Part two of this three-part series commences with anomalous dominance and special talents. Part one appears in a previous issue of theArchives. 1 ANOMALOUS DOMINANCE AND SPECIAL TALENTS According to our hypothesis, slowed growth within certain zones of the left hemisphere is likely to result in enlargement of other cortical regions, in particular, the homologous contralateral area, but also adjacent unfaffected regions. The influences that favor anomalous dominance may thus favor talents associated with superior development of certain regions either in the right hemisphere or in adjacent parts of the left hemisphere. Even with excessive retardation of growth and the resultant migration abnormalities and learning disorders (LD), high talents may exist as a result of compensatory enlargement of other cortical regions. Several types of data are in concordance with these conclusions. Several studies have claimed that the average level of spatial talents is higher in male subiects. 2 Hier

https://jamanetwork.com/journals/jamaneurology/articlepdf/584161/archneur_42_5_008.pdf

Cerebral lateralization. Biological mechanisms, associations, and pathology: II. A hypothesis and a program for research.

Dual functional brain asymmetry refers to the notion that in most individuals the left cerebral hemisphere is specialized for language functions, whereas the right cerebral hemisphere is more important than the left for the perception, construction, and recall of stimuli that are difficult to verbalize. In the last twenty years there have been scattered reports of sex differences in degree of hemispheric specialization. This review provides a critical framework within which two related topics are discussed: Do meaningful sex differences in verbal or spatial cerebral lateralization exist? and, if so, Is the brain of one sex more symmetrically organized than the other? Data gathered on right-handed adults are examined from clinical studies of patients with unilateral brain lesions; from dichotic listening, tachistoscopic, and sensorimotor studies of functional asymmetries in non-brain-damaged subjects; from anatomical and electrophysiological investigations, as well as from the developmental literature. Retrospective and descriptive findings predominate over prospective and experimental methodologies. Nevertheless, there is an impressive accummulation of evidence suggesting that the male brain may be more asymmetrically organized than the female brain, both for verbal and nonverbal functions. These trends are rarely found in childhood but are often significant in the mature organism.

Sex differences in human brain asymmetry: a critical survey

A stereotaxic atlas of the rat brain

The hypothesis that separate neural systems mediate the reinforcing properties of opioid and psychomotor stimulant drugs was tested by examining the role of mesolimbic dopamine (DA) neurons in maintaining intravenous heroin and cocaine self-administration. After local destruction of the DA terminals in the nucleus accumbens (NAcc) with 6-hydroxydopamine (6-OHDA), rats trained to self-administer cocaine and heroin on alternate days were observed for changes in their drug-seeking behaviors. Postlesion responding for cocaine showed a time-dependent decrease or extinction, whereas heroin self-administration showed a time-dependent recovery. By the fifth trial postlesion, heroin self-administration had recovered to 76% of prelesion baseline levels, but cocaine self-administration had dropped to 30% of prelesion baseline rates. Thus, selective lesions of the DA terminals in the nucleus accumbens significantly attenuate cocaine but not heroin self-administration. These data support the hypothesis that independent neural substrates are responsible for the reinforcing actions of these two drugs.

Destruction of dopamine in the nucleus accumbens selectively attenuates cocaine but not heroin self-administration in rats

The hypothesis that separate neural systems mediate the reinforcing properties of opiate and psychomotor stimulant drugs was tested in rats trained to lever-press for IV injections of either cocaine or heroin during daily 3-h sessions. Pretreatment with the opiate receptor antagonist drug naltrexone produced dose-dependent increases in heroin self-administration, but had no effect on the rate or pattern of cocaine self-administration. Similarly, pretreatment with low doses of the dopamine antagonist drug alpha-flupenthixol produced dose-dependent increases in cocaine but not heroin self-administration. High doses of alpha-flupenthixol eliminated all responding for cocaine and slightly reduced heroin self-administration. The specificity with which the two antagonist drugs exerted their behavioral effects strongly suggests that independent neural substrates are responsible for the reinforcing actions of heroind and cocaine.

Heroin and cocaine intravenous self-administration in rats: Mediation by separate neural systems

Nocturnal rotation in normal rats: Correlation with amphetamine-induced rotation and effects of nigro-striatal lesions

Rats were trained to bar press on a differential-reinformcement-of-low-rate 16-sec (DRL 16) schedule for water reinforcement. On alternate days, rats were tested in the presence or absence of a light that signaled the availability of reinforcement. Rats were allowed to bar press on either of two levers (left and right). All rats showed consistent side preferences. For the non-signaled condition but not for the signaled condition, normal baseline rates were related to the strength of side preferences; lower rates and better timing performance were significantly correlated with greater preferences. Unilateral lesions in the caudate nucleus ipsilateral to side preferences facilitated timing performance during nonsignaled test sessions and increased side preferences during both nonsignaled and signaled sessions. Unilateral caudate lesions contralateral to side preferences impaired timing performance during nonsignaled test sessions and decreased side preferences during all sessions. Bilateral caudate lesions transiently depressed response rates without significantly affecting timing performance or side preferences. It is suggested that side preferences are intimately involved in the control of behavior by internal stimuli and that an inherent asymmetry in nigrostriatal function underlies side preferences; the effect of a unilateral striatal lesion will depend upon whether the lesion is placed in the more or less active striatum.

Differential effects of unilateral and bilateral caudate lesions on side preferences and timing behavior in rats.

Relationship of rats' spatial preferences effects of d-amphetamine on timing behavior

Rats were trained to bar-press for intravenous infusions of morphine sulfate during 1-h daily test sessions. Rates of morphine self-administration were enhanced by lesions of the frontal cortex and hippocampus and transiently reduced by lesions of the medial forebrain bundle and medial thalamus. Dose-response studies indicated that sensitivity to morphine's rewarding property was decreased by frontal cortical and hippocampal lesions. Lesions of the posterior cortex, the tuberculum olfactorium, and the nucleus accumbens had no effect on self-administration behavior. The results are discussed in relation to previous findings with caudate and brainstem lesions. A neuroanatomical substrate for morphine reinforcement is suggested.

Changes in morphine self-administration after tel-diencephalic lesions in rats.

Rats were trained to bar press for intravenous infusions of morphine sulfate during 1-h daily test sessions. Rates of morphine self-administration were reduced by bilateral lesions of the substantia nigra and enhanced by lesions of the medial raphe nucleus. Dose-response studies indicated that sensitivity to morphine's rewarding property was increased by substantia nigra lesions and decreased by medial raphe lesions. Lesions of the dorsal raphe nucleus and of the locus coeruleus had no effect on self-administration behavior. An interaction between ascending dopaminergic and serotonergic pathways appears to be involved in the mechanism of morphine reinforcement.

Russell D. Cox

Papers

Nocturnal rotation in normal rats: Correlation with amphetamine-induced rotation and effects of nigro-striatal lesions

Differential effects of unilateral and bilateral caudate lesions on side preferences and timing behavior in rats.

Relationship of rats' spatial preferences effects of d-amphetamine on timing behavior

Changes in morphine self-administration after tel-diencephalic lesions in rats.

Changes in morphine self-administration after brainstem lesions in rats.