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Figure from:The neuroscience of tinnitus

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Figure 2. Normal and reorganized tonotopic maps in primary auditory cortex (Al). (a) The characteristic frequency at each recording site is color-coded and overlaid on a photograph of the cortical surface for a control cat (i) and a cat with a noise induced hearing loss (ii). The hearing loss was limited to frequencies > 10 kHz and amounted to 3 dB at 12 kHz, 12 dB at 16 kHz, 22 dB at 24 kHz and 23 dB at 32 kHz. (244 and 245 are cat identification numbers.) (b) The effect of restricted high-frequency hearing loss on the input to pyramidal cells (numbered 1-13) in auditory cortex. The large colored arrow shows the normal frequency gradient of the inputs conveying the tonotopic mapping. The thin vertical lines leading to the cortical cells are color-coded to reflect their frequency-specific input from the thalamus. For the higher frequencies, covering the range of the hearing loss, the lines are shown as dashed to indicate their reduced ability to activate cortical cells at low stimulus levels and during silence. Numerous divergent connections lead from each thalamic cell to a range of cortical cells (indicated by lines with the same color). A few inhibitory feedforward connections are indicated [one is labeled (i) on the left]. These affect the same cells that receive their thalamic inputs. Feedback inhibition is also prevalent but is only shown for cell 1 (ii). The assumption is that loss of input limits not only the excitation but also, even more strongly, the inhibitory feedforward activity. As a result, the diverging thalamic inputs from neighboring unaffected cells, and the inputs from cortical cells via horizontal fibers, face less competition from inhibition at those cortical cells deprived from thalamic input. Thus, these excitatory inputs are disinhibited or ‘unmasked’ and can impose their own frequency-selective inputs on cortical cells in the hearing loss range, which will ultimately result in a reorganization of the tonotopic map in the hearing-loss animal. Abbreviations: AES, anterior ectosylvian sulcus; PES, posterior ectosylvian sulcus.

Figure 2 Normal and reorganized tonotopic maps in primary auditory cortex (Al). (a) The characteristic frequency at each recording site is color-coded and overlaid on a photograph of the cortical surface for a control cat (i) and a cat with a noise induced hearing loss (ii). The hearing loss was limited to frequencies > 10 kHz and amounted to 3 dB at 12 kHz, 12 dB at 16 kHz, 22 dB at 24 kHz and 23 dB at 32 kHz. (244 and 245 are cat identification numbers.) (b) The effect of restricted high-frequency hearing loss on the input to pyramidal cells (numbered 1-13) in auditory cortex. The large colored arrow shows the normal frequency gradient of the inputs conveying the tonotopic mapping. The thin vertical lines leading to the cortical cells are color-coded to reflect their frequency-specific input from the thalamus. For the higher frequencies, covering the range of the hearing loss, the lines are shown as dashed to indicate their reduced ability to activate cortical cells at low stimulus levels and during silence. Numerous divergent connections lead from each thalamic cell to a range of cortical cells (indicated by lines with the same color). A few inhibitory feedforward connections are indicated [one is labeled (i) on the left]. These affect the same cells that receive their thalamic inputs. Feedback inhibition is also prevalent but is only shown for cell 1 (ii). The assumption is that loss of input limits not only the excitation but also, even more strongly, the inhibitory feedforward activity. As a result, the diverging thalamic inputs from neighboring unaffected cells, and the inputs from cortical cells via horizontal fibers, face less competition from inhibition at those cortical cells deprived from thalamic input. Thus, these excitatory inputs are disinhibited or ‘unmasked’ and can impose their own frequency-selective inputs on cortical cells in the hearing loss range, which will ultimately result in a reorganization of the tonotopic map in the hearing-loss animal. Abbreviations: AES, anterior ectosylvian sulcus; PES, posterior ectosylvian sulcus.

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