Medial geniculate body - an overview (2023)

Medial Genicular Body

Ömedial geniculate bodyIt is the auditory relay center of the thalamus that receives auditory information from the inferior colliculus. It has three divisions: ventral, dorsal and medial.⁸⁰Öventral divisionprojected from the medial geniculate body to the primary auditory cortex, during theback divisionProjects on the auditory association cortex. However, the auditory processing performed by the medial geniculate body is heavily influenced by a plethora of inputs from the auditory cortex, which are thought to outnumber the projections it receives from the midbrain and lower auditory brainstem.⁷¹The medial knee body is thought to play an important role in sound localization and processing of complex voice communication such as human speech.

4.1 Medial Genicular Body (MGB)

Medial Genicular Body

STREET. The cupboard

Ömedial geniculate body(MGB) is a complex of nuclei that receive massive inputs from the IC and therefore serve as important synaptic stations in the pathways for information reaching the auditory areas of the cerebral cortex. MGB nuclei can be distinguished from one another on the basis of cytoarchitecture, chemoarchitecture, tonotopy, connectivity patterns, and acoustic response properties. Neighboring nuclei of the posterior and pulvinar complex also receive auditory stimuli and project to the auditory cortex. The auditory thalamus receives its input from pathways originating in the brainstem nuclei that contribute to the lateral lemniscus, as well as pathways of non-lemniscal origin. The cellular architecture of human GBM is remarkably similar to that of Old World and New World monkeys. Although the relative size and strength of each auditory cortical projection differs from one MGB subdivision to the next, each auditory cortical field receives highly convergent information from a subset of auditory thalamic nuclei, and each auditory thalamic subdivision topographically projects onto a subset of auditory cortical projection auditory nuclei . cortical fields. Thus, like the auditory circuits of the brainstem, the auditory thalamocortical system exhibits extensive convergence and divergence. The tones evoke a characteristic pattern of cortical activation that reflects the projection of the thalamus onto this active site. The earliest electrical response is thought to represent monosynaptic activation of neurons in cortical layers 3 and 4, while later activity represents polysynaptic activation across supragranular cortical layers. In addition to massive upstream input from brainstem and midbrain auditory structures, the MGB also receives significant projection from the areas of the cerebral cortex to which it projects. This reciprocal relationship provides an opportunity for feedback control of the increasing auditory input.

The ventral division (MGBv) exhibits a high degree of tonotopy imposed by the similarly organized ICC entrance. Non-auditory input to the ventral division is derived from the thalamic reticular and ventrolateral medullary nuclei. MGBv projects strongly into the central areas of the auditory cortex, including the primary field. Neurons in the MGBv preserve and transmit to the cortex with high fidelity the temporal and frequency specific properties displayed in the auditory brainstem. In humans, the dorsal division (MGBd) is larger and structurally more heterogeneous than the ventral division. It receives its auditory input mainly from neurons in the pericentral nucleus of the CI. Other afferents arise from the reticular nucleus of the thalamus, the ventrolateral medullary nucleus, the sagul nucleus, the superior colliculus, and the inferior colliculus arm. MGBd neurons, unlike those of MGBv, respond poorly to most sounds and are largely tuned to frequency; Therefore, Tonotopia is not a trademark. The main targets of MGBd neurons are the cortical belt areas. The medial or magnocellular division (mGBM) also exhibits a diverse cellular architecture and primarily receives input from the outer core of the IC. Tonotopia is not a prominent feature of this nucleus, again reflecting the organization of its main afferent source. Neighboring nuclei of the thalamus, including the posterior and pulvinar groups, receive auditory information and send projections to cortical auditory fields.

MGB neurons in all areas appear to retain ITD or IID information extracted at the brainstem level and distribute this information widely to the auditory areas of the cerebral cortex. The neurons of the MGB and cortical auditory fields respond better when the sound source is in the contralateral acoustic hemifield. There is no apparent anatomical specialization of the human MGB for language, nor is there evidence of bilateral asymmetry in MGB size.

Medial geniculate nucleus

The medial geniculate nucleus is the relay core of the auditory pathway. It is inside themedial geniculate body, a rounded elevation lying posteriorly on the ventrolateral surface of the thalamus, and separated from the pulvinar by the arm of the superior colliculus. It receives fibers traveling in the arm of the inferior colliculus. The medial geniculate nucleus contains three main subnuclei, medial (magnocellular), ventral, and dorsal. The forearm separates the medial nucleus, composed of sparse, deeply stained neurons, from the lateral region, composed of medium-sized, densely packed, darkly stained neurons. Laterally, the dorsal nucleus covers the ventral nucleus and extends posteriorly; It is sometimes referred to as the posterior core of the medial knee joint. It contains small to medium-sized light neurons that are less densely packed than those in the ventral nucleus.

