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T Bonhoeffer

Publications and source records attributed to T Bonhoeffer.

31 records · Page 2Linked to original sources
PubMed1995

Optical imaging of intrinsic signals as a tool to visualize the functional architecture of adult and developing visual cortex.

One of the most common principles of cortical organization is that neurons with similar response properties are clustered together in space. Thereby the environment is represented in an orderly fashion on the cortical surface in a so-called "cortical map". In primary visual cortex, for instance, neurons with similar orientation preferences are grouped together, forming the orientation preference map. Optical imaging of intrinsic signals allows to investigate the organization of such maps in vivo. Neuronal activity was measured utilizing the fact that the transition from oxy-hemoglobin to hemoglobin in active brain areas can be detected optically by recording changes in light reflectance with a high resolution CCD-camera. When using this technique to look at the exact patterning of orientation preference maps in cat visual cortex a novel principle for the organization of cortical maps was observed: orientation was not organized in parallel bands as had previously been thought but iso-orientation domains were organized radially; orientations from 0 to 180 degrees were laid out in a pinwheel-like fashion around singularities which we termed "orientation-centers". After observing pinwheel patterns in orientation preference maps in adult cat visual cortex it was also investigated how these meticulously arranged maps develop in the cortex of young kittens. Performing chronical recordings in kittens from the age of postnatal day 17 on we were able to observe how orientation maps form already during the third week of life and--under normal conditions--remain largely unchanged thereafter.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Relationship between lateral inhibitory connections and the topography of the orientation map in cat visual cortex.

The functional and structural topography of lateral inhibitory connections was investigated in visual cortical area 18 using a combination of optical imaging and anatomical tracing techniques in the same tissue. Orientation maps were obtained by recording intrinsic signals in regions of 8.4-19 mm2. To reveal the inhibitory connections provided by large basket cells, biocytin was iontophoretically injected at identified orientation sites guided by the pattern of surface blood vessels. The axonal and dendritic fields of two retrogradely labelled large basket cells were reconstructed in layer III. Their axonal fields extended up to 1360 microns from the parent somata. In addition to single basket cells, the population of labelled basket cell axons was also studied. For this analysis anterogradely labelled basket axons running horizontally over 460-1280 microns from the core of an injection site in layer III were taken into account. The distribution of large basket cell terminals according to orientation preferences of their target regions was quantitatively assessed. Using the same spatial resolution as the orientation map, a frequency distribution of basket cell terminals dependent on orientation specificity could be derived. For individual basket cells, the results showed that, on average, 43% of the terminals provided input to sites showing similar orientation preferences (+/- 30 degrees) to those of the parent somata. About 35% of the terminals were directed to sites representing oblique-orientation [+/- (30-60) degrees], and 22% of them terminated at cross-orientation sites [+/- (60-90) degrees]. Furthermore, the possible impact of large basket cells on target cells at different distances and orientation preferences was estimated by comparing the occurrence of orientation preferences with the occurrence of basket terminals on the distance scale. It was found that a basket cell could elicit iso-orientation inhibition with a high impact between 100-400 and 800-1200 microns, strong cross-orientation inhibition at approximately 400-800 microns, and oblique-orientation inhibition between 300-500 and 700-900 microns from the parent soma. The non-isotropic topography of large basket axons suggests a complex function for this cell class, possibly including inhibition related to orientation and direction selectivity depending on the location of the target cells and possible target selectivity.

Animals↗
PubMed1994

Reverse occlusion leads to a precise restoration of orientation preference maps in visual cortex.

In the visual system of young kittens, the layout of the cortical maps for ocular dominance and orientation preference converges to an equilibrium state within the first few weeks of life and normally remains largely unchanged. If during the critical period, however, patterned visual experience is restricted to only one eye for a few days, cortical neurons lose their ability to respond to stimulation of the deprived eye. We used the 'reverse occlusion' protocol together with chronical optical imaging to investigate how the profound anatomical changes accompanying monocular deprivation affect the spatial pattern of the cortical orientation preference map. We report here that after 1 week of monocular deprivation, cortical orientation maps for the deprived eye had vanished. But we also discovered that after subsequent reverse occlusion the restored orientation maps were very similar to the original maps. This demonstrates that in spite of functional disconnection of one eye after monocular deprivation, the layout of cortical orientation maps, when re-established for this eye, is not formed from scratch but is strongly influenced by previous experience.

