Karl H. Pribram

Learning and limbic lesions

Abstract A model is presented which identifies the amygdala and hippocampus with two distinct attention-directing processes. The process to which the amygdala contributes is postulated to heighten awareness of experiences as a function of previous reinforcement, while the process to which the hippocampus contributes acts to diminish awareness of experience as a function of the probability of non-reinforcement. The manner in which these processes govern problem-solving behavior is outlined, and a number of hypotheses generated. These hypotheses were tested using monkeys with hippocampal and amygdaloid lesions. The results of these experiments were generally in agreement with the model, and the two lesion groups were found to be as distinct from each other as either group was from sham-operated controls.

The GSR of monkeys during orienting and habituation and after ablation of the amygdala, hippocampus and inferotemporal cortex ☆

Abstract In an effort to locate within the brain those systems essential for orienting and habituation, monkeys with lesions in the temporal lobe were tested for galvanic skin responses to a repeated pure tone stimulus and to a novel tone. Normal animals showed habituation of the GSR within 30 trials with distinctive reoccurrence of response to the novel tone. Animals with bilateral amygdalectomy had decreased GSR reactivity to both tones, whereas those with hippocampectomy and inferotemporal isocortex lesions had normal records. Consideration of this result in light of previous findings of a defect in behavioral habituation after amygdalectomy leads to the suggestion that the orienting reaction is involved not in the generation of reaction to novelty but, rather, in its registration in the central nervous system.

Effects of lesions of the medial forebrain on alternation behavior of rhesus monkeys.

Abstract In two experiments involving the delayed alternation task, monkeys with lesions of the hippocampal formation and monkeys with lesions of cingulate cortex were compared with controls. Either of these lesions caused impairment in original postoperative learning of delayed alternation; the hippocampal formation resections also produced a deficit in the retention of preoperatively acquired delayed alternation. The findings support the suggestion that these medial forebrain areas are related to cerebral systems which include the anterior frontal cortex, and that these areas are necessary to more than “emotional” behavior.

An experimental analysis of the behavioral disturbance produced by a left frontal arachnoidal endothelioma (meningioma)

Abstract A patient with a left frontal arachnoidal endothelioma was examined at the bedside. A series of simple tasks was administered. These showed: 1. (1) An inability to carry out compounded instructions whether these were given verbally or presented as a visual model. 2. (2) An inability to carry out “symbolic” instructions. 3. (3) These incapacities did not depend on any difficulty in apprehending the instructions per se . 4. (4) Error utilization appeared related to ease of disequilibration as tested by the orienting reaction. These results are believed to be indicative of frontal lobe impairment despite the presence of more generalized brain damage which may serve to bring out in relief and carricature the essence of a disturbance produced by the local lesion.

Social and emotional self-regulation.

In humans, frontal lesions result in deficits of social and emotional behavior that are often surprising in the presence of intact language and other cognitive skills. The connections between the motivation and memory functions of limbic cortex and the motor planning functions of frontal neocortex must be fundamental to meeting the daily challenges of self-regulation. The connectional architecture of limbic and neocortical networks suggests a model of function. The densely interconnected paralimbic cortices may serve to maintain a global motivational context within which specific actions are articulated and sequenced within frontal neocortical networks. The paralimbic networks represent the visceral and kinesthetic information that is integral to the representation of the bodily self. In a general sense, the implicit self-representation within paralimbic networks may shape the significance of perceptions and the motivational context for developing actions. The network architecture of the frontal lobe reflects the dual limbic origins of frontal cortex, in the dorsal archicortical and ventral paleocortical structures. In this paper, we speculated that these two limbic-cortical pathways apply different motivational biases to direct the frontal lobe representation of working memory. The dorsal limbic mechanisms projecting through the cingulate gyrus may be influenced by hedonic evaluations, social attachments, and they may initiate a mode of motor control that is holistic and impulsive. In contrast, the ventral limbic pathway from the amygdala to orbital frontal cortex may implement a tight, restricted mode of motor control that reflects adaptive constraints of self-preservation. In the human brain, hemispheric specialization appears to have led to asymmetric elaborations of the dorsal and ventral pathways. Understanding the inherent asymmetries of corticolimbic architecture may be important in interpreting the increasing evidence that the left and right frontal lobes contribute differently to normal and pathological forms of self-regulation.

