Lateralization of functions in the vertebrate brain: A review

Abstract

That the human left and right cerebral hemispheres perform different functions is widely accepted; but there is little evidence of whether or not similar functional asymmetries exist in non-human vertebrates. In this paper, neuro-anatomical similarities between human and other vertebrate brains are considered, and data concerning physical asymmetries reviewed. The defining features of human lateralization are taken to be right-handedness, as a skewed but continuous distribution of preferences, and a greater involvement of the left hemisphere in species-specific vocalization, with right-hemisphere superiority in spatial perception and emotionality less well-marked characteristics. Rodents, cats, at least one species of marsupial, and macaque monkeys have consistent hand preferences for food reaching. These may result from constitutional factors, but in every species studied the distribution of preferences is unskewed. Canaries appear to have left-hemisphere dominance of vocal production, and there is limited support for the conjecture that macaque monkeys have left-hemisphere dominance for reception of species-specific cries, and/or for short-term auditory memory. Left and right unilateral hemispheric damage may have appreciably different effects on emotionality in rats, sound localization in cats, and tactile discrimination in monkeys, although the available evidence is equivocal. It seems possible that asymmetries of cerebral function are widespread in vertebrates. In particular, left hemisphere dominance of species-specific communication might be common in birds and primates: left-hemisphere dominance of human speech may be an example of a general vertebrate tendency towards unilateral control of vocalization.

Right ear advantage for vocal communication in frogs results from both structural asymmetry and attention modulation

“…Since projections to the midbrain arise primarily from the contralateral auditory periphery, the results obtained here support the hypothesis that right-ear/left-hemispheric superiority for processing communication sounds in frogs is to a significant extent due to structural asymmetries in the way the auditory system processes information. This finding is also in agreement with earlier studies on REA in amniote vertebrates holding a left-hemisphere priority for processing conspecific/neighbor vocalizations [1,[16][17][18][19]24,[52][53][54][55][56][57]. Furthermore, the REA in music frogs has been demonstrated, at least in part, in a preliminary behavioral study using a head orienting task in which the subjects preferentially turned their bodies toward the right while listening to HSA playbacks, but did not show a turning preference in silence (unpublished data).…”

Concordance of handedness between teacher and student facilitates learning manual skills

“…Pre-hominids were probably evenly distributed in their handedness (Annett, 1978;Walker, 1980). As toolworking skills evolved as an important component of hominid evolution, the social transmission of these skills would have depended on observational learning.…”

Asymmetrical turning during spermatophore transfer in the male smooth newt

“…However, it has often been proposed that limb laterality occurs only when limbs are used for manipulative activities such as feeding or handling objects (Walker 1980;Gü ntü rkun et al 1988). Male newts do not use their limbs for manipulating objects.…”