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O D Creutzfeldt

Publications and source records attributed to O D Creutzfeldt.

At least 19 recordsLinked to original sources
PubMed1994

Receptive field analysis and orientation selectivity of postsynaptic potentials of simple cells in cat visual cortex.

Postsynaptic potentials (PSPs) were recorded from cat striate cortical cells by the whole-cell in vivo recording technique using patch-clamp electrodes. EPSPs and IPSPs evoked by flashing bars on the receptive field at different positions and orientations revealed the spatial structure of the excitatory and inhibitory inputs. The elongation of the excitatory input field (length:width ratio) was found to be minimal (mean ratio of 1.7) and much lower than those reported for spike discharges. Two-dimensional receptive field response profiles of early PSPs were recorded by flashing a small spot of light over a square matrix covering the receptive field. These recordings also showed only mild degrees of elongations of the receptive field. Such elongations could be the result of either an excitatory input from the geniculate that is already biased for orientation or an excitatory convergence from a limited number of LGN fields arranged in a row. In most first-order cells, we found that inhibition was contributing significantly to orientation selectivity. Often prominent IPSPs could be evoked by stimuli of nonoptimum orientations. Presence of inhibition could also be inferred by the way that EPSPs were sharply cut off by inhibition. When the amplitude of an EPSP was measured at different latencies after its onset, the EPSP was found to be very broadly tuned to orientation at the beginning, but showing increasing orientation selectivity with time. It is proposed that this progressive development of orientation selectivity is due to (1) inhibitory inputs arriving after the first wave of excitation, (2) intracortical excitatory inputs from other cells tuned to similar orientations, and (3) voltage-sensitive mechanisms such as NMDA channels.

Animals↗
PubMed1993

Functional comparison of neuronal properties in the primate posterior hippocampus and parahippocampus (area TF/TH) during different behavioural paradigms involving memory and selective attention.

Monkeys were trained on a delayed match-to-sample (DMS) task. In addition a standardized behavioural trial was performed which involved an experimenter approaching the animal in certain sequence and presenting edible or other objects ('raisin trial'). Neuronal activity of 617 units was recorded in the posterior parahippocampus (PH) and in the posterior hippocampus (H). In many cases, we compared the activity of the same neuron in different tasks. 32.7% of the 455 PH neurons and 28.5% of the 130 H cells responded during the presentation of the visual stimuli in the DMS task. These responses were only mildly influenced by the physical dimensions of the visual stimulus, but often depended on the context in which the stimuli were presented. There was no differential response to the second stimulus that clearly depended on the nature of the first stimulus. 6.2% of the PH units, but none in H, responded in relation to the reward. 4.4% of the PH neurons, but none in H, showed a mild response during the interstimulus interval. 38.1% of 215 PH neurons and 37.8% of 45 H cells responded during one or more phases of the raisin trial. These responses were not related to the physical dimensions of the sensory stimuli. 210 PH and 41 H units were investigated during the DMS task as well as during the raisin trial. 18.1% (PH) and 12.2% (H) of the units responded during the DMS task, but not during the raisin trial; 17.1% (PH) and 36.6% (H) responded vice versa. A response in both trials was found in 17.1% of the PH neurons, but in none of the H cells. There were also other PH unit types showing responses during different aspects of the DMS task and even in other control paradigms, while no such overlap was encountered in H. Our results suggest a function of H and PH in the evaluation of the behavioural significance of sensory information. It may be this aspect which leads to anterograde memory disturbances after lesion of these areas. Since representation of neuronal information was found to be more specific in H, a possible function as an 'evaluation index' is discussed.

Acoustic Stimulation↗
PubMed1993

The neurophysiological correlates of colour induction, colour and brightness contrast.

