Motivation

Kun-Ruey Shieh, Ph.D.謝坤叡Inst. of Neuroscience

D807, Ext. 7138/7389

Rationale

Behavior has two aspects to reflect; one is with cognitive, and the other is non-cognitive.

The latter one is the domain of motivation- or called the drive states.

Motivational states may be broadly classified into two types: (1) brought by alterations in internal physical conditions, and (2) personal or social aspirations acquired by experience.

Driving States are simple cases of motivational states that can be modeled

as servo-control systems

Set point, error signal

Temperature regulation involves integration of autonomic, endocrine, and skeletom

otor responses

The detectors of temperature have two parts; one is peripheral and located throughout the body, and the other is central and located in the anterior hypothalamus.

The mediator of temperature also have two parts; the anterior hypothalamus mediates decreases, and the posterior hypothalamus mediates increases in body temperature.

Posterior (posterolateral) hypothalamus

Anterior (anteromedial) hypothalamus

Fever

(IL-1, IL-6, TNF)

AspirinIndomethacin

Feeding behavior is regulated by a variety of mechanisms

The reason for thinking that feeding behavior is subject to a control system is that body weight seems to be regulated by a set point.

Animals often maintain the same body weight for a long period.

However, this set point can vary with stress, palatability of food, exercise, and many other environmental and genetic factors.

Dual controlling elements in the hypothalamus contribute to the control of food intake

Tg-Agouti

Normal

Other factors in hypothalamus related to feeding

Amphetamine, CCK, calcitonin, leptin: decreased the appetite

Orexin, neuropeptide Y: induced the appetite

The effects of hypothalamic lesion in feeding are thought to be due in parts of :

1. Alteration of sensory information,

2. Alteration of set point

3. Interference with behavioral arousal.

1. The destruction of trigeminal system and DAergic fibers of the medial forebrain bundle.

2. Fig. 51-5.

3. Damaged the pathways from the SNc to the ST, and from the VTA to the limbic systems (including the prefrontal cortex, amygdala, & NA).

Thirst

Drinking is regulated by plasma osmolality & extracellular fluid volume (ECF).

Osmoreceptors are located in the anterior hypothalamus.

• Subfornical organ

• Organum vasculosum of the lamina terminalis (OVLT)

OVLTPI

NH

ME

SCO

SFO

CP

AP

Thirst

Relation to Sympathetic Response

Stimulation of lateral part of hypothalamusBP increasePupillary dilationPiloerection

Stimulation of middorsal partVasodilation in muscle & vasocontriction in skin

Hypothalamus is called the cholinergic sympathetic vasodilator system.

Stimulation of dorsomedial & posterior part Secretion of Epi & NE increased from Adrenal medulla

Relation to Sleep

Lesions of posterior hypothalamus caused prolonged sleep

Stimulation of dorsal part in conscious animals caused their sleep

• However, these experiments might block or stimulate the reticular activating system (RAS) in the brain stem as their fibers passed to the thalamus & cortex

Mutations in single genes can affect certain behaviors in flies

Drosophila

Period (per) & timeless (tim) genes --- circadian rhythm

Mice

SCN

Clock mutation23.1 h

24.9 h

28.4 h

Motivational states can be regulated by factors other than tissue needs

Ecological constraints- evolutionary selection

Anticipatory mechanisms- intrinsic circadian clock

Hedonic factors-