Search PubMed⌕ Search

Biomedical subjects

H J Markowitsch

Publications and source records attributed to H J Markowitsch.

143 records · Page 8Linked to original sources
PubMed1979

Cortical afferents to the prefrontal cortex of the cat: a study with the horseradish peroxidase technique.

Following horseradish peroxidase (HRP) injections into different areas within the prefrontal cortex (PFC) of the cat, labeled neurons were found in the cingulate and insular cortex. These results demonstrate that the cat's prefrontal cortex is reached directly from these cortical regions, and that the observed cortical projections are similar to those detected in the monkey's prefrontal cortex.

Animals↗
PubMed1978

Behavioral and anatomical consequences of small intrastriatal injections of kainic acid in the rat.

The effects of bilateral injections of kainic acid into the anteromedial neostriatal region were examined behaviorally and anatomically in two groups of rats. Behaviorally, kainic acid injections resulted in a severe impairment of delayed alternation retention, while the ability for visual discrimination remained unaffected. Anatomically it was found that axons traversing the injected area remain able to transport horseradish peroxidase. Furthermore, histological examinations of the injected regions revealed a heavy loss of neurons and a decrease of histochemical staining for specific acetylcholinesterase. Silver impregnation showed slightly disorganized, but continuous, axons in bundles of the capsula interna. On the other hand, the axonal network throughout the neuropil of the injected area was markedly diminished. No conspicuous change was found in myelin staining or in the intensity or catecholamine fluorescence. The anatomical results suggest that kainic acid appears to affect only perikarya of the neostriatum and the axons originating from these perikarya, whereas passing axons seem to remain intact. Thus, the observed behavioral impairment must be attributed to changes in the neostriatum itself. It is concluded that the neostriatum has 'complex' or 'cognitive' functions and that some mental symptoms in Huntington's chorea may be attributed to a dysfunction of this part of the brain.

Animals↗
PubMed1978

The prefrontal cortex of the cat: anatomical subdivisions based on retrograde labeling of cells in the mediodorsal thalamic nucleus.

Different areas of the frontal cortex of the cat were injected with small amounts of horseradish peroxidase. The region of labeled cells in the mediodorsal nucleus of the thalamus (MD) were related to the injected areas. Distinct relations between subdivisions of MD and of the prefrontal cortex were established: a rather large central sector of MD projects to the gyrus proreus and the anterior parts of the gyri sigmoideus, rectus, and frontalis. A narrow lateral band of anterior MD neurons projects predominantly to an area on both sides of the sulcus praesylvius, whereas a postero-lateral band sends fibers to a region on the ventral anterior sylvian gyrus. The area between the presylvian sulcus and the sylvian gyrus is apparently free of MD afferents, but not of other thalamic afferents. A fourth sector of MD, situated dorsomedially, projects to the middle parts of the gyri rectus and frontalis. And a fifth sector, located ventrally to the dorsomedial MD sector, projects to the ventral part of the gyrus rectus. The established subfields of MD and of the prefrontal cortex are discussed with respect to previous anatomical research in the cat.

Afferent Pathways↗
PubMed1978

Single unit activity in cat prefrontal and posterior association cortex during performance of spatial reversal tasks .

Relationships between the performance of complex learning tasks and the firing patterns of single unites in prefrontal and posterior association areas of the neocortex were studied in 9 cats. Recording data from 2 additional cats served as controls for sensory and motor aspects of the tasks employed. During recordings, animals sat in a box, their heads fixed to a stereotaxic instrument, and performed a non-sensory spatial reversal or delayed-alternation task by pressing 1 of 2 lateralized retractable levers. Units obtained were classified into 5 basic types according to their correlation with aspects of the tasks. The first 3 types were related directly to sensory, motor and motivational aspects of the tasks. The fourth type was named associative, as it contained units which changed firing rates in advance or as a consequence of environmental events, rather than in direct relation. Discharge changes of units of the fifth type were rated as non-specific or non-specifiable. Between recording areas and tasks a striking similarity of unit firing patterns was obtained. Differences were observed only between the reactivity of polymodal cells in prefrontal and in posterior fields, and in the proportions of units revealing mnemonic and motor response aspects. It was concluded that a considerable functional overlap between prefrontal and posterior association areas of the cat with respect to processing of complex learning tasks exists on the single neuron level.