The dorsal nucleus receives input from the pericentral nucleus of the inferior colliculus and other brainstem nuclei in the auditory pathway and projects to auditory areas around the primary auditory cortex. Neurons within the dorsal nucleus respond to a wide range of frequencies, and tonotopic representation has not been described in this subdivision. The ventral nucleus receives fibers from the central nucleus of the ipsilateral inferior colliculus through the arm of the inferior colliculus and the contralateral inferior colliculus and projects primarily to the primary auditory cortex. It contains a complete tonotopic presentation: low tones are presented laterally and progressively higher tones are found as the nucleus is traversed from lateral to medial. The medial magnocellular nucleus receives fibers from the inferior colliculus and deep layers of the superior colliculus and diffusely projects to the auditory areas of the cortex and the adjacent insular and opercular fields.

Neurons within the magnocellular subdivision can respond to modalities other than sound, but many cells respond to auditory stimuli, usually over a wider range of frequencies than neurons in the ventral nucleus. Many units show evidence of binaural interaction, with the main effect originating from stimuli in the contralateral cochlea.

Geniculado medial

Ömedial geniculate body(MGB), the thalamic auditory core, receives its ascending auditory inputs from the CI (Abb.25.3). Anatomically, the MGB lies medial and caudal to the much larger visual lateral geniculate nucleus (LGN). In common marmosets, like other non-human primates, the GBM has been subdivided based on cytoarchitecture, myeloarchitectural staining, and calcium-binding proteins.[29]. The large ventral division (MGV) is part of the central lemniscal auditory pathway and receives most of its anatomical input from the central nucleus of the CI. Other divisions include the posterodorsal division (MGPD) found in primates and other mammalian species.[30], an anterior-dorsal division (MGAD) that can only occur in primates[31]and finally the medial (MGM) and suprageniculate (SG) areas, which in other species receive auditory and non-auditory input[30]. These individual areas exhibit unique patterns of thalamocortical connectivity, with the lemniscal MGV projecting to the primary AC, the MGPD projecting to the non-primary AC, and the remaining areas showing broad projections to the primary and non-primary cortices.[29].

Like other areas of the hearing system, the GBM is organized tonotopically. Although such organization has only been demonstrated in squirrel monkeys[32]and other mammalian species, studies by retrograde trackers from AC sites with known frequency tuning suggest similar topography in common marmosets[33]. Neurons within the MGV exhibit typical lemniscal-like responses, including strong frequency-matched responses to narrow-bandwidth stimuli, including tones and the ability to synchronize to tones that change rapidly in time.[34-36]. MGAD neurons have lower frequency specificity and respond equally well to tone- and noise-based stimuli, but are able to reliably synchronize to sounds that vary rapidly in time, much more so than other areas of the MGB. Neurons in the MGPD have very different responses from the other divisions, with many neurons preferring broader band tones, such as bandpass or white noise, and tending to respond to time-varying stimuli with continuous firing, rather than stimulus-synchronized neural activity. Most neurons in the Marmoset MGB also show non-monotonic or tuned responses to different sound intensities. These intensity-matched responses differ significantly from responses observed in the auditory nerve and lower auditory structures, where firing rates increase monotonically with increasing sound intensity.

Fourth order neuron

Ömedial geniculate bodyIt is the main auditory core of the thalamus. Parts of the medial knee joint supposedly serve to direct auditory attention. The medial geniculate body sends signals to the primary auditory cortex, also known as Heschl's transverse temporal gyrus (Brodmann areas 41 and 42), and the auditory association cortex (areas 22 and 52) (Abb. 12-3). The medial knee joint also sends output to the auditory motor cortex, which controls the body's responses to sound. the hearingThe cortex is divided into three areas: a primary area (AI), a secondary area (AII), and a distant projection region (Ep). The researchers have assigned area 42 differently to the primary or secondary auditory cortex. The ventral medial knee joint projects almost entirely onto AI, while the surrounding auditory areas receive projections from the rest of the knee joint body. As with the lower hearing aids, tonotopic relationships are maintained.

