Behavioral Neuroscience, lecture on Lordosis Behavior
LORDOSIS
I. Behavior
A. Lordosis is a human medical disorder defined by an
excessive inward curve of the spine
1. This curve of the spine is also the main characteristic
of female sexual behavior in many species
a. rats are the most studied, but most quadripeds
and many bipeds show some variation of this
sexual position
B. Female Sexual Behavior
1. All sexual behavior necessary and sufficient to achieve
fertilization of ova by sperm
2. includes attractive, proceptive, receptive,
and copulatory behaviors
a. attractivity: stimulus value of a female
for a given male
b. proceptivity: extent to which females initiate
copulation
i. reflects overt behavior and
underlying motivational state
ii. females will not initiate proceptive behavior
with males to whom they are not attracted
(1) castrated males elicit fewer approaches
c. receptivity: state of responsiveness
to sexual initiation
3. Lordosis is a receptive and copulatory behavior
C. Proceptive Behaviors precede lordosis
1. but proceptive and receptive behavior overlaps
2. Proceptive behavior comprises all appetitve activities
a. sexually solicitous behavior
b. high levels of E2 faciliate proceptive behavior
3. Examples:
a. affiliative behaviors - maintaining proximity to males
b. assumption of mating posture
i. mounting by females (highly proceptive)
(1) thrusting
(a) may stimulate ovulation
c. presentation of genetalia
i. investigating male's genital region
d. specialized vocalizations
e. head bobbing
f. alternating approaches and withdrawals
4. Rats - Hopping and Darting
a. to initiate or maintaing mounting behavior by the male
i. solicitous behavior that the male finds attractive
(1) males are motivated to follow and mount
b. approach the male, then dart away
i. waiting
ii. run by
iii. return, pause in front of the male
c. hopping a short distance, wait, move back
d. wiggling the ears
D. Lordosis is a Reflex - in rats
1. stimulated by tactile sensory input of
male body against female's rump or flanks
a. female in estrous (heat)
i. estrous follows the follicular phase
ii. E2 levels are high,
followed by a short burst of P
iii. this reflex requires input from the brain
2. she will arch her back (curve spine)
a. deflect the tail
b. head is raised
c. stands completely immobile
3. precise postural adjustment
a. angle of genetalia
4. in the absence of lordosis, intromission and ejaculation
are impossible
E. Scoring Female responsiveness: Lordosis trials and success
1. Lordosis Scores (Hardy and Debold, 1971)
a. unreceptive (score 0: kicking, rearing, or fleeing)
i. back arched upward
b. proceptive (score 0.1 - 0.5)
c. receptive lordosis posture (scores 1-3)
with dorsiflexion of the vertebral column
i. 0.5 intervals,
depending on the degree of curvature of the spine
(1) 1 point: flat back, tail slightly raised
(2) 2 pts: back dorsiflexion, head flat
(3) 3 pts: severe dorsiflexion, head up
ii. score of 1 or higher considered lordosis response
for the calculation of lordosis quotient
2. Receptivity scores
a. average of 10 lordosis scores (0-3)
3. Lordosis Quotient (LQ)
a. ratio between male attempts and success
i. number lordosis/number mounts & intromissions
F. Reflexive Behaviors like Lordosis may be modified
1. hormones modify sexual behavior
a. receptors in the brain
2. input from limbic brain
a. enhanced by experience
b. diminished by stress