Psychophysical experiments suggest that colour contrast and colour induction by surround lights can be explained as brightness contrasts (darkness induction) in the spectral region of the surround colour. It follows from this model that a chromatic surround reduces the gain of receptor-ganglion cell channels if the surround colour is in their excitatory spectral region. Thus, a green-sensitive cell (G+/R- or WS in our nomenclature) would respond less to a blue-green stimulus flashed into its receptive field when the surround (5 degrees/20 degrees inner/outer diameter) is illuminated with blue light. Neurophysiological experiments show that this is indeed the case and that such surround-induced response changes are present already in relay cells of the parvocellular layers of the lateral geniculate nucleus (P-LGN) and their retinal afferents. These surround-induced response changes are in qualitative and quantitative agreement with psychophysical experiments. Since the neuronal signal for white consists of a balanced excitation of the M-cone excited, green-blue-sensitive WS-cells and the L-cone excited, yellow-red-sensitive WL-cells, the findings also explain colour induction on white surfaces as well as coloured shadows: during blue surround illumination, white signals from the WS-cells, and during red surround the white signals from the WL-cells are reduced. The neurophysiological surround effects on P-LGN cells are identical but weaker than those produced by light of the same colour shone into the receptive field centres. They are therefore undistinguishable from direct adaptation of those receptors which feed directly into the receptive field of the respective cells. This suggests that they are caused by scattered light reaching the receptive field from the surround.

Animals↗
PubMed1992

Postsynaptic potentials in cat visual cortex: dependence on polarization.

During the investigation of visually evoked postsynaptic potentials (PSPs) of visual cortical neurons, we recorded cell activity under different levels of membrane potential. In some cases, however, dependence of these PSPs on the level of membrane polarization appears to be inconsistent with the conventional scheme. One disagreement was the reduction, instead of an increase, of excitatory potentials during hyperpolarization of the cell. The other point was that depolarization of the cell often leads to increase of the amplitude of both excitatory and inhibitory postsynaptic potentials. This inconsistency may suggest the involvement of voltage-dependent ion channels in generating PSPs to visual stimuli. A possible way of separating the excitatory and inhibitory components of the response by polarization of the cell in spite of the presence of voltage-dependent channels and possible implications of this mechanism in the visual cortex are discussed.

Animals↗
PubMed1991

Unit activity in the hippocampus and the parahippocampal temporobasal association cortex related to memory and complex behaviour in the awake monkey.

Monkeys (Macaca fascicularis) were trained on a delayed match-to-sample (DMS) task using delays of upto 20 s. Unit activity was recorded from the hippocampus and the temporo-basal association cortex in the lateral parahippocampal region (partly corresponding to TF and TH) during the DMS task, as well as during a visual object discrimination task and some behavioural situations involving the experimenter. Units were encountered that gave visual responses which were sometimes context-dependent. Changes in discharge rate during the delay period of the DMS task were very rare and when present, very weak. On the other hand, many neurones, including some of those which were unresponsive during the DMS task fired vigorously (or were inhibited) during situations which involved attention, expectation or food consumption. For example, the neurones' firing rate was altered when the cage door was opened or closed, the experimenter entered or left the room or showed the monkey a piece of food before giving it to him. A variety of such responses in complex behavioural situations were seen, sometimes even in neurones which did not respond in the DMS task. Activity changes in neurons of the temporo-basal cortex thus appear to be related to the internal state associated with a stimulus and even some of the responses obtained in the DMS task can be interpreted as being related to changes in the behavioural state rather than to the mnemonic elements of the task.

Action Potentials↗
PubMed1991

The neurophysiological correlates of colour and brightness contrast in lateral geniculate neurons. I. Population analysis.

