Section B: Cellular basis of Cognition . 25% of exam mark. Allow 45 mins.
Write an essay that addresses the following two questions. Refer to material discussed in lectures, including specific experiments, to support your answers.
1) What is a spatial cognitive map? How is it thought to be represented in the
ain? What is the evidence for and against the existence of spatial maps? (50% of this section)
2) What factor(s) potentially distinguish spatial maps from memory based cognitive maps? Are they truly different? Can they be reconciled and if so, how? (50% of this section)
Section C: Molecular . 25% of exam mark. Allow 45 mins.
Discuss amyotrophic lateral sclerosis (ALS) as an example of a slow neurodegenerative disease.
· List very
iefly the main characteristics of the disease (onset, course, symptoms and prognosis) (25% of marks for this section)
· What are the main pathological findings at the cellular and molecular level? (25% of marks for this section)
· How could the changes in cells and molecules observed in ALS relate to the mechanisms of the ALS-related neurodegeneration? (25% of marks for this section)
· In terms of cellular and molecular mechanisms, how would you best approach the quest for an effective treatment/cure/prevention of ALS? (25% of marks for this section)
2
Cellular Basis for Cognition
Cellular basis for cognition: introduction (appreciate the concepts here)
Introduce terms, concepts and methods that will allow us to discuss topics relating to cognition.
• Cognition is the process by which we acquire and comprehend information through experiences and
actions, ultimately resulting in us successfully negotiating our external world.
• It includes specific concepts including:
o Perception and representation –
Interpret sensory information that is bombarding us; the ability to become aware
through the senses.
Generate a representation that allows us to immediately comprehend what is “out
there” and also aspects of ourselves.
o Learning and memory –
Forming associations between certain features and actions also creates
epresentations that can be stored and retrieved from memory.
Storage of representations allows us to predict and plan future actions based on
these representations formed from sensory input.
Learning, memory and representation are inte
elated on a conceptual level.
o Deliberation and decisions –
By retrieving information from the past and taking onboard what is happening now,
we can evaluate and make choices.
Appreciate that there are different levels of elements and organization within the
ain.
• A cartoon drawing of a pyramidal neuron, an active cell present in our
ain. When discussing neural
activation or functioning of the
ain, the information usually comes from data recordings from
individual neurons.
• However, we know that individual neurons act as parts of circuits or networks of cells.
o Circuits can be considered as interconnected neurons that are present locally,
o whereas networks are across different areas of the
ain/nervous system.
Appreciate that there are many ways of assessing
ain function.
Concepts: Levels
• What will we be measuring to assess function? There are different levels at which we can investigate
the cellular processes underlying complex functions such as cognition.
1. At the most basic level (individual cell), we can study synaptic transmission – how do individual cells
communicate with each other?
o Recordings of individual neurons allows us to isolate excitatory and inhibitory inputs to cells,
thus allowing us to assess how cells receive information.
o We can examine how manipulating cell communication at a synaptic level can change the
eliability/efficacy of information transfer.
2. We can also consider neural activity – how are neurons responding to different stimulus in order to
elicit neural activation?
o An invasive procedure that requires sticking electrodes in a particular
ain area allows
extracellular recordings of activity to be taken.
Little stripes co
espond to AP firing
from individual cells.
Upon presentation of a fixation
point/stimulus, the cell consistently fires
more APs.
Histogram shows overall distribution of
number of APs generated per unit time;
informs us that the cell is particularly
esponsive to that shape.
Neuronal activity reflects its selectivity for a particular visual object. Allows us to
appreciate that certain areas of the
ain are perceptive to certain stimuli.
o APs are a proxy of that cell’s output; if a downstream cell fires an AP, then in some way it
suggests that the upstream cell was successful in conveying information downstream.
o Synaptic activity is integrated both temporally and spatially – this results, in a probabilistic
fashion, cells generating an action potential.
3. Non-invasive methods to image activity (e.g. EEGs) allow us to look at network activity, which is
activity across various regions of the
ain.
Concepts: Features
• Certain features of cellular activity reflect the things that an organism is engaging in.