Animals↗
PubMed1993

The layout of iso-orientation domains in area 18 of cat visual cortex: optical imaging reveals a pinwheel-like organization.

In this study we used optical imaging based on activity-dependent intrinsic signals to determine the distribution of cells responding to gratings of various orientations moving in different directions in area 18 of cat visual cortex. To test directional-selective clustering of neurons, we compared cortical activity maps obtained by stimulation with two gratings of identical orientation but moving in opposite directions. We found those maps to be almost identical, suggesting that neurons are not notably clustered into directionality columns. We also compared activity maps obtained with gratings of different orientations. Each of the orientation maps was similar to the 2-deoxyglucose maps previously reported. Having compiled the information obtained from the different orientations into one "orientation preference map," we found, in contrast to earlier reports, that iso-orientation domains are not elongated parallel bands but are small patches organized in "pinwheels" around points that we refer to as "orientation centers." We furthermore show that the only locations at which orientation preference changes rapidly are these orientation centers and not lines or loops. In addition, this report clarifies that our observations on the functional architecture of cat area 18, although at first sight at variance with earlier observations, are actually fully consistent with them. We therefore propose that in cat visual cortex pinwheel-like patterns of orientation preference form an irregular mosaic of modular units with an average density of 1.2 pinwheels per square millimeter.

Animals↗
PubMed1991

Iso-orientation domains in cat visual cortex are arranged in pinwheel-like patterns.

The mammalian cortex is organized in a columnar fashion: neurons lying below each other from the pia to the white matter usually share many functional properties. Across the cortical surface, cells with similar response properties are also clustered together, forming elongated bands or patches. Some response properties, such as orientation preference in the visual cortex, change gradually across the cortical surface forming 'orientation maps'. To determine the precise layout of iso-orientation domains, knowledge of responses not only to one but to many stimulus orientations is essential. Therefore, the exact depiction of orientation maps has been hampered by technical difficulties and remained controversial for almost thirty years. Here we use in vivo optical imaging based on intrinsic signals to gather information on the responses of a piece of cortex to gratings in many different orientations. This complete set of responses then provides detailed information on the structure of the orientation map in a large patch of cortex from area 18 of the cat. We find that cortical regions that respond best to one orientation form highly ordered patches rather than elongated bands. These iso-orientation patches are organized around 'orientation centres', producing pinwheel-like patterns in which the orientation preference of cells is changing continuously across the cortex. We have also analysed our data for fast changes in orientation preference and find that these 'fractures' are limited to the orientation centres. The pinwheels and orientation centres are such a prominent organizational feature that it should be important to understand their development as well as their function in the processing of visual information.

Animals↗
PubMed1990

Formation of target-specific neuronal projections in organotypic slice cultures from rat visual cortex.

A characteristic feature of the mammalian cortex is that projection neurons located in distinct cortical layers send their axons to different targets. In visual cortex, cells in layers 2 and 3 project to other cortical areas, whereas cells in layers 5 and 6 project to subcortical targets such as the lateral geniculate nucleus. The proper development of these projections is crucial for correct functioning of the visual system. Here we show that specific connections are established in an organotypic culture system in which rat visual cortex slices are co-cultured with another slice of the visual cortex or with a thalamic slice. The laminar origin and cellular morphology in vitro of cortical projections to other cortical regions or to subcortical targets are remarkably similar to those seen in vivo. In addition, axons of projecting cells are not restricted to particular pathways, but appear instead to grow directly towards their appropriate target. These observations raise the possibility that chemotropic attraction from the target areas may play an important part in the development of the cortical projection pattern.

Afferent Pathways↗
PubMed1990

Non-Hebbian synapses in rat visual cortex.

In the mammalian CNS, long term potentiation can be induced by repeatedly pairing presynaptic stimulation with postsynaptic depolarization of a single cell, similar to a model proposed by Hebb, that synaptic strengthening occurs as a result of correlated pre- and postsynaptic activity. However, our experiments indicate that the Hebbian rule is not strictly valid in the cortex. Double intracellular recordings showed that synaptic reinforcement is not confined to the depolarized postsynaptic neuron, but is also observed in adjacent but not coactivated neurons. The enhancement and its spread is stimulus-specific, it occurs only for fibres stimulated during the pairing procedure. During development, this spread might lead to a characteristic organizing principle of the cortex, the clustering of cells with similar functional properties.