The colour of an object is changed by surround colours so that the perceived colour is shifted in a direction complementary to the surround colour. To investigate the physiological mechanism underlying this phenomenon, we recorded from 260 neurons in the parvo-cellular lateral geniculate nucleus (P-LGN) of anaesthetized monkeys (Macaca fascicularis), and measured their responses to 1.0-2.0 degrees diameter spots of equiluminant light of various spectral composition, centered over their receptive field (spectral response function, SRF). Five classes of colour opponent neurons and two groups of light inhibited cells were distinguished following the classification proposed by Creutzfeldt et al. (1979). In each cell we repeated the SRF measurement while an outer surround (inner diameter 5 degrees, outer diameter 20 degrees) was continuously illuminated with blue (452 nm) or red (664 nm) light of the same luminance as the center spots. The 1.0-1.5 degree gap between the center and the surround was illuminated with a dim white background light (0.5-1cd/m2). During blue surround illumination, neurons with an excitatory input from S- or M-cones (narrow- and wide-band/short-wavelength sensitive cells, NS- and WS-cells, respectively) showed a strong attenuation of responses to blue and green center spots, while their maintained discharge rate (MDR) increased. During red surround illumination the on-minus-off-responses of NS- and WS-cells showed a clear increment. L-cone excited WL-cells (wide-band/long-wavelength sensitive) showed a decrement of on-responses to red, yellow and green center spots during red surround illumination and, in the majority, also an increment of MDR. The response attenuation of narrow-band/long-wave-length sensitive (NL)-cells was more variable, but their on-minus-off-responses were also clearly reduced in the average during red surrounds. Blue surround illumination affected WL-cell responses little and less consistently than those of NL-cells, but often broadened the SRF also in the WL-cells towards shorter wavelengths. The M-cone excited and S-cone suppressed WM-cells were strongly suppressed by blue but only little affected by red surround illumination. The changes of spectral responsiveness came out clearly in the group averages of the different cell classes, but showed some variation between individual cells in each group. The zero-crossing wavelengths derived from on-minus-off-responses were also characteristically shifted towards wavelengths complementary to those of the surround.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1991

The neurophysiological correlates of colour and brightness contrast in lateral geniculate neurons. II. Adaptation and surround effects.

We report on experiments which were undertaken in an attempt to clarify mechanisms underlying the contrast effects of chromatic surround illumination on spectral responsiveness of cells in the parvocellular layers of the LGN (P-LGN-cells), that had been demonstrated under standard conditions in the preceding companion paper. The experiments were done in anesthetized macaques (Macaca fascicularis). In some neurons, S-potentials were recorded together with the post-synaptic action potentials, and all effects seen in P-LGN-cells were present already in their retinal afferents indicating their retinal origin. The responsiveness of the cells for center stimuli of different wavelengths and during illumination of the receptive field center or the outer surround was determined. Continuous outer surround illumination altered maintained discharge rate (MDR), sensitivity and gain of P-LGN and retinal ganglion cells in the same way and empirically not distinguishable from direct illumination of the receptive field. Responses to surround flashes showed the same dependence on spectral composition as those to center flashes. Adaptation and excitation caused by outer surround illumination (inner diameter 5 degrees, outer diameter 20 degrees) were, in the average, ten times weaker than those exerted by light of the same spectral composition shone directly into the receptive field. Surround effects decreased proportional to r-2. Excitation by outer surround flashes was reduced by adaptation of the receptive field center in the same manner as responses to center flashes. The findings indicate that outer surround light has a direct excitatory and adaptive effect on the excitatory or inhibitory cones feeding into the receptive field. This indicates that straylight from the surround into the center could be responsible for the adaptive and excitatory effects of surround illumination. The straylight fraction from the remote surround into the receptive field must be higher, however, than that estimated from the psychophysically determined point spread function. It comes closer to earlier direct straylight measurements in excised eyes, but may be enhanced by chromatic aberration. If a surround of excitatory colour is flashed simultaneously with an excitatory center stimulus, additivity of center and surround excitation is observed only at low center intensities, while at higher center intensities the gain for center excitation is reduced similar to adaptive gain control. This could be explained by lateral interaction through horizontal connections in the retina, which decays within seconds, while adaptation of the cones feeding into the receptive field center is fully effective only after about 3 s.(ABSTRACT TRUNCATED AT 400 WORDS)

Adaptation, Ocular↗
PubMed1991

Regional and temporal expression of sodium channel messenger RNAs in the rat brain during development.

