Hemispheric laterality in animals and the effects of early experience

Abstract

A review of research with chicks, songbirds, rodents, and nonhuman primates indicates that the brain is lateralized for a number of behavioral functions. These findings can be understood in terms of three hypothetical brain processes derived from a brain model based on general systems theory: hemispheric activation, interhemispheric inhibition, and interhemispheric coupling.Left-hemisphere activation occurs in songbirds and nonhuman primates in response to salient auditory or visual input, or when a communicative output is required. The right hemisphere is activated in rats when spatial performance is required, and in chicks when they are placed in an emotion-provoking situation. In rats and chicks interhemispheric activation and inhibition occur when there is an affective component in the environment (novelty, aversive conditioning) or when an emotional response is emitted (copulation, attack, killing). An interhemispheric coupling (correlation) found in rats and rabbits implies that the hemispheres are two major components in a control system with a negative feedback loop. Early-experience variables in rats can induce laterality in a symmetric brain or facilitate its development in an already biased brain.It is predicted that functional lateralization, when present, will be similar across species: the left hemisphere will tend to be involved in communicative functions while the right hemisphere will respond to spatial and affective information; both hemispheres will often interact via activation-inhibition mechanisms when affective or emotional processes are involved. Homologous brain areas and their connecting callosal fibers must be intact at birth and must remain intact throughout development for lateralization to reach its maximum level. Injury to any portion of this unit will result in hemispheric redundancy rather than specialization. One major function of early experience is to provide stimulation during development, which acts to enhance the growth and development of the corpus callosum, thereby giving rise to a more specialized brain.

Influence of Naturally Occurring Variations in Maternal Care on Prepulse Inhibition of Acoustic Startle and the Medial Prefrontal Cortical Dopamine Response to Stress in Adult Rats

“…Early social isolation also results in decreases in basal DA turnover, selectively within the IL cortex (Heidbreder et al, 2000). Postnatal handling stimulates the development of cerebral lateralization (Denenberg, 1981;Denenberg et al, 1986). Interestingly, postnatal handling, which increases maternal licking and grooming (Lee and Williams, 1975;Liu et al, 1997), results in significantly reduced synaptic density in the IL cortex compared with nonhandled controls (Ovtscharoff and Braun, 2001), which may in part account for the reduced anxiety and high exploration typically displayed by neonatally handled animals.…”

“…Perhaps less well known is that the DA inputs to the left and right mPFC are functionally asymmetric, particularly with respect to stress responsivity (Slopsema et al, 1982;Carlson et al, 1991Carlson et al, , 1993Carlson et al, , 1996Sullivan and Szechtman, 1995;Sullivan and Gratton, 1998;Andersen and Teicher, 1999;Berridge et al, 1999;Thiel and Schwarting, 2001). Furthermore, the development of such hemispheric asymmetries in mPFC function can be altered by perinatal factors and the early postnatal rearing environment (Denenberg, 1981;Denenberg et al, 1986;Brake et al, 2000). These findings along with evidence derived from clinical observations have led to the suggestion that abnormal lateralization of mPFC DA-mediated function may increase the vulnerability to a range of stress-related psychopathologies (for review, see Sullivan and Gratton, 2002).…”

The Development of Postnatal Turning Bias is Influenced by Prenatal Visual Experience in Domestic Chicks (Gallus gallus)

“…To successfully hatch, the posture of the chick embryo must be oriented toward the top of the egg with the right side facing outward, thus providing a greater degree of mobility to the right side of the body (Oppenheim, 1972). This, in turn, provides more sensory and motor experience to the right side of the body, which appears to facilitate the development of hemispheriC lateralization and related behavioral asymmetry (see Denenberg, 1981, for a similar argument in mammalian species).…”

“…Individual turning bias indices were computed using a typical laterality formula (see Corballis, 1991;Denenberg, 1981). The formula produces a quantitative index for the direction of turning bias: (R -L)/(R + L).…”

Effort-Based Decision Making in the rat: An [18F]Fluorodeoxyglucose Micro Positron Emission Tomography Study

“…Lesions studies revealed that the rat brain shows a substantial hemispheric specialization (Denenberg, 1981;Sullivan, 2004). Furthermore, PET and fMRI imaging studies in humans demonstrated unilateral activations of prefrontal subregions .…”