Animals↗
PubMed1989

Cellular organization and development of slice cultures from rat visual cortex.

Slice cultures from the visual cortex of young rats were prepared using the roller culture technique (Gähwiler 1984). After 10 days in vitro the cortical cultures flattened to 1-3 cell layers, surviving for up to 12 weeks. The cultures were organotypically organized, the typical layered structure of the cortex was preserved. The neuronal composition of slice cultures was studied using intracellular staining, Golgi impregnation and GABA immunohistochemistry. Both pyramidal cells and several types of nonpyramidal cells were identified in the slice cultures. Electrophysiological recordings showed that the electrical properties of cells in culture were similar to those measured in acute slice preparations; for some cells, however, the spontaneous activity was higher. The maintained activity was strongly increased by application of the GABA antagonist bicuculline and decreased by GABA, suggesting that GABAergic inhibition is present in these preparations. We could observe the postnatal maturation of some characteristic morphological features in culture. For example, pyramidal cells in 6 day-old rats in situ have very short basal dendrites with growth-cones, and the dendrites are free of spines. After 2-3 weeks in culture growth-cones were no longer observed. Instead, the cells had developed a large basal dendritic field and the dendrites were covered with spines. Slice cultures therefore may provide a useful tool for physiological, anatomical, pharmacological and developmental studies of cortical neurons in an organotypical environment.

Action Potentials↗
PubMed1989

Synaptic plasticity in rat hippocampal slice cultures: local "Hebbian" conjunction of pre- and postsynaptic stimulation leads to distributed synaptic enhancement.

A central theme in neurobiology is the search for the mechanisms underlying learning and memory. Since the seminal work, first of Cajal and later of Hebb, the synapse is thought to be the basic "storing unit." Hebb proposed that information is stored by correlation: synapses between neurons, which are often coactive, are enhanced. Several recent findings suggest that such a mechanism is indeed operative in the central nervous system. Pairing of activity on presynaptic fibers with strong postsynaptic depolarization results in synaptic enhancement. While there is substantial evidence in favor of a postsynaptic locus for detection of the synchronous pre- and postsynaptic event and subsequent initiation of synaptic enhancement, the locus of this enhancement and its ensuing persistence is still disputed: both pre- and postsynaptic contributions have been suggested. In all previous studies, the enhancement was presumed to be specific to the synapses where synchronous pre- and postsynaptic stimulation was applied. We report here that two recording techniques--optical recording, using voltage-sensitive dyes, and double intracellular recordings--reveal that synaptic enhancement is not restricted to the stimulated cell. Although we paired single afferent volleys with intracellular stimulation confined to one postsynaptic cell, we found that strengthening also occurred on synapses between the stimulated presynaptic fibers and neighboring cells. This suggests that synaptic enhancement by the "paired-stimulation paradigm" is not local on the presynaptic axons and that, in fact, the synapses of many neighboring postsynaptic cells are enhanced.

Animals↗
PubMed1988

Optical recording with single cell resolution from monolayered slice cultures of rat hippocampus.

Voltage-sensitive dyes were used to optically record the membrane potentials from neurons in hippocampal slice cultures. Multi-channel recordings from these monolayered but otherwise 'organotypic' slice cultures had very good spatial as well as good temporal resolution (15 x 15 micron, 0.5 ms respectively). We show that in this preparation action potentials elicited by intracellular current pulses can be recorded optically and that single spikes are readily detectable without averaging. Furthermore, a new procedure which significantly reduces photodynamic damage is described. Our study demonstrates the feasibility of optical recording with single cell resolution in an organotypic mammalian CNS preparation.

Animals↗
PubMed1984

Parallel processing for associative and neuronal networks.

We represent a parallel processing network, consisting of nine microcomputers, for neuron-network simulations and for the realization of an associative computer memory. We add some remarks on the present possibilities to implement larger associative networks and on parallel processing strategies in general.

Association↗