The distribution of mRNA expression for three types of voltage gated neuronal sodium-channels was studied in the rat brain at different developmental stages (embryonal day E18, postnatal day P5 and adult). With the in-situ hybridization technique, using synthetic DNA-oligomer probes, pronounced regional and temporal variations in the expression levels of the different channel subtypes could be detected. In comparison with types I and III, sodium channel II mRNA was the most abundant subtype at all developmental stages. Maximal expression of sodium channel II mRNA was seen at P5 in virtually all parts of the grey matter, except for the cerebellum. In adult rat brain in contrast, sodium channel II mRNA levels were maximal in the granular layer of the cerebellum, whereas in all other regions expression had decreased to roughly 50% of postnatal levels. Na channel I expression was virtually absent at E18 and showed highest levels at P5, with maxima in the caudate nucleus and hippocampus. In the adult brain, expression of Na-channel I was nearly absent in the neocortex, but well detectable in the cerebellum and, at lower levels in the striatum and thalamus. Sodium channel III was mainly expressed at the embryonal stage and showed a decrease to very low levels with little regional preferences in the adult.

Animals↗
PubMed1991

Topographical and topological organization of the thalamocortical projection to the striate and prestriate cortex in the marmoset (Callithrix jacchus).

In eleven hemispheres of nine marmoset monkeys (Callithrix jacchus), we have investigated the thalamo-cortical organization of the projections from the pulvinar to the striate and prestriate cortex. In each experiment, single or multiple injections of various retrograde fluorescent tracers were injected into adjacent regions or areas. In two experiments, horseradish peroxidase (HRP) was injected into the lateral geniculate nucleus (LGN) and the lateral pulvinar, respectively. The results show that the thalamo-cortical projection from LGN to striate cortex and from pulvinar to the prestriate cortex are similarly organized, but the geniculo-striate projection is more precise than the pulvinar-prestriate projection. The pulvinar-prestriate projection is topographically organized and preserves topological neighbourhood relations. Projection zones to the various visual areas are concentrically wrapped around each other. The projection zone to area 18 constitutes a central core region. It begins ventro-laterally in PuL where the pulvinar is in contact with the LGN. This contact zone we called the hilus region of the pulvinar. The area 18-projection zone stretches as a central cone into the posterior pulvinar through PuL and into PuM. It is surrounded by the projection zone to the posterior belt of area 19 and this in turn is surrounded by the projection zone to the anterior belt of area 19. The projection zones to area 19 are then surrounded medially and dorsally by zones projection to the temporal and parietal association cortex, respectively. The projection zone to area MT is located medio-ventrally in the posterior pulvinar (PuIP and surrounding nuclei) and coincides with a densely myelinated region. Area 17 also receives input from the pulvinar but probably predominantly in the region of the central visual field. The pulvinar zone projecting to area 17 is located ventrolaterally from the central core region projecting to area 18 and is contiguous laterally with the LGN. If the positions of the vertical and the horizontal meridian in the pulvinar correspond to those in the respective cortical projection zones, a second order visual field representation such as found in area 18, with the horizontal meridian split at an eccentricity of about 7-10 degrees, can also be recognized in the pulvinar.

Acetylcholinesterase↗
PubMed1991

The local domain for divergence of subcortical afferents to the striate and extrastriate visual cortex in the common marmoset (Callithrix jacchus): a multiple labelling study.

