cortical Maps

• Cortical maps organize information in the cortex, with primary sensory areas for vision (V1), audition (A1), and somatic sensation (S1), and primary motor cortex (M1).

• Cortex between primary areas is used for higher level function. Accessory visual function, or multimodal sensory areas

• Olfactory areas include the olfactory bulbs and piriform lobe.

• Dogs have a keen sense of smell aided by a large amount of olfactory receptive epithelium.

Olfaction (The Sense of Smell)

• Odorant molecules picked up in the nasal cavity by olfactory receptor neurons (ORNs) transmit information through the cribriform plate into the olfactory bulb.

• Dogs have approximately 200 million olfactory receptors with about 20,000,000 total, allowing them to have far better reception than humans with 4 to 5 square centimeters.

• The number of olfactory receptor proteins, ORNs, in the nasal mucosa has about 20,000,000 different cells.

• The dog versus human numbers of ORNs are about 20,000,000 versus about 20,000 (estimated). With 1,000 ORPs for each OCN, there's a lot of room to mix. So it's close to an infinite number of possibilities.

• The round portion of gray matter processing olfactory bulb information is the glomeruli.

• Each is receiving input from receptor neurons sent ot the mitral cells transmitting them to other parts of the brain.

• Odor molecules stimulate a unique pattern of responses with the receptor neurons stimulated to send their axons to the same glomerulus to create unique patterns.

• The olfactory bulb neurons send axons to the piriform cortex, olfactory cortex, and amygdala, as well as other brain areas to influence reproduction feeding, etc.

Vision (The Sense of Sight)

• The visual system starts in the retina, where neurons process the signals to be sent to the brain.

• Axons join the optic nerves which reach a point called the optic chiasm. In most mammals, about half of the axons cross to the other side.

• Meaning that brain regions processing information are dealing with information from both eyes.

• Visual information is then related to the visual thalamus by climbing up the optical tract to reach the lateral geniculate nucleus and into V1, the primary visual cortex.

• Genetic mutants can show abnormailites, for example Belgian sheepdogs can have an abnormal optic chiasm where there is no crossing causing functional issues.

• Visual information can be sent to non-cortical regions as well such as the pretectal area for capillary light reflexes and the rostral colliculus for visual startle reflexes.

• Some key structures in the visual pathway are: the tectospinal tract and the occulomotor nucleus.

Audition (The Sense of Hearing)

• Auditory processing regions begin in the inner ear being sent to brainstem and thalamus regions eventually reaching A1, the primary auditory cortex.

Somatic Sensation (The Sense of Touch)

• Somatic sensation involves touch, joint position, pain, and temperature.

• Spinal nerves provide sensory input from the caudal part of the body, while the trigeminal nerve processes from the head.

• Information is then passed to the thalamus through VCL and into the primary cortex S1.

• A map of the body is maintained throughout these processes.

• The proportion of representation of a part of the body is directly related to it's functional needs. For example touch receptors make up a platypus' bill, for which their map represents that part of the body most.

• Across mammals, varying degrees of the representation of touch occur dependent of lifestyle.

  • Visual areas are represented in the blue colors

  • Auditory in the yellow

  • the somatic sensory motor or somatic sensory area is in red.

Motor Side

• Three primary tracts influence motor outcomes.:
  * Corticopontine influences the cerebellum for fine motor control.
  * Corticobulbar affects brainstem and functions there chewing and digestion.
  * Corticospinal affects posture and locomotion.

Limbic System, Experience, and Amygdala

• The hippocampus is a C shaped structure is responsible for creating an enviornmental map as the animal moves around using neurons called place cells. It causes memories to then get transferred to the neocortex.

• Discriminative vs. Affective:
  * Discriminitive details exist around objective measures. (color, shape, etc.)
  * Affective involves how that thing or detail makes you feel

• The affective brain generates the behaviors linked to basic survival and well being. (Drinking, fighting, feeding, reproduction)

• Dopamine and the amygdala activate drive and pleasure with behavior. The nuecleus accumbens is activated to reinforce the drive. The amygdala triggers survival events and innate fear.

• The periaqueductal activation generates stereotypic behaviors such as vocalization and change in heart rate.

Canid Cognition

• Two main types of canid cognition will be emphasized here. Responding to human gestures, ad responding to human touch.

• Dogs quickly pick up signs from humans as to what actions they want them to perform. With a certain age of 3 weeks, puppies are willing to perform basic tasks for food rewards, like picking up a cup.

• Wolves are also capable of this function if they are hand-reared. Foxes are too if bred to not be aggressive.

• Shelter dogs also cannot perform said actions. Primates too cannot follow the gesture cues of humans. Social and non-social learning tests are therefore different.

• It is important to assess that canids possess these cues if treated and bred a certain way. Shelter dogs likely do not receive this information. Domestication and treatment for behavior is therefore an indicator.

• Oxytocin: Is released by both dog petter and the dog being petted to help form an important signal.

• The nervous system organizes perception and behavior.

• It coordinates sensory input and motor output.

• Topics include sensory systems, motor output, development, and dog brain comparisons.

• Examples of dog cognition related to human interactions will be discussed.

SIMPLIFIED

The Brain and Nervous System

• "Brain" refers to the entire nervous system.