Acoustic Stimulation↗
PubMed1977

A stereotaxic atlas of the prefrontal cortex of the cat.

A survey of existing atlases of the cat's brain has revealed a lack of coronal sections on the levels of the prefrontal cortex. On the other hand, neurophysiological and behavioral studies of this region have increased greatly in recent years. As the extent of coronal sections through the prefrontal cortex was seen to differ markedly even at separations of 1 mm, a stereotaxic atlas was made on the basis of brain sections of 16 mongrel cats. Brains were cut with the use of the paraffin or freezing method, and stained with cresyl violet, Luxol fast blue, or Kluver-Barrera's combination. Statistical methods were used to yield representative coronal outlines of sections from +20 to +30 mm anterior in 1 mm steps. A comparison with Reinoso-Suarez five coronal sections within this range showed a marked congruence between the two atlases.

Animals↗
PubMedDate not supplied

Kainic acid lesions in the cat's thalamus: morphological and behavioral changes.

Anatomical and behavioral effects of large and of circumscribed kainic acid lesions in the thalamus of the cat are described. Evidence is provided that even "athalamic" preparations seem possible and that cats with destruction of more than two thirds of their thalamus show only transitory disturbance of basic functions (eating, drinking, walking). It is concluded that fiber systems, traversing the thalamus, may be of particular importance for maintaining basic functions.

Animals↗
PubMedDate not supplied

Functional neuroimaging correlates of functional amnesia.

Especially in the field of memory encoding and retrieval, the results of functional neuroimaging have provided new insights in anatomico-functional interactions. In particular this holds true for the role of the prefrontal cortex in mnestic information processing, for the contribution and participation of the two hemispheres in various processes of information transmission, and for views on disturbed information processing after organically obvious and so-called psychogenic forms of memory impairments. This report particularly stresses the insights obtained by functional neuroimaging for probably environmentally triggered deficiencies in memory processing and discusses possible subtle neuroanatomical correlates of functional amnesias. It is especially emphasised that stress conditions and depressive states may modify the release of steroids (glucocorticoids) and transmitter agonists at the brain level with the consequence of selective memory disturbances which may manifest as a "mnestic block syndrome".

Amnesia↗
PubMedDate not supplied

Novelty and familiarity activations in PET studies of memory encoding and retrieval.

Nine young right-handed men viewed colored pictures of people, scenes, and landscapes. Then, 24 hr later while undergoing PET scanning, they viewed previously studied (OLD) pictures in one type of scan, and previously not seen (NEW) pictures in another. The OLD-NEW subtraction of PET images indicates familiarity, and the NEW-OLD indicates novelty. Familiarity activations, signalling aspects of retrieval, were observed in the left and right frontal areas, and posterior regions bilaterally. Novelty activations were in the right limbic regions, and bilaterally in temporal and parietal regions, including area 37. These latter activations were located similarly to novelty activations in previous PET studies using visual words and auditory sentences, suggesting the existence of brain regions specializing in transmodal novelty assessment. The effects of novelty are seen both behaviorally and in replicable patterns of cortical and subcortical activation. We propose a 'novelty/encoding hypothesis': (1) novelty assessment represents an early stage of long-term memory encoding; (2) elaborate, meaning-based encoding processes operate on the incoming information to the extent of its novelty, and therefore (3) the probability of long-term storage of information varies directly with the novelty of the information.

Brain↗
PubMedDate not supplied

The cognitive-mnestic performance profile of a patient with bilateral asymmetrical thalamic infarction.

The case of a 46-year old patient with a bilateral medial thalamic infarct, affecting mainly the region of the internal medullary lamina, but not of the mammillothalamic tract, is documented neuropsychologically and neuroradiologically. Testing was done after acute remission. The patient was of average intelligence but manifested a number of verbal memory problems. These are most likely attributable to the selective diencephalic damage and are interpreted as a disconnection syndrome.

Cerebral Infarction↗
PubMedDate not supplied

[Cognitive and mnemonic information processing in institutionalized and noninstitutionalized elderly patients].

Older subjects (institutionalized in a home for the aged and non-institutionalized) were compared in a test battery according to the recommendations of the NINCDS-ADRA. The institutionalized subjects were not distinguishable from the controls when only a small amount of information was to be processed or when the information had to be recalled with no distraction. Possible reasons for the observed differences are discussed.

Aged↗