Corpo geniculado medial (MG)

The auditory thalamus has long been considered responsible for relaying information to the cerebral cortex, but it is only in the last decade that the functional nature of this structure has received much attention. While previous views tended to reduce thalamic function to a simple relay process, recent research reveals intricate circuitry and a wide variety of membrane properties in resident neurons. It is now clear that the MG is not only a passive transporter of information to the cortex, but is involved in many dynamic processes that significantly change the nature of information (Sherman und Guillery, 1998, 2002). The MG is indeed involved in a variety of functions. These include routine auditory processing (Bartlett et al., 2000; Bartlett and Smith, 1999; Is, 2003; Er und Hu, 2002; Ha, 1995; 2003;Winer et al., 2005; Winer und Larue, 1996) and associated changes in learning and memory (Edeline, 1999, 2003). These complementary roles underscore the importance of the thalamus in the sensory processing hierarchy.

The MG is the last chance to process auditory signals before they reach the auditory cortex. So the MG projects to the AC, which in turn sends back massive projections. In addition, the MG gets its main source of upstream input from the CI. MG-AC connections are reciprocal, but non-reciprocal projections also occur (Plain and Sherman, 2008) and vary such that each subdivision has a distinct pattern of connection with other structures. Additional inputs come from the thalamic reticular nucleus and, to a lesser extent, the lower auditory nuclei, including the SOC, NLL, and CNC. Ascending fibers enter the structure medially through the CI arm and terminate between neurons in each subdivision. Connections to the auditory cortex pass through the posterior branch of the inner capsule.

The main source of input for the MGV is the ipsilateral CIC (Abb. 24.1). IC projections to MGV appear to be from glutamatergic and GABAergic neurons.Bartlett und Smith, 1999). The main projection from the MGV to the auditory cortex terminates mainly in layers III and IV of the primary auditory cortex (Abb. 24.1). The tonotopic organization of the projection is preserved in the primary fields.

The dorsal division of the MG has larger cell bodies, particularly at the more dorsal and medial sites. MGD shows no obvious packing arrangements of neurons. The largest neurons in the medial portions of the MGD probably represent the suprageniculate nucleus.Llano and Sherman, 2008,). MGD shows strong somatic staining for calbindin and weak neuropil staining for parvalbumin (Fig. 24.11 and 24.12). Several cell types have been described in the MGD. Ray cells are the most numerous, with radially symmetric dendritic arrays and a simple branching pattern. Tuft cells are also present in significant numbers (Abb. 24.11). These cells tend to organize into thin layers, particularly dorsolaterally, with dendritic spines extending from each pole (Winer and others, 1999). A secondary population of small stellate cells was also recognized. Most MGD neurons respond to acoustic stimulation with a wide range of latencies, typically longer than MGV neurons, and exhibit broader frequency tuning. The tonotopic organization in the MGD is not apparent in the records of any species.

The main sources of ascending auditory inputs for the MGD are the DCIC and the LCIC (Abb. 24.1;Jones, 2007; Lee und Sherman, 2009; Malmierca, 2003). These entries represent glutamatergic and GABAergic neurons.Bartlett und Smith, 1999). MGD projects primarily to the non-primary (girdle) areas of the auditory cortex where tonotopy is weak or absent.EU.).

The medial division of the MG borders MGV and MGD medially and extends from the rostral to the caudal pole of the MG.Fig. 24.11 and 24.12). AlthoughRecognized as a single division, the MGM is quite heterogeneous in terms of cell types and connectivity. The MGM shows a loose packing arrangement with some very large cells. Similar to MGD, MGM shows strong somatic staining for calbindin and weak neuropil staining for parvalbumin (Abb. 24.12;Plano and Sherman, 2008, 2009; Lou and others). The MGM contains the largest neurons in the MG and a variety of different cell types have also been identified.Winer and others, 1999). Some neurons are calbindin-responsive and project mainly to cortical layers I and II, while others immunostain calbindin and parvalbumin and project to the intermediate layers.Jones, 2007). Response properties in MGM neurons are highly variable and consistent with the different classes of neurons that populate the MGM. Some neurons are tightly tuned to frequencies with short latencies, similar to MGV neurons, while others are broadly tuned and have longer latencies.

