Lecture 10 - Cortical Maps and Plasticity Flashcards
What is a map in the context of neuroscience?
- A map is a representation. “The map is not the territory it represents, but, if correct, it has a similar structure to the territory, which accounts for its usefulness.” Alfred Korzybski (1931)
- This map can represent various aspects, including sensory information and brain areas
What are primary sensory areas and their significance?
- Primary sensory areas are the first cortical regions to receive sensory information from sensory senses
- They are often the starting point for mapping sensory inputs in the brain
How does the rodent whisker system serve as a model for sensory maps?
- Rodents use their whiskers to explore the environment, building a 3D map without visual input
- The barrel cortex in rodents maps spatial organisation of whiskers, with each whisker represented by a cluster of cells that respond to specific whisker stimulation
- This is crucial for plasticity studies and understanding brain mapping
What is the role of the barrel cortex in rodents?
- The barrel cortex represents the spatial organisation of the whiskers
- Each barrel is a group of cells that responds to a specific whisker
- This system helps track sensory information from the whiskers as the rodent explores
What did Hubel and Wiesel contribute to modern neuroscience?
Hubel and Wiesel pioneered the study of sensory maps, particularly investigating the selectivity of cell responses, and laid the foundation for understanding neural physiology
What is a retinotopic map, and where is it found?
- A retinotopic map represents visual space
- It has neurons in the lateral geniculate nucleus (LGN) and primary visual cortex (V1) responding to different areas of the retina
- It helps process visual input based on the spatial location in the visual field
Why is the fovea represented more richly in the brain?
The fovea, which contains the highest density of photoreceptors, is disproportionately represented in the visual cortex due to its high bandwidth of information, resulting in cortical magnification of the fovea
What are photoreceptors and their types?
- Photoreceptors convert light into electrical signals
- Rods: Night vision, black-and-white, sensitive to light, located in the retina’s periphery
- Cones: Colour vision, fine detail, work in bright light, found mainly in the fovea
What are orientation preference maps in V1?
- Orientation preference maps show how neurons in V1 respond more strongly to specific orientations of stimuli, such as vertical or horizontal lines
- This is studied using tuning curves and helps understand how visual stimuli are processed
What is a receptive field of a neuron?
- A receptive field is the specific region of sensory space (e.g., a particular whisker or a line’s orientation) that excites a neuron the most
- This is crucial for sensory processing and creating maps of sensory input
What are mechanoreceptors, and their function?
- Mechanoreceptors are sensory receptors that respond to mechanical changes, such as touch or vibration
- They include Meissner corpuscles (dynamic deformation), Pacinian corpuscles (vibration), Merkel cells (indentation depth), and Ruffini corpuscles (stretch)
What is the dorsal column pathway, and what is its role?
- The dorsal column pathway transmits fine touch information from the body to the brain
- It includes afferents (Gracile and Cuneate fasciculi) and synapses in the thalamus, where information is relayed to the primary somatosensory cortex (S1)
What is somatotopic organisation?
Somatotopic organisation refers to the mapping of the body on the brain’s surface, where the right side of the body is represented in the left hemisphere, and vice versa, with multiple maps for fine motor and sensory functions
What did the 1984 study on plasticity after peripheral trauma show?
- It demonstrated that changes in sensory input, such as amputation, could alter the structure of cortical maps
- In adult animals, the amputated zone’s receptive field in S1 was now driven by adjacent areas, showing that the brain’s sensory maps are adaptable
What did the 1988 study on use-dependent change in monkeys reveal?
- It showed that experimentally joining two fingers in monkeys (syndactyly) led to the development of new, dual receptive fields at the border of the two digit’s cortical representations
- This demonstrated the brain’s ability to adapt to changes in sensory input
What is the concept of critical periods in brain plasticity?
- Critical periods refer to specific developmental windows when sensory experiences have a profound effect on brain organisation
- E.g., In visual development, exposure to certain stimuli during critical periods shapes sensory processing areas like V1
What was Colin Blakemore’s (1970s) experiment with kittens, and what did it demonstrate?
- Blakemore raised kittens in an environment with only vertical or horizontal lines
- Shows that sensory input during the critical period could shape the orientation specificity of neurons in V1
- This is because after exposure to only vertical lines, the kittens showed no response to horizontal lines in their visual cortex
Can the brain continue to adapt after the critical period? (Give details)
- Yes, although the brain retains plasticity post-critical period, the ability to reorganise and form new maps diminishes with age
- Post-critical period adaptions involve more complex stimuli processing, such as face-selective cells
What role do mechanoreceptors play in somatosensory processing?
- Mechanoreceptors are crucial for detecting tactile sensations, such as pressure, vibration, and texture
- These receptors, like Meissner, Pacinian, Merkel, and Ruffini, provide the brain with detailed information about the environment
What did the 1978 study on somatosensory map plasticity in monkeys (primates) reveal?
- This study demonstrated that primate brains have two topographic maps of the body with cytoarchitectonic areas 3b and 1
- Also showed that these maps show fine details in terms of body surface representation
How is the body mapped in the brain?
- The body is mapped in the brain in a somatotopic fashion, where the right side of the body is represented in the left hemisphere, and vice versa
- This map helps to process fine touch and proprioception