Hypnotic Hallucination Alters Evoked Potentials

Brain electrical potentials evoked by visual stimulation were analyzed to study the neurophysiological mechanism associated with hypnotic hallucination. The visual evoked responses of 6 highand 6 low-hypnotizable subjects were compared in three hypnotic conditions: stimulus enhancement. stimulus diminution, and stimulus elimination (obstructive hallucination). High-hypnotizable individuals demonstrated significant suppression of the later components of the evoked response (N2 and Pl ) while experiencing obstructive hallucinations, indicating a change in information processing. This effect was significantly greater in the right. as compared to the left, occipital region.

Psychophysiological indices of cerebral maturation

Maturation (1-21 yr) trajectories for quantitative electroencephalographic (QEEG) frequency spectra are presented for four regions of the human brain. The results show that all four regions exhibited discontinuous maturation rates: five stages were identified. The stages were synchronous across regions during the first 10 1/2 years of life. Thereafter, the four maturation trajectories became independent of one another. Interestingly, a major maturational advance was recorded from the frontal regions, during late adolescence. The relationships between these findings to maturation rates in skull volume, cortical thickness, cortical volume and nerve cell density measurements was discussed. These converging results indicate that the observed QEEG stages can reliably be interpreted as landmarks in cerebral maturation.

While a Monkey Waits: Electrocortical Events Recorded During the Foreperiod of a Reaction Time Study

Abstract Electrical potentials in frontal, motor and parietal cortex of young rhesus monkeys during three foreperiod reaction time tasks were studied using transcortical Pt-PtCl electrodes, long time-constant amplifiers and computer-averaging techniques. A prominent positive-negative-positive wave form was observed maximally in postcentral cortex when monkeys held a key down during a fixed interval between two stimuli. When response was withheld until the second stimulus, sustained negativity occurred frontally but not postcentrally. The relationship of contingent negative variation, motor potentials and the observed electrocortical patterns is discussed.

EEG correlates of hypnotic susceptibility and hypnotic trance: spectral analysis and coherence

EEG was recorded monopolarly at frontal (F3, F4), central (C3, C4) and occipital (O1, O2) derivations during A-B-A conditions of waking rest, hypnosis (rest, arm immobilization, mosquito hallucination, hypnotic dream), and waking rest. Stringently screened on several measures of hypnotic susceptibility, 12 very low hypnotizable and 12 very highly hypnotizable, right-handed undergraduate, subjects participated in one session. Evaluations were Fast-Fourier spectral analysis, EEG coherence between selected derivations and maximum spectral power within EEG bands. In eyes open and closed conditions in waking and hypnosis, highly hypnotizable subjects generated substantially more mean theta power than did low hypnotizable subjects at all occipital, central and frontal locations in almost all conditions of waking and hypnosis, with a larger difference in frontal locations. Both low and high hypnotizables showed increased mean theta power in hypnosis, suggesting an intensification of attentional processes and imagery enhancement. Mean alpha power was never a predictor of hypnotic susceptibility. Interactions with hypnotic susceptibility showed that highly susceptible subjects had more beta activity in the left than right hemispheres, while low susceptible subjects showed only weak asymmetry. No main effects for or interactions between waking/hypnosis and hypnotic level were found for coherence between derivations or maximum spectral power within theta, alpha and beta EEG bands.

THE PRIMATE FRONTAL CORTEX - EXECUTIVE OF THE BRAIN

Publisher Summary The primate frontal lobe can be divided into three major parts: (1) the medial, defined by its projections from the anterior nuclear group; (2) the dorsolateral, defined by its projections from the microcellular portion of the medial thalamic nucleus; and (3) the posterior orbital, deriving projections from the midline of the thalamus and so heavily connected to the adjacent anterior insula, temporal pole, and periamygdaloid cortex. This chapter illustrates a model of inhibitory interactions that took place within the afferent channels. Collateral and recurrent afferent inhibitions were bucked against one another, forming a primary couplet of neural inhibition within afferent channels. Four forebrain mechanisms were assumed to provide efferent control on the primary couplet. Two of those—frontotemporal and sensory specific-intrinsic—influenced the couplet by regulating collateral inhibition whereas two others—hippocampal and polysensory motor—regulated recurrent inhibition. The frontal cortex appeared critically involved in implementing executive programs when those were necessary to maintain brain organization in the face of insufficient redundancy in input processing and in the outcomes of behavior.