CHAPTER 12(omit developmental section) CHAPTER 13 (omit heart/brain and conditioning sections) Also see Chapter 18 sections on Orienting and Defensive responses.

I.Electrocardiogram (EKG or ECG) - electrical potentials associated with neural activation and rhythmic contraction of the atria and ventricles of the heart .

A. The electrical cardiac cycle: PQRST (see Figure 11-1)

1.P-wave: onset marks the excitation of the sino-atrial node, duration marks the depolarization of the atria.

2.Q-wave: onset marks the depolarization of the atrial-ventricular node, minimum marks the onset of depolarization of the ventricles.

3.R to S-waves: depolarization of the ventricles.

4. T-wave: repolarization of the ventricles.

II.Impedance Cardiogram (ZKG) - electrical impedance changes associated with change in blood volume ejected into the aorta from the left ventricle.

A.The impedance cardiac cyclic: the first derivative of impedance change (Z) against time (t) or dZ/dt (see Figure 11-1)

1. B point - time when the aortic valve opens

2. Zmax - peak blood flow (corresponds to systolic blood pressure)

3. X point - time when the aortic valve closes.

III. Common cardiac measures (see Figure 11-1)

A. Chronotropic - measures of time between events in cardiac cycle.

1. Heart rate (HR) - number of heart beats per minute (BPM).

2.Heart period (HP) - time (in ms) between successive R-waves (R-R interval or interbeat interval (IBI)). This measure is currently preferred for research purposes because it represents the physical unit of change, and because it has superior statistical properties.

HR = 60,000 / HP (in ms)

B.Inotropic - measures of contractile force. The measures below are really chronotropic, but more forceful ventricular contractions take less time.

1.Pre-ejection period (PEP) - time from onset of the EKG Q-wave (electrical depolarization of the ventricles) to the ZKG B point (opening of aortic valve and onset of ejection of blood from the left ventricle). Shorter PEP with more forceful ventricular contractions. PEP is a very important measure because it is determined solely by sympathetic neurogenic activity: sympathetic activation results in shorter PEP, sympathetic inhibition results in longer PEP.

2.Left ventricular ejection time (LVET) - time from the ZKG B point (opening of aortic valve) to the ZKG X point (closing of aortic valve). Shorter LVET with more forceful ventricular contractions.

C.Heart rate variability (HRV) - measures of homeostatic mechanisms associated with temperature, blood pressure, and respiration. These variations are NOT merely the statistical variance (e.g., s2), but are rhythmic variations in heart rate (or period) that take place over a period of minutes at specific frequencies. This variability is often quantified with FFT in the same way that EEG is, except at much lower frequencies. The two components that we mentioned are often called low and high frequency HRV.

1.Low frequency HRV - occurs at around 0.1 Hz and is associated with feedback loops that maintain blood pressure.

2.High frequency HRV - occurs at respiration frequency, usually around 0.15 to 0.4 Hz for adults at rest. This component is also called respiratory sinus ahrrthymia (RSA). Remember that the heart and lungs are both innervated by the Xth cranial nerve (the vagus). HR increases with inspirations and decreases with expirations so that variability in heart rate at the respiration frequency indicates vagal parasympathetic activity. RSA is a very important measure because it is determined solely by parasympathetic neurogenic activity: parasympathetic activation results in increased RSA, parasympathetic inhibition results in decreased RSA.

D. Tonic vs Phasic distinction.

1.Tonic - change that takes place over an extended period of time, usually minutes (like EEG only over longer time) such as HR, HP, HRV

2.Phasic - event-related (evoked) change that takes place over a short period of time, usually seconds (like ERP only over longer time)

a. Phasic response usually shown as change from prestimulus baseline

b. Phasic response usuallyconsists of three components (see figure below)

i. initial deceleration (D1) often thought to reflect orienting to the first stimulus (S1).

ii. acceleration (A) often thought to reflect processing of the first stimulus (S1). Defensive response will have a large A component and no D1 component.

iii. second deceleration (D2) often thought to reflect preparation for the second stimulus (S2).

IV. Autonomic Determinism (Bernston, Cacioppo, & Quigley, 1991)

A. Autonomic Space

1.Principle of multiple modes - sympathetic and parasympathetic neurogenic inputs to the heart can occur in a number of ways in response to psychologically significant tasks, not just in the reciprocally-coupled ways that are observed during physiologically significant tasks.

Table 7
Possible Modes of Autonomic Control for Heart Rate

B.Knowledge of the underlying sympathetic and parasympathetic activity during performance of a task may result in a greater understanding of the brain activity that produces a given HR change. This knowledge of the underlying sympathetic and parasympathetic activity is usually obtained in psychophysiological studies from PEP and RSA.

V.Summary of Backs et al. studies that measured HP, PEP, and RSA during a variety of tasks.

A.Psychomotor tasks like manual tracking that result in shorter HP (i.e., faster HR) during the task than during baseline seem to elicit uncoupled parasympathetic withdrawal. Increasing task difficulty such as increasing motor response processing seems to elicit greater uncoupled parasympathetic withdrawal.

B.Cognitive tasks such as mental arithmetic and the QRST memory task that result in shorter HP (i.e., faster HR) during the task than during baseline seem to elicit reciprocally-coupled sympathetic activation and parasympathetic inhibition. However, increasing task difficulty such as increasing problem difficulty or memory load seem to elicit uncoupled sympathetic activation.

C.The high mental workload condition in the flight simulation study that resulted in shorter HP (i.e., faster HR)than during the low mental workload condition seemed to elicit uncoupled sympathetic activation.