Jan C. Jackson

Arousal Systems and Infant Heart Rate Responses

Publisher Summary Several writers have recently proposed that there are two arousal systems that affect behavior differently; one energizing response while inhibiting receptive and consolidative processes and the other facilitating these processes and, thus, memory and learning. Sokolovs work, in particular, has stimulated considerable interest but attention has been largely focused on the facilitative “orienting” system to the neglect of an opposite-acting “defense” system. This chapter considers the evidence from adult studies that these two systems can be distinguished by the direction of heart rate (HR) change. It reviews typical procedures and problems encountered in studies of infant HR response and review the data from these studies to determine whether there is a developmental shift from primarily defensive reactions during the newborn period to increasingly probable and larger orienting reactions with increasing age.

Cortical projections of the thalamic mediodorsal nucleus in the rabbit.

The cortical projection of the thalamic mediodorsal nuclear complex (MD) in the rabbit was mapped retrograde horseradish peroxidase and anterograde tritiated proline techniques. The projection field occupied the entire medial wall rostral to a mid corpus callosal level, wrapped around the frontal pole onto the lateral convexity and tailed off caudally on the dorsal bank of the rhinal sulcus. The projection of the lateral approximately one-half of MD, the half which does not receive olfactory input, was confined to medial cortex supply all but the most rostral region. This projection field of lateral MD was precisely organized in two dimensions with the most lateral part projecting most caudally and the most dorsal part projecting most ventrally. A representation for the third, anterior-posterior (A-P), dimension was not evident since any cortical point within the field was supplied by a cylinder of cells extending the entire A-P extent of lateral MD. The medial half of MD, which does receive olfactory input, projected to the remaining rostral medical cortex, the lateral convexity and rhinal sulcal region. The inverse dorsoventral relationship was partially preserved and on overlapping A-P gradient was present with sulcal projections originating more caudally in medial MD and the rostral medial projection originating more rostrally.

Unit discharges in the mediodorsal nucleus of the squirrel monkey evoked by electrical stimulation of the olfactory bulb

Summary The thalamic mediodorsal nucleus (MD) of the squirrel monkey was explored with microelectrodes for units responsive to electrical stimulation of the olfactory bulb. All responsive units were localized throughout the magnocellular subdivision of MD, most (88%) ipsilateral to the stimulated bulb. Other parts of MD were unresponsive. Latencies to the first poststimulus spike ranged from 4 to 50 msec with a median value of 14 msec. In preparations with both frontal poles ablated eliminating the possibility of stimulus spread to orbitofrontal cortical neurons and subsequent anti- or orthodromic activation of Mc cells, the shortest response latency was 6 msec. Thus relatively direct and extensive connections exist between the olfactory bulb and one cytoarchitectonic subdivision of this prominent ‘association’ nucleus in a microsmatic primate.

Cardiac orienting responses as a function of age

He art-rate changes, recorded from human Ss under conditions appropriate for eliciting orienting, were curvilinearly related to age and independent of differences in prestimulus heart rate. Deceleration was absent at birth, increased from 6 to 16 weeks, and lessened between 16 weeks and young adulthood.

Unit discharges in the mediodorsal nucleus of the rabbit evoked by electrical stimulation of the olfactory bulb

Summary The mediodorsal nucleus of the thalamus (MD) in rabbits was explored with microelectrodes during electrical stimulation of the olfactory bulb and tract. In agreement with previous results in the squirrel monkey, unit responses were located within the medial half of MD. Response patterns included early discharges with latencies of 50 msec or less, late discharges with latencies of more than 100 msec, or dual early and late responses. The interval between early and late responses was characteristically a silent period even in units with spontaneous activity. Units which responded at an early latency were more commonly seen than those which showed only a late response. Latencies to first spike within the former group ranged from 15 to 50 msec (median = 36 msec) when the rostral olfactory bulb was stimulated and from 8 to 36 msec (median = 20m sec) when the stimulating electrode was in the rostral retrobulbar area adjacent to the lateral olfactory tract. Major features of response showed some parallels with results obtained both in the squirrel monkey MD and in the cat prepyriform cortex, a structure reported to have direct anatomical connections with the medial portion of MD.

An autoradiographic study of subcortical forebrain projections from mediodorsal and adjacent midline thalamic nuclei in the rabbit

Abstract Conclusions from lesion studies on the subcortical efferent connections of the thalamic mediodorsal nucleus have been varied and conflicting. In this autoradiographic study, tritiated proline was injected into the mediodorsal nucleus and adjacent midline nuclear areas (intermediodorsal nucleus and paraventricular nucleus of the thalamus) of 18 rabbits. Terminal labeling from injections that included parts of the paraventricular nucleus was seen in the following ipsilateral areas: central amygdaloid nucleus, lateral septum, a restricted portion of the nucleus of the stria terminalis, entorhinal cortex and the entire extent of the medial (periventricular) hypothalamus. Injections that encroached into the intermediodorsal nucleus produced ipsilateral labeling in most of the nucleus accumbens, layers II and III of the olfactory tubercle, the magnocellular portion of the posterolateral basal amygdaloid nucleus and the caudate nucleus. Injections restricted to the mediodorsal nucleus produced labeling only in the ipsilateral caudate nucleus. It is concluded that medial portions of the mediodorsal nucleus only project to the caudate nucleus; whereas the midline nuclei project to the other eight subcortical areas in addition to the caudate nucleus. By attributing to the midline nuclei many of the projections previously associated with the mediodorsal nucleus, many discrepancies from earlier reports can be explained by lesion of fibers of passage. Efferent functional relationships of the mediodorsal nucleus with subcortical centers may be established through the caudate projections or projections to other thalamic structures, such as the adjacent midline nuclei.

The distribution of olfactory input in the opossum mediodorsal nucleus.

Discharges of single cells in the thalamic mediodorsal nucleus (MD) of the opossum were recorded during electrical stimulation of the lateral olfactory tract. Responsive sites were histologically localized throughout the entire mediolateral extent of MD. In both rabbit and squirrel monkey responses are confined to the medial half of MD. Thus the lateral non-olfactory nuclear subdivision, common to both rabbit and squirrel monkey, was not found in the opossum. Firing patterns of cells were similar to those observed in rabbit and squirrel monkey. They commonly consisted of an early spike or burst of spikes, followed by a period of inactivity and then, in many cells, by a later period of response or of resumed spontaneous activity. The results indicate that olfactory input is characteristic of MD in a diverse sample of mammals but that topographic organization of the input is distinctly different in the opossum.