In the common marmoset (Callithrix jacchus), the cortical projection from the pulvinar and other diencephalic structures into the striate and prestriate cortex was investigated with various fluorescent retrograde tracers. Single cortical injections as well as multiple injections at distances of 1-2 mm with one tracer into an extended but coherent cortical region were applied. Fields with multiple injections were placed so that they touched each other (minimal distances 2 to 3 mm). Retrogradely labelled cells in the LGN and/or the pulvinar were arranged in coherent columns, volumes or slabs, but cell volumes resulting from neighbouring cortical injections overlapped at their border (for details of the thalamo-cortical topography see the companion paper Dick et al. (1991]. Double labelled cells (dl) were only found in the zones of overlap of the cell volumes labelled by the respective tracers. The relative number of dl-cells in these overlap zones was 6.2 +/- 3.1%. The dl-frequency was the same in the various nuclei of the pulvinar and the LGN. In the main layers of LGN, dl-cells were found only in the overlap zone of two injection fields into area 17, but a few dl-cells were found in interlaminar cells after injections into area 17 and 18. Maximal cortical distances between injection fields which produced dl in the pulvinar, were 3 to exceptionally 4 mm but dl was highest at injection distances less than or equal to 2.5 mm and decreased sharply at wider distances. Such overlap zones were concerned with identical or overlapping regions of visual field representation in the cortex and probably also in the pulvinar. Although in individual experiments up to four different tracers were injected into different striate/prestriate regions, often embracing the same visual field representation, individual cells in the pulvinar showed dl from maximally only two tracers injected into neighbouring cortical regions. We conclude that dl in the posterior thalamic projection nuclei is determined essentially by cortical distance and thus reflects the local domain of branching of thalamo-cortical afferents. Pruning of such branches during development may further restrict bifurcating axons to identical visual field representations, but representation of identical visual field regions in different visual areas is not, per se, a sufficient condition for dl. It is not found if such regions are further apart from each other than the typical local domain of 2-3 mm, exceptionally up to 4 mm in one experiment after injections into area 17 and MT.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1991

Topographical mapping of the thalamocortical projections in rodents and comparison with that in primates.

The general topographical organization of the thalamo-cortical projection of two rodents, the Siberian hamster (Phodopus sungorus) and the Guinea pig (Cavia aperta) was investigated with the HRP-method and compared with that of the new world primate marmoset (Cal-lithrix jacchus) as shown in a companion study by Brysch et al. (1990). HRP was injected into various regions of the cortex in different animals and hemispheres, and plots were made of the retrogradely stained thalamic projection neurons. The thalamocortical projection is virtually identical in both rodent species. It is topological throughout in that nearby cortical injections label nearby, though overlapping cell groups in the thalamus. Cortical injections in a rostro-caudal progression labelled thalamic projection zones on top of each other, layered like tiles on a roof or fish scales, beginning in the rostromedial and ending in the caudo-dorsal thalamus. The progression vector of thalamic zones projecting successively from more rostral to more caudal cortical zones is twisted and turns from a predominantly mediolateral direction in the anterior thalamus to an essentially ventro-dorsal direction in the posterior thalamus In the marmoset, the thalamo-cortical topography follows the same topological rule, with the exception of the lateral geniculate body which is translocated latero-ventrally and separated from the rest of the thalamus as in all primates. This suggests a general thalamo-cortical mapping rule common to all mammals which can be related to gradients and timing of cell birth in the thalamus. It is proposed that this mapping rule is the consequence of successive appositions of neurons in the medio-ventral thalamus during ontogenetic development.

Animals↗
PubMed1991

Whole cell recording and conductance measurements in cat visual cortex in-vivo.

Long and stable recordings of post-synaptic, action and membrane potentials from visual cortical neurons in-vivo, are possible with the patch-clamp technique. These are comparable to the whole-cell configuration, but with an incomplete seal. EPSPs and IPSPs of normal time course and up to several mV can be recorded. DC potentials ranged from - 30 to - 60 mV and input resistances from 50 to 150 M omega. Injected currents have the same effect as if applied intracellularly. Membrane conductance after electrical stimulation of the lateral geniculate nucleus is increased during the first 20 ms, but decreases from 60 to about 130 ms, during return of the membrane potential to its resting level. The recording method is compared to other intracellular recording techniques in-vivo and in-vitro.

Animals↗
PubMed1990

Afferent connections of the prelunate visual association cortex (areas V4 and DP).