• Peripheral nerves connect to the spinal cord and brain.

• Cranial nerves control vital functions unconsciously.

• Dog and wolf brains are similar at a gross level.

Mammalian Brains: Size and Gyration

• Brains vary in size and gyration (foldedness).

Brain Size vs. Body Size

• Brain size vs. body size shows a relationship with a slope of ~0.75.

• slope \approx 0.75

• Larger animals have relatively smaller brains.

• Human brains are larger than expected; dogs are typical.

Encephalization Quotient

• EQ = Observed brain size / Predicted brain size.

• EQ = \frac{Observed Brain Size}{Predicted Brain Size}

• Dogs have an EQ of ~1.0; humans ~7.0; manatees ~0.25.

Cerebral Hemisphere Gyration

• Brains have varying degrees of folding.

• Folding creates hidden cortex in sulci (fissures).

Gyration Index

• Gyration Index = Total cortical area / Exposed cortical area.

• Gyration Index = \frac{Total Cortical Surface Area}{Exposed Cortical Area}

• Smooth brains (rodents, manatees) have an index around 1.

• Folded brains (dolphins) have higher indices.

• Carnivores: 1.5-2; Humans > Chimpanzees.

Determinants of Gyration

• Brain size, taxonomic affiliation, and cortical thickness influence gyration.

• Folding allows more computational power in the skull.

• Cetaceans have thinner cortices.

Planes of Section

• Midsagittal: Left/right halves.

• Sagittal: Side view.

• Coronal: Front/back.

• Horizontal: Top/bottom.

Brain Organization: Key Structures

• Telencephalon: Cerebral hemispheres, basal ganglia.

• Diencephalon: Thalamus, hypothalamus.

• Mesencephalon: Midbrain.

• Pons and Cerebellum: Highly folded.

• Medulla: Connects to spinal cord.

Brain Development: Neural Tube Formation

• Neural plate folds into a neural tube.

• Tube defects occur if it fails to sink.

• Rostral end forms hemispheres and retinas.

• Walls form neurons and glial cells.

• Lumen becomes the ventricular system.

• Blockages cause hydrocephaly.

Brain Protection and Blood Supply

• Protected by skull, tissue, skin, and meninges (dura, arachnoid, pia mater).

• Blood vessels travel under the dura.

White Matter and Gray Matter

• White matter: Myelinated axons.

• Gray matter: Neuron cell bodies, dendrites, synapses (neuropil).

• Nucleus: Neuron cell body cluster in CNS.

Cellular Structure: Cerebral Cortex

• Cortex has layers.

• Neurons receive synaptic inputs via dendrites and spines.

Regional Brain Anatomy from Spinal Cord to Telencephalon

• Medulla/Pons: Brainstem, controls basic functions.

  • Pons contains:

  • Pontine Nuclei: Cerebral cortex & cerebellum relays

  • Reticular Formation: Posture & motor patterns organizer

• Cerebellum: Motor alterations with damage.

• Mesencephalon: Midbrain, contains periaqueductal gray, red nucleus.

• Diencephalon: Hypothalamus and thalamus.

• Telencephalon: Frontmost portion.

Development of the Telencephalon

• Genes affect gyration.

• Abnormal genes (LIS1) cause lissencephaly.

• Holoprosencephaly: Incomplete bilateralization.

Information Processing in the Brain and Cortical Maps

• Cortical maps organize information.

• Primary areas: V1 (vision), A1 (audition), S1 (somatic), M1 (motor).

• Olfactory areas: Bulbs and piriform lobe.

• Dogs have a keen sense of smell.

Olfaction (The Sense of Smell)

• Odorants bind to olfactory receptor neurons (ORNs).

• Dogs: ~200 million receptors.

• Humans: ~20,000 receptors.

• Glomeruli process olfactory bulb information.

• Olfactory bulb neurons project to piriform cortex, amygdala, etc.

Vision (The Sense of Sight)

• Visual system starts in the retina.

• Axons form optic nerves and chiasm.

• Information is relayed to the visual thalamus (lateral geniculate nucleus) and V1.

• Abnormal optic chiasm in Belgian sheepdogs.

• Visual information sent to pretectal area and rostral colliculus.

Audition (The Sense of Hearing)

• Begins in the inner ear.

• Projects to brainstem, thalamus, and A1.

Somatic Sensation (The Sense of Touch)

• Involves touch, joint position, pain, and temperature.

• Spinal nerves and trigeminal nerve.

• Information passes to thalamus (VCL) and S1.

• Body map maintained.

Motor Side

• Three primary tracts:

  • Corticopontine: Cerebellum (fine motor).

  • Corticobulbar: Brainstem (chewing, digestion).

  • Corticospinal: Posture, locomotion.

Limbic System, Experience, and Amygdala

• Hippocampus: Environmental map.

• Discriminative (objective) vs. Affective (feelings).

• Affective brain: Survival behaviors.

• Dopamine and amygdala activate drive/pleasure.

• Amygdala triggers survival/fear.

• Periaqueductal activation: Stereotypic behaviors.

Canid Cognition

• Responding to human gestures and touch.

• Dogs learn human cues for tasks.

• Wolves and foxes can learn with proper rearing.

• Shelter dogs may lack these cues.

• Oxytocin: Released during petting.