Inputs to the MGM include both auditory and non-auditory sources (Ryugo and Weinberger, 1978; Vepsic, 1966). The main acoustic inputs come from CNC and ECIC as well as from CN, SOC and VLL (Malmierca et al., 2002). The MGM also projects to the corpus striatum and amygdala (LeDoux et al., 1985; Ryugo und Killackey, 1974). Non-auditory inputs include the deep layers of the superior colliculus and other somatosensory, vestibular, visual, and nociceptive stimuli.Jones, 2007).

In addition to the prototypical major auditory thalamic nuclei, many other thalamic cells project into higher-order nuclei on layer 1 of the neocortex or on other subcortical structures such as the basal ganglia or the amygdala.Cheatwood and others, 2003). This projection pattern is particularly common in neurons in the intralaminar nuclei and the adjacent "paralaminar" nuclei.Herkenham, 1980), such as the suprageniculate nucleus, posterior intralaminar and peripeduncular (Fig. 24.11 and 24.12;Clugnetet al., 1990; Ryugo und Killackey, 1974). The degree of this heterogeneity is reflected in different distributions of calcium-binding proteins.Lu and others, 2009).

3.3.3 The auditory thalamus and cortex

The auditory thalamus (AGB) contains ventral, dorsal, and medial divisions. The ventral MGB (MGBv) only receives input from the ICC. Its neurons respond with short latencies, creating a tonotopic map. In contrast, dorsal MGB neurons (MGBd) respond poorly to auditory stimuli; its inputs are derived solely from the ventral medial border of the ICX. The magnocellular region of the MGB (mGBM) is the multisensory division of the auditory thalamus. It is analogous to the ICX with wider frequency-tuning characteristics, receiving non-auditory input originating from the ICX and a direct path from the DCN and GCD region bypassing the IC (Schofield and others, 2014). The mGBM's multisensory inputs include somatosensory afferents from the spinal-thalamic, dorsal, and trigeminal columns, as well as visual afferents from the SC. Multisensory responses in MGBm have been documented (Wu and others, 2015).

In the auditory cortex, as in subcortical structures, multisensory integration is mediated by neurons that are independently activated by more than one sensory input. Furthermore, neurons in a given cortical area may be activated by a single modality, but their responses are significantly modulated, i.e., enhanced or suppressed, by the input of a second modality.Trash et al. (2012) investigated the effects of multisensory plasticity-inducing stimulation on the somato-auditory integration of neurons simultaneously recorded in DCN and A1. The immediate (bimodal response) and long-lasting (bimodal plasticity) effects of Sp5 sound stimulation were facilitation or suppression of sound-evoked firing rates in DCN and A1. These relief or suppression effects lasted up to an hour.

Nava et al. (2014)tested congenital and late-deaf CI recipients, paired by age with two groups of auditory controls, in an auditory-tactile redundancy paradigm, measuring response times to unimodal and transmodal redundant stimuli. It was shown that both congenital and late deaf CI recipients were able to integrate tactile audio stimuli. This suggestedNava et al. (2014)that congenital and acquired deafness do not impede the development and recovery of basic multisensory processing.

Interactions between the auditory and somatosensory systems play an important role in enhancing the human experience during dynamic contact between the hands and the environment.Cake Book et al., 2014). They found that cross-modal cortical activity mediates preferential responses from the cortical area that processes more pronounced stimuli and an inhibition of cortical activity in the area that processes less pronounced stimuli. In addition, vibrotactile stimuli and non-vibratory tactile stimuli activate the auditory girdle area in animals and humans (Fu et al., 2003; Schumann and others, 2006) mit supraadditiver Integration (Kayser and others, 2005).

III.B Responsiveness of neuronal populations of the medial geniculate body to vocalizations

The neuronal responses in guinea pig MGB are similar to those in CI in many respects; However, there are also some notable differences (Šuta et al., 2007). A comparison of the spectrograms of the calls with the spectrotemporal response maps (only neurons from the ventral part of the MGB were analyzed) revealed, similar to the CI, that the patterns present in the population response maps corresponded to many features of the acoustics of a song standard (Figure 2). However, there were also some notable differences.Abb. 2bshows, for example, that high CF (CF ≥ 8 kHz) MGB neurons show increased activity at the onset of the whistle (140–250 ms after stimulus onset), despite the absence of energy in that frequency range. Another difference becomes apparent from a comparison of Chutter's spectrotemporal map (Abb. 2c) and the spectrogram of that call, where the duration of the response to each session of the call is shorter than the duration of the sessions themselves.