The afferent and efferent connections of the prelunate visual association area V4 of macaque monkeys were investigated by means of the horseradish peroxidase (HRP) method. The specific thalamic afferents from the dorsolateral segment of the medial pulvinar and the lateral segment of the inferior pulvinar were topographically organized. A band of cells was labelled in the intralaminar nuclei (nucl. centr. med. and lat., reaching into LD and the most dorsal part of VL), and a few cells in the interlaminar layers of the lateral geniculate body. Other diencephalic afferents included the claustrum, the nucleus basalis Meynert and the pars compacta of the substantia nigra. Ipsilateral cortical areas which projected into V4 included area 18 (V2), the inferior parietal cortex, the anterior and posterior parts of the superior temporal sulcus, the frontal eye fields and the temporo-basal association cortex on the lateral half of the parahippocampal gyrus and around the occipito-temporal sulcus. In the contralateral cortex, discontinuous regions in areas V4 and V5 on the prelunate gyrus and some cells at the 17/18-border were labelled. All regions in which labelled cells were found and, in addition a restricted region in the dorsal cap of the head and the tail of the caudate nucleus showed fibre and terminal labelling. In addition mesencephalic afferents and efferents were identified but not investigated in detail. An attempt to estimate the quantitative contribution of the various afferent systems to the prelunate cortex was made by counting the labelled cells in the different areas. The afferent and efferent organization of the prelunate visual association area indicates that it is incorporated in a network of cortical and subcortical regions involved in various aspects of visual behavior.

Afferent Pathways↗
PubMed1990

The topology of the thalamo-cortical projections in the marmoset monkey (Callithrix jacchus).

This paper addresses the question of a general topological principle of thalamo-cortical projections. In the lissencephalic primate brain of the common marmoset (Callithrix jacchus), large injections of horseradish peroxidase were made in various parts of the neocortex. These injections were placed in different animals and hemispheres along various caudo-rostral and medio-lateral gradients. Labelled cells in the thalamus were plotted and the labelling-zones resulting from several injections along a medio-lateral and two caudo-rostral cortical vectors were drawn into semi-schematic thalamic maps. These composite maps reveal a topological organization of the whole thalamo-cortical projection. The thalamic representation of the caudo-rostral and medio-lateral gradients indicate a rotation of the posterior relative to the anterior thalamus. An attempt is made to relate the organization of the thalamo-cortical projection to the development of the thalamus and the cortex. The cortex is divided into concentric zones around the sensory-motor and insular cortex. The thalamus is divided into corresponding projection zones. The topology of thalamo-cortical connections can then be regarded as a consequence of corresponding thalamic and cortical growth gradients. This is not only consistent with the general thalamo-cortical topology and the inversion of maps from thalamus to cortex, but also explains the continuity and overlap of thalamic projection zones in the pulvinar to widely separated cortical areas as the parietal, temporal and frontal association cortex.

Animals↗
PubMed1989

Attention and eye movement related activation of neurons in the dorsal prelunate gyrus (area DP).

Neurons in area DP, the dorsomedial portion of the prelunate gyrus of awake monkeys (Macaca mulatta and Macaca sylvana), responded only little if at all to stationary or moving light stimuli. Circumscribed receptive fields could not be determined in the majority of cells. About 25% of the units became active at a certain gaze position, mostly ipsilateral to the recording site, and with a latency of 70-150 ms after the eye had attained this position with a saccade. About 70% of neurons were activated vigorously when the monkey looked attentively at an object, such as a face, a glove, a hand or simply towards the opening door, and explored it visually. These stimuli elicit attention as well as emotional responses. Photographed objects or faces flashed on a screen produced only little if any response. Our observations, therefore, suggest that the dorsomedial part of the prelunate gyrus may represent activities related to behavioral aspects of vision rather than to features of the visual image itself.

Animals↗
PubMed1989

Functional subdivisions in the auditory cortex of the guinea pig.

