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What & where in the auditory pathway - Coggle Diagram
What & where in the auditory pathway
theoretical background
known separate what / where pathways in the visual system
what - ventral
where - dorsal
empirical evidence
Romanski_1999
demonstration of two pathways oriniginating in separate non-primary cohcleotopic auditory fields (laurel belt region - AL and CL) projecting to to distinct regions of the frontal lobes - using a combination of electrophysiological recording and anatomical tracing
CL to caudal dorsolateral prefrontal cortex
AL to rostral and ventral prefrontal areas
dorsal and ventral prefrontal areas are associated to spatial and non-spatial functional domains respectively
possible interpretation: caudal auditory belt - dosa PFC and rostral auditory belt - ventral PFC form distinct what and where pathways similar to visual streams
relation to general theories of frontal lobe organization:
functional domain hypothesis: frontal lobe organization into separate dorsolateral spatial and ventrolateral object-processing areas
difference in connectivity between anterior and posterior belt/parabelt connectivity to thalamus and cortical regions
Alain_2001
task-related effects on ERP's seen in anterior and posterioir brain regions beginning at 300ms lasting for several hundred milliseconds
location processing generated greater activation posterioir temporal cortex, parietal cortex and superior frontal sulcus
relative to location, pitch processing generated greater activation in auditory cortex and inferior frontal gyrus
similarity between prefrontal areas activated during sound identity and sound location processing and those activated in visual processing
organization into what and where information processing might reflect a fundamental cortical organization principle
methods to study in animals and humans
Romanski_1999
methods:
micro electrode recordings in the lateral belt region in macaque (N = 4)
best center frequency at each recording site was determined
frequency reversals identified cochleotopic boundaries of those fields
four to six distinguishable anatomical tracers were injected into AL, ML, CL (lateral belt)
both anterograde and retrograde tracers
in two of N = 4, one different tracer was injected in same frequency region of all three fields to look into interaction between frequency and region (light grey shaded area in DU - 2 kHz and C17 - 4 - 8 kHz)
why the electrophysiological recording? discussion question
to combine purely anatomical studies with functional localisation of separate belt areas as origins of possible auditory streams
results:
connections to frontal lobe, topographically organised:
CL
caudal principal sulcus (area 46)
caudal inferior convexity (areas 12 vl and 45)
dorsal periarcuate cortex (area 8a and frontal eye fields)
in two cases premotor cortex
ML
combination of those from anterior and posterior fields, involved less of extreme frontal pole and frontal eye fields
AL
frontal pole (area 10)
principal sulcus
lateral inferior convexity (areas 12 vl and 45)
lateral orbital cortex (areas 11 and 12 o)
highly specific rostrocaudal topographical frontal temporal connections
suggest separate streams of auditory processing targeting distinct domains of the frontal lobe
more detail:
laminar pattern of labelled cells and axons differed
retrogradely labreled cells most often observed in layer 3, 5 and 6
anterior grade fibers most often as patches in layer 1, 5 and 6 or as columns spanning all layers
agrees with with reports of temporal-prefrontal connections and corticocortical feed-forward and feedback connections
in addition to frontal lobe targets, lateral belt regions also projected topographically to anterior temporal lobe and posterioir parietal regions
Alain_2001
EEG and fMRI
fMRI
EEG
64 electrodes, including standard 10 / 20 placement
Cz reference, online re-referenceing to average reference
S1 - S2 match-to-sample task
S1 differed from S2 in pitch and / or location
pitch: lower, identical, higher ?
location: leftward, same, rightward
important: same stimuli, but different task
results:
fMRI
EEG
two ERPs that distinguished neural activity associated to pitch and location processing
1) between 300 - 500 ms after presentation of S1- greater positivity of waveform over inferior frontotemporal regions during pitch task and greater positivity over centroparietal regions during location task
may reflect online processing and maintenance of S1 in working memory for eventual comparison with S2
2) occurred 300 - 400 ms after S2 was presented and showed similar difference in waveforms as for S1 - preceded the P3b wave at parietal sites
may reflect comparison between representations of S1 and S2
stimuli:
in scanner, free-field 3-D auditory stimulation not possible, therefore a virtual 3-D auditory environment was created