• Receptive fields pertain to how we generate a representation of the external world.
o E.g. a particular cell in the visual cortex is particularly sensitive to stimulation from a certain
portion of the visual field. That specific location is the receptive field for that cell.
• Engrams are a cellular manifestation of memories. They are a hypothetical permanent change in the
ain which accounts for the existence of memory.
• States are also related to memories.
Concepts: Organisation
• Connectivity – pattern of anatomical links, statistical dependencies or
causal interactions between distinct units within the
ain.
o Appreciating the type of information that a neuron receives and
where it is coming from allows us to appreciate functional
connectivity.
o Important for appreciating the organisation of input from individual
neurons.
o E.g. where cells across different layers of the multilayered visual
cortex are projecting to and providing their excitatory synaptic
connections with individual cells.
• Topography – sets of neuronal connections preserve the relative organisation of cells between two
egions; ordered projection of a sensory surface to the CNS.
o E.g. cortex is a sheet with topographical structure. Different areas of cortex are being driven
y a different type of stimulus.
o While presenting stimulus to an anaesthetised animal, they injected a
metabolic marker.
After anatomically analysing the visual cortex, they found that
there was a 1:1 co
espondence between what was activated at
the level of the retina and what was seen in V1.
Some features of the visual stimulus were clearly observed in
the activation patterns within V1 – radial rings and radii are
matching.
However, spacing between rings is different. This may indicate
an ove
epresentation of foveal information (i.e. overallocation
of cortical real estate to analysing foveal information).
• Transformations – our visual world is not limited to what is in front of our face,
instead we have a continuous appreciation of everything out there. (See next section.)
o For this to happen, there needs to be a transformation from the retinotopic reference frame
to another reference frame (e.g. something that also takes on vestibular input).
o E.g. where the animal is gazing (gaze angle) affects the way a cell responds when you
stimulate its retinotopically mapped receptive field – consider the rate at which it fires.
If the receptive field of the cell in this higher order visual area was only dependent on
visual stimulation, then regardless of where the animal is gazing, the same stimulation
should lead to the same response.
However, depending on where the animal is looking, the response changes, meaning
that cell must be receiving some other information in order to modulate its activity.
Perhaps, vestibular or motor input is also influencing responsiveness.
Proprioceptive influences affecting perception.
Become familiar with some of the primary functions of the
ain. How are they related?
• Transmission and transformations.
o One of the main functions of circuits is to transmit information via synaptic communication.
o However, this information is taken up and transformed such that subsequent targets of this
cell receive different information to digest.
o E.g. retinal ganglion cells have a concentric receptive field.
However, if we record simultaneously from a cell in the LGN that was
esponsive to the presentation of a stimulus in a particular portion of
the visual field and also record from an individual neuron within the
primary visual cortex that had an overlapping receptive field, we see
that the concentric circle contributes to the formation of a slightly
different receptive field.
LGN is providing information and contributes to a transformation of the receptive
field shape from concentric to something that is orientation selective.
o E.g. when looking at awake-behaving subjects and considering higher up visual hierarchical
areas, we begin seeing cells that become responsive to much more complex structures.
Infratemporal cortex (higher level area within ventral
processing stream), cells become particularly sensitive
to face-like structures.
As we go into higher order visual processing areas,
there are successive transformations of information
(and essentially consolidation of information) that
allow us to form complex representations with higher
order features.
• Representations.
• Learning and memory (acquisition and storage), choice.
o Transformations are involved in forming associations. Confluence of input can lead to
downstream targets receiving weighted input that leads to the formation of more reliable
transmissions of information – cellular underpinning of learning.
If we learn something, we form an association that can be stored – becomes memory.
If we can retrieve that memory, we can then act upon it. Also gives us choice.
E.g. rats can be trained to form associations and we can then assess the neural
processes it is engaging in by considering how they behave.
Specialisation
• Different species have
ains that have evolved to become specialised for their particular ecological
niche. Primate and murine visual systems are different and serve different functions for survival.
o E.g. mice are afraid of predators.
Stimuli that emulates the a
ival of an aerial predator can elicit a dramatic response. If
we present a circle that rapidly expands overhead on top of the animal, the animal
will notice this object and flee immediately into shelter.
o When studying different systems, we should think about what the species “cares” about –