CH 4 (2) - Neurons and the Brain Flashcards
(34 cards)
What does the cortical homunculus represent?
Illustrates how much space the sensory representations of different parts of the body occupy
in the cerebral cortex.
What does the Basal Ganglia do?
The basal ganglia are a group of nuclei (clusters of neurons) located beneath the cerebral cortex. The function of the basal ganglia is mainly related to the motor system where they are engaged in the planning, selection, execution and learning of actions.
What is the hippocampus?
sea horse like shape. it is involved in the formation of episodic long-term memories.
What is the function of the Amygdala?
group of nuclei related to the analysis of the emotional or motivational significance of stimuli.
What are the hippocampus and the amygdala parts of?
The limbic system
What three properties make the human brain stand out among other species?
- Neuron morphology
- Electrical properties of neurons
- Sequence processing
Neuron morphology of human brain
The pyramidal neurons in the human cortex have the most elaborate and spine-rich dendritic trees.
Electrical properties of neurons in the human brain
the pyramidal neurons in the human cortex have a very low membrane capacitance (storing of electric energy), which significantly enhances signal transmission.
Sequence processing in the human brain
Compared to other species, humans have superior capabilities of learning sequences of stimuli
When were neurons discovered?
in 19th century (1870s) by Golgi, Ramón and Cajal
When was the birth of artificial neural networks?
1943 when a computational model of the nervous system was developed.
- Every cell has only two states ( (firing and resting)
- A cell only fires if its input crosses a defined threshold
-> Starting point of modern AI
What is the perceptron and when was it developed?
1957: single neuron that can learn to classify input patterns.
- the neuron learns from falsely classifying samples by adapting its synaptic weights
When was the AI Winter?
- The perceptron only works for simple data sets that are linearly separable (Xor problem cannot be solved).
Why has the AI winter ended?
With the development of new neural network architectures and the back-propagation algorithm, which has become the basis of all modern neural networks architecture.
What are biological neurons?
Cells with a highly intricate structure and complex electrophysiological dynamics
What are analog neuron models?
real-valued (real numbers) output that can be interpreted as the neuron’s firing rate
( artificial neural network in which an electrically adjustable material is used to emulate the function of a neural synapse.)
spiking neural network
emits impulses that correspond to the spikes emitted by biological neurons
Analog neuron model forumla
output = n(x) = A(w1x1 + … + wnxn + b)
Common activation functions
Binary step function Logistic function tanh Rectified Linear Unit (ReLu) Exponential Linear Unit (ELU) Gaussian
What is information processing in biological neurons largely driven by?
ionic currents that accumulate in the soma (cell body)
How can the flow of the currents in the soma be modeled?
functionally equivalent electrical circuits
What is the Leaky Integrate-and-Fire Model?
first spiking neuron model that is still of relevance today. Comprises of a electric circuit composed of resistors and capacitors. It may be driven by a voltage or current source and these will produce different responses.
Does the LIF neuron capture cell morphology?
No it is a point neuron model?
More detailed spiking neuron models are derived from the
Hodgkin-Huxley model