Population PSTHs of MGB neurons reflect the temporal acoustic envelopes as shown in FIGAbb. 3. When acoustic envelope and PSTH population are correlated, the highest correlation is for chirp (r = 0.94), the lowest for purr (r = 0.65) and for chutter (r = 0.57). A specific relationship becomes apparent when the sound envelope of a whistle is compared to its PSTH population. The dominant element in the response is the initial response, which contrasts with the weak energy at the beginning of the whistle. In this context, the low correlation between the call envelope and the PSTH population is mainly due to the phasic character of the neural response of the MGB neurons, which is already present for simple acoustic stimuli such as tone bursts or noise (Kvasňák et al., 2000). The early onset response in the PSTH whistling population is generated by the response of high frequency neurons to the low frequency portion of the whistling spectrum (Šuta et al., 2007). When stimulated by a low-pass filtered whistle, high-CF MGB neurons responded vigorously compared to a weak response to a high-pass filtered whistle. Therefore, the early onset response is really a response to the low frequency component of the whistle, although this frequency range is well below neural CF.

The connection between the spectral properties of the calls and the firing of MGB neurons can be seen by comparing the CF frequency profiles with the short-duration sound spectrum. As in the case of IC neurons, rate CF profiles are shown for the first timeAbb. 4for the three consecutive parts of the whistle (a-c), for purr (d), chirp (e) and chatter (f). In the first 110 ms of the signal tone, the correlation coefficient between the short-term spectrum and the frequency-relevant HR profile is 0.48. The CF frequency profile reflects the dominant spectral component of the first harmonic (fundamental) and second harmonic (1–4 kHz) frequencies, but these two frequencies are not separated. A second peak appears in the 5 to 9 kHz range, although at this point there is almost no energy in the sound above 7 kHz. In the middle part of the whistle, the correlation coefficient is 0.56. The dominant (fundamental) first harmonic and second harmonic frequencies produce the strongest firing of neurons with corresponding FCs. Higher harmonic frequencies are reflected in a flat, weak rate profile. The last part of the whistle shows the weakest correlation coefficient (r = 0.28); the CF frequency profile is flat due to weak neural activity at the end of the whistle. Purr, chirp and kick (Abb. 4d-f), some local spectral peaks in the rate CF profile are enhanced and produce dominant elements, while other frequencies are not reflected. In general, the values ​​of the correlation coefficients between the sound spectra and the CF frequency profiles are low (purr: r = 0.10; chirp: r = 0.30; chutter: r = 0.11).

A direct comparison of the IC and MGB data suggests that the representation of the spectral features found at the IC level is preserved in the MGB for broadband calls (whistle, chirp); However, this representation is less accurate for low frequency calls (Chutter, Purr). Several studies have shown that the encoding of a vocalization spectrum cannot be described by a simple linear model. For example,Laut Yeshurun ​​et al. (1989)concluded from their study of awake squirrel monkeys that some of the MGB cell responses to natural vocalizations could be predicted by assuming a linear transformation function, while other responses could be predicted by nonlinear (second-order) nuclei.Tanaka and Taniguchi (1991)similarly concluded that most neurons in the guinea pig MGB showed firing patterns that were unpredictable from the spectral energy of the call near the neuronal CF. Made an interesting contribution to the problem of vocalization processing in the mammalian auditory systemPhilibert and AI. (2005)who compared the responses of MGB neurons in guinea pigs and rats. They found that neurons in guinea pig and mouse MGB showed similar response strengths to guinea pig vocalizations and showed no preference for the natural pattern over time-reversed versions of the calls in either species. This discovery led them to conclude that in mammals, selectivity for the natural version of species-specific vocalizations is expressed only at the cortical level.

As suggested byCreutzfeldet al. (1980). There are significant differences in the encoding of vocalizations between the MGB and the auditory cortex. The thalamocortical transformation in the temporal and spectral domain has been studied byMueller and others. (2002). Simultaneously, they recorded responses from neurons in the ventral division of themedial geniculate bodyand in the cat's primary auditory cortex. The spectrotemporal receptive fields of individual units were deduced as they approached by dynamic wave motions. They found similar spectral integration, as measured by excitatory bandwidth and spectral modulation preference, while temporal modulation rates in the cortex were a factor of two lower (with the upper limit of the temporal modulation function in the thalamus being 62.9 Hz and in the thalamic cortex 37, 4Hz). There was no apparent correlation between spectral and temporal integration properties, suggesting that excitatory-inhibitory interactions are largely independent.