The auditory fields in the cortex of the guinea pig were investigated with microelectrode mapping techniques. Pure tones of varying frequencies and amplitudes were used as acoustic stimuli. Mainly, multiunit activity was recorded. A large tonotopic area is found in the anterior half of the auditory cortex. This area is named the anterior field (field A). Frequency tuning curves of multiunits in field A are generally narrow. Responses to tone stimuli are strong, and latencies are short. Low best frequencies are represented rostrally, high best frequencies caudally. The tonotopy is continuous and quite regular. Field A is narrow dorsally and becomes gradually broader ventrally. Correspondingly, the isofrequency lines slightly diverge from dorsal to ventral. Caudal to the first field, there is a second, smaller tonotopic area. It lies in the dorsal half of the posterior auditory cortex and is therefore named the dorsocaudal field (field DC). The frequency specificity of the cell clusters in this area is as strong as in field A, but the tonotopy is discontinuous: In the dorsal half of field DC, high best frequencies (16-32 kHz) are represented rostrally; the low frequencies (0.5-2.8 kHz) are represented immediately caudal to the high frequencies, while the intermediate frequencies are missing. Ventrally in field DC, the frequency representation is more complete. Except for this discontinuous map, we did not notice any differences between fields A and DC. A third tonotopic field was found rostral to field A. This field extends over a surface of less than 1 mm2 and was named the small field (field S). It contains a complete representation of the frequency range; high best frequencies are located rostrally, low frequencies caudally. The response latencies are slightly longer in field S than in fields A or DC, and the tuning curves are broader. A broad strip of nontonotopic cortex (auditory belt) surrounds fields A and DC caudally. We subdivided this area into the dorsocaudal and the ventrocaudal belt region. In both areas, tuning curves are often broad, and response latencies are longer than in the tonotopic cortex. In the dorsocaudal belt, most multiunits react with a phasic on-response to pure tones; in the ventrocaudal belt, tonic responses occur more frequently. Another nontonotopic region is located in the anterior auditory cortex, rostral to the tonotopic fields, and was therefore named the rostral belt. Tuning curves in this area are broad, latencies are short, and response thresholds are often high. In the discussion, the guinea pig is compared with other mammalian species.(ABSTRACT TRUNCATED AT 400 WORDS)

Acoustic Stimulation↗
PubMed1989

Anatomy of the auditory thalamocortical system of the guinea pig.

We investigated the projection from the medial geniculate body (MG) to the tonotopic fields (the anterior field A, the dorsocaudal field DC, the small field S) and to the nontonotopic ventrocaudal belt in the auditory cortex of the guinea pig. The auditory fields were first delimited in electrophysiological experiments with microelectrode mapping techniques. Then, small quantities of horseradish peroxidase (HRP) and/or fluorescent retrograde tracers were injected into the sites of interest, and the thalamus was checked for labeled cells. The anterior field A receives its main thalamic input from the ventral nucleus of the MG (MGv). The projection is topographically organized. Roughly, the caudal part of the MGv innervates the rostral part of field A and vice versa. After injection of tracer into low or medium best-frequency sites in A, we also found a topographic gradient along the isofrequency contours: the dorsal (ventral) part of a cortical isofrequency strip receives afferents from the rostral (caudal) portions of the corresponding thalamic isofrequency band. However, it is not so obvious whether such a gradient exists also in the high-frequency part of the projection. A second, weaker projection to field A originates in a magnocellular nucleus that is situated caudomedially in the MG and was therefore named the caudomedial nucleus. The dorsocaudal field DC receives input from the same nuclei as the anterior field, but the location of the labeled cells in the MGv is different. This was demonstrated by injection of different tracers into sites with like best frequencies in fields A and DC, respectively. After injection of HRP into the 1-2-kHz isofrequency strip in field A and injection of Nuclear Yellow (NY) into the 1-2-kHz site in field DC, the labeled cells in the MGv form one continuous array that runs from caudal to rostral over the whole extent of the MGv. The anterior part of this array consists of NY-labeled cells; i.e., it projects to field DC. The caudal part is formed by HRP-labeled cells; i.e., it innervates field A. These findings indicate that there is only one continuous tonotopic map in the MGv. This map is split when projected onto the cortex so that two adjacent tonotopic fields (A and DC) result. The cortical maps are rotated relative to the thalamic map in that rostral portions of the MGv project to caudal parts of the tonotopic cortex and vice versa.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