What is the state of the brain when you are doing your best? When an animal is performing a task optimally? Here we address this question.
Does the cortex use a dense code in which neurons discharge to lots of stimuli (e.g. like a photoreceptor) or is the code more sparse, with spikes representing more rare events? A related question is: how energy efficient is the cortex? Do cortical neurons generate high rates of activity or are they more quiet than active? (A sparse code is typically associated with fewer spikes over prolonged periods.)
Here we used this system to address the questions - where do action potentials initiate in cerebellar Purkinje cells and do they propagate faithfully?
The synchronous activity of large numbers of neurons in the brain generates significant electric fields. These electric fields have been previously shown to influence pathological activity such as epileptic seizures.
Here we address the following questions:
- Where are action potentials initiated in cortical pyramidal cells? (Answer: axon initial segment!)
- How does intitiation of spikes in the axon influence the variability and reliability of spike intiation in these cells?
- How does initiation of spikes in the axon influence the appearance of spikes in the cell body and dendrite?
- What are the functional consequences of axonal initiation of action potentials?
The visual system calculates visual information through both brute force with millions of neurons, and through a number of short cuts, extrapolations, and self regulating mechanisms. These non-linearities in the visual system can be illustrated with visual illusions. Here, we will illustrate some of the features of the visual system that are related to those which we are currently investigating.
The pattern of activity generated by thalamocortical systems changes dramatically during different states of the nervous system, such as sleep,waking, and epileptic seizures. The presence of these changes in thalamocortical activity have been known for more than 100 years, owing to the pioneering work of an Englishman named Richard Caton (1887).
Traditionally, neurons in the brain are thought to collect information from other cells as an analog signal (voltage) that is generated by barrages of synaptic potentials. These synaptic potentials arise from the activity of thousands of inputs that each cell receives on its cell body and dendrites.
The brain is constantly active, even during deep sleep. In the cerebral cortex, this spontaneous activity (activity that is not obviously driven by a sensory input or a motor command) often occurs as periodic, rhythmic discharges.
The cerebral cortex exhibits multiple states of activity and excitability. Some of these states slowly change, such as the transition between sleep and waking. Others are more rapid, such as the operation of short-term or "working" memory and shifts in attention.
Neurons in the visual cortex are highly sensitive to local contrast, owing to the structure of their receptive fields (e.g. adjacent ON and OFF subregions).