diff --git a/src/modality-specific-files/electroencephalography.md b/src/modality-specific-files/electroencephalography.md
index 46ffce2921..e38f2236ef 100644
--- a/src/modality-specific-files/electroencephalography.md
+++ b/src/modality-specific-files/electroencephalography.md
@@ -113,6 +113,18 @@ A guide for using macros can be found at
 -->
 {{ MACROS___make_sidecar_table("eeg.EEGRecommended") }}
 
+These fields MAY be present:
+
+<!-- This block generates a metadata table.
+These tables are defined in
+  src/schema/rules/sidecars
+The definitions of the fields specified in these tables may be found in
+  src/schema/objects/metadata.yaml
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_sidecar_table("eeg.EEGOptional") }}
+
 #### Hardware information
 
 <!-- This block generates a metadata table.
diff --git a/src/modality-specific-files/magnetoencephalography.md b/src/modality-specific-files/magnetoencephalography.md
index c5aff67dcb..369b86fddf 100644
--- a/src/modality-specific-files/magnetoencephalography.md
+++ b/src/modality-specific-files/magnetoencephalography.md
@@ -135,6 +135,18 @@ A guide for using macros can be found at
 -->
 {{ MACROS___make_sidecar_table("meg.MEGRecommended") }}
 
+These fields MAY be present:
+
+<!-- This block generates a metadata table.
+These tables are defined in
+  src/schema/rules/sidecars
+The definitions of the fields specified in these tables may be found in
+  src/schema/objects/metadata.yaml
+A guide for using macros can be found at
+ https://github.com/bids-standard/bids-specification/blob/master/macros_doc.md
+-->
+{{ MACROS___make_sidecar_table("meg.MEGOptional") }}
+
 #### Hardware information
 
 <!-- This block generates a metadata table.
diff --git a/src/schema/objects/metadata.yaml b/src/schema/objects/metadata.yaml
index d0fa480198..2f8d26d33e 100644
--- a/src/schema/objects/metadata.yaml
+++ b/src/schema/objects/metadata.yaml
@@ -901,7 +901,7 @@ ElectricalStimulationParameters:
   display_name: Electrical Stimulation Parameters
   description: |
     Free form description of stimulation parameters, such as frequency or shape.
-    Specific onsets can be specified in the events.tsv file.
+    Specific onsets can be specified in the `events.tsv` file.
     Specific shapes can be described here in freeform text.
   type: string
 ElectrodeManufacturer:
diff --git a/src/schema/rules/sidecars/eeg.yaml b/src/schema/rules/sidecars/eeg.yaml
index f74da26f7b..7a7252d69b 100644
--- a/src/schema/rules/sidecars/eeg.yaml
+++ b/src/schema/rules/sidecars/eeg.yaml
@@ -43,6 +43,7 @@ EEGInstitutionInformation:
     InstitutionAddress: recommended
     InstitutionalDepartmentName: recommended
 
+# Specific EEG fields MUST be present
 EEGRequired:
   selectors:
     - datatype == "eeg"
@@ -57,6 +58,7 @@ EEGRequired:
     PowerLineFrequency: required
     SoftwareFilters: required
 
+# Specific EEG fields SHOULD be present
 EEGRecommended:
   selectors:
     - datatype == "eeg"
@@ -79,6 +81,15 @@ EEGRecommended:
     HardwareFilters: recommended
     SubjectArtefactDescription: recommended
 
+# Specific EEG fields MAY be present
+EEGOptional:
+  selectors:
+    - datatype == "eeg"
+    - suffix == "eeg"
+  fields:
+    ElectricalStimulation: optional
+    ElectricalStimulationParameters: optional
+
 # General fields
 EEGCoordsystemGeneral:
   selectors:
diff --git a/src/schema/rules/sidecars/meg.yaml b/src/schema/rules/sidecars/meg.yaml
index 0b624e1559..a989d40f9f 100644
--- a/src/schema/rules/sidecars/meg.yaml
+++ b/src/schema/rules/sidecars/meg.yaml
@@ -107,6 +107,15 @@ MEGRecommended:
     AssociatedEmptyRoom: recommