Journal: Journal of Cerebral Blood Flow & Metabolism

Article Title: From unspecific to adjusted, how the BOLD response in the rat hippocampus develops during consecutive stimulations

doi: 10.1177/0271678X16634715

Figure Lengend Snippet: Summary of the applied stimulation protocols. During all experiments, the perforant pathway was stimulated with 20 consecutive stimulation trains. The first stimulation train (indicated by red boxes) was applied 2 min after starting fMRI. Each stimulation train lasts for 8 s and was followed by 52 s rest (indicated by the gray boxes). During the first set of experiments, continuous 1, 5, 10, or 20 Hz pulses were applied during each stimulation train. During these stimulation frequencies, each applied pulse elicited one population spike; consequently, under these conditions, the input (i.e. applied pulses) and output activity (number of population spikes) vary in a similar way (Experiment 1). In a second set of experiments, high frequency pulses (5, 10, or 20) were superimposed on a 1 Hz stimulation protocol. Because only one population spike was generated to the first pulse of the burst during these conditions, whereas all subsequent pulses only generated fEPSPs, the number of population spikes was similar. Consequently, only the incoming activity varied, whereas the output activity remained similar (Experiment 2). During the third set of experiments, the perforant pathway was additionally stimulated with 5 Hz-4 pulses and 10 Hz-2 pulses; thus, there were four different experimental conditions in which 20 pulses were applied but different numbers of population spikes were generated (Experiment 3).

Article Snippet: To stimulate the hippocampal formation, a bipolar stimulation electrode (114 μm in diameter, Teflon-coated tungsten wire, A-M Systems) was placed into the perforant pathway (AP: −6.9 mm; ML + 4.1 mm from Bregma; DV 2.3–3.0 mm from dural surface) of the right hemisphere, according to the atlas of Paxinos and Watson.

Techniques: Activity Assay, Generated

Journal: Journal of Cerebral Blood Flow & Metabolism

Article Title: From unspecific to adjusted, how the BOLD response in the rat hippocampus develops during consecutive stimulations

doi: 10.1177/0271678X16634715

Figure Lengend Snippet: Summary of the measured BOLD responses in the right hippocampus during electrical stimulation of the right perforant pathway. Here, averaged maximal BOLD signal intensities during each BOLD response measured in experiment 1 (a), experiment 2 (b), and experiment 3 (c) are depicted. The averaged BOLD response during the first, fourth, and 18th–20th stimulation trains are summarized on the right. Asterisks indicate significantly increased BOLD response during train 4 when compared with train 1 (black: 20 Hz-1-pulse, dark blue: 1 Hz-50-pulse, turquoise: 10 Hz-2-pulse).

Article Snippet: To stimulate the hippocampal formation, a bipolar stimulation electrode (114 μm in diameter, Teflon-coated tungsten wire, A-M Systems) was placed into the perforant pathway (AP: −6.9 mm; ML + 4.1 mm from Bregma; DV 2.3–3.0 mm from dural surface) of the right hemisphere, according to the atlas of Paxinos and Watson.

Techniques:

Journal: Journal of Cerebral Blood Flow & Metabolism

Article Title: From unspecific to adjusted, how the BOLD response in the rat hippocampus develops during consecutive stimulations

doi: 10.1177/0271678X16634715

Figure Lengend Snippet: Summary of the electrophysiological responses in the right dentate gyrus during electrical stimulation of the right perforant pathway. Here, averaged population spike amplitudes during individual stimulus trains recorded in experiment 1 (a), experiment 2 (b), and experiment 3 (c) are depicted. The development of individual population spike amplitudes during the first, fourth, and 18th–20th stimulation trains are summarized on the right.

Article Snippet: To stimulate the hippocampal formation, a bipolar stimulation electrode (114 μm in diameter, Teflon-coated tungsten wire, A-M Systems) was placed into the perforant pathway (AP: −6.9 mm; ML + 4.1 mm from Bregma; DV 2.3–3.0 mm from dural surface) of the right hemisphere, according to the atlas of Paxinos and Watson.

Techniques:

Journal: Journal of Cerebral Blood Flow & Metabolism

Article Title: From unspecific to adjusted, how the BOLD response in the rat hippocampus develops during consecutive stimulations

doi: 10.1177/0271678X16634715

Figure Lengend Snippet: The relation between spiking activity (i.e. averaged population spike amplitude, see Figure 3) and the resultant BOLD response (see Figure 2) depends on the applied stimulation pattern. Strong correlations between these two factors were only found after an initial default-like BOLD response (i.e. induced by the first stimulation train, red dot) and followed by a short period of functional reconfiguration (train 2–4, pale dots). During stimulation with ≥ 10 high-frequency burst pulses, this correlation is nonexistent.

Article Snippet: To stimulate the hippocampal formation, a bipolar stimulation electrode (114 μm in diameter, Teflon-coated tungsten wire, A-M Systems) was placed into the perforant pathway (AP: −6.9 mm; ML + 4.1 mm from Bregma; DV 2.3–3.0 mm from dural surface) of the right hemisphere, according to the atlas of Paxinos and Watson.

Techniques: Activity Assay, Functional Assay

Journal: Journal of Cerebral Blood Flow & Metabolism

Article Title: From unspecific to adjusted, how the BOLD response in the rat hippocampus develops during consecutive stimulations

doi: 10.1177/0271678X16634715

Figure Lengend Snippet: Distribution of significantly activated voxels depends on the actual stimulation protocol. The applied stimulation protocol does not only determine the consistency of significant BOLD responses between early (i.e. train 5–11) and late (i.e. train 14–20) trains, but also the spatial distribution.

Article Snippet: To stimulate the hippocampal formation, a bipolar stimulation electrode (114 μm in diameter, Teflon-coated tungsten wire, A-M Systems) was placed into the perforant pathway (AP: −6.9 mm; ML + 4.1 mm from Bregma; DV 2.3–3.0 mm from dural surface) of the right hemisphere, according to the atlas of Paxinos and Watson.

Techniques:

Journal: Journal of Cerebral Blood Flow & Metabolism

Article Title: From unspecific to adjusted, how the BOLD response in the rat hippocampus develops during consecutive stimulations

doi: 10.1177/0271678X16634715

Figure Lengend Snippet: Application of an alternative stimulation protocol affects the development of BOLD responses to low frequency (5 Hz, green color) but not to high-frequency (1 Hz-20-pulse, blue color) stimulation. (a) Left panel: BOLD time series measured during alternate stimulations starting with a 5 Hz (protocol 1, top) or a 1 Hz-20-pulse (protocol 2, bottom) protocol. Middle panel: Summary of individual BOLD responses during stimulation and their respective decline over time (calculate between trains 5 and 20). Right panel: Averaged BOLD responses to 5 Hz and 1 Hz-20-pulse stimulation (between trains 5 and 20). (b) Left panel: BOLD time series measured during repetitive 5 Hz- and 1 Hz-20-pulse stimulations. Middle panel: Decline of BOLD responses during repetitive stimulations; top graph depicts all measuring points that correspond to protocol 1 and the lower graph depicts all measuring points that correspond to protocol 2. Right panel: average BOLD responses calculated from all responses between trains 5 and 20). (c) Comparison of BOLD responses observed during application of alternating or single stimulation protocols. An asterisk indicates a significant difference.

Article Snippet: To stimulate the hippocampal formation, a bipolar stimulation electrode (114 μm in diameter, Teflon-coated tungsten wire, A-M Systems) was placed into the perforant pathway (AP: −6.9 mm; ML + 4.1 mm from Bregma; DV 2.3–3.0 mm from dural surface) of the right hemisphere, according to the atlas of Paxinos and Watson.

Techniques: Comparison

Journal: Journal of Cerebral Blood Flow & Metabolism

Article Title: From unspecific to adjusted, how the BOLD response in the rat hippocampus develops during consecutive stimulations

doi: 10.1177/0271678X16634715

Figure Lengend Snippet: BOLD responses and the underlying alterations in neuronal activities.

Article Snippet: To stimulate the hippocampal formation, a bipolar stimulation electrode (114 μm in diameter, Teflon-coated tungsten wire, A-M Systems) was placed into the perforant pathway (AP: −6.9 mm; ML + 4.1 mm from Bregma; DV 2.3–3.0 mm from dural surface) of the right hemisphere, according to the atlas of Paxinos and Watson.

Techniques: Activity Assay, Activation Assay