Neurovascular Coupling

Question 1

Rees, Friston, Koch (2000)

Answer 1

• These findings suggest that BOLD contrast is directly proportional to the average neuronal firing rate, consistent with recent suggestions

Question 2

What is neurovascular coupling?

Answer 2

The mechanism that links the vascular (fMRI) signal to neural activity
 BOLD is mostly a vascular signal
BOLD - Depends on the concentration of deoxyhemoglobin -> combination of cerebral blood flow (CBF) and energy use
- BOLD signal originates because blood flow increases more than energy use, resulting in an inflow of fresh blood, and a net dHb decrease, hence a signal increase
 meets metabolic demands and is driven by neurotransmitter release

Question 3

what increases the increase in blood flow?

Answer 3

 neural activity results in increased energy consumption (increased metabolism) and increased blood flow, which leads to BOLD -> but the blood flow increase is preemptive (präventiv)

• Preemptive signaling: neurotransmitters released by neural activity triggers vasodilation
• Neurotransmitters give signals to increase blood flow
• Neural activity -> neurotransmission -> blood flow & volume -> blood oxygenation -> BOLD signal

Question 4

What kind of neural activity drives the BOLD signal?

Answer 4

• The neurophysiological response is faster and precedes the hemodynamic response
• LFP is better correlated with the BOLD-signal than spikes, in cases where LFP and spiking activity are “dissociated”
   Neurotransmission, increase in perfusion (Durchblutung) in anticipation of energy consumption
• Synaptic activity > spiking (neuronal spiking is not required for fMRI signals; Viswanathan, Freeman)  synaptic activity often better correlated than spiking activity

Question 5

Negative BOLD

Answer 5

• If the control task has a higher activation than the task of interest (although both responses are positive) you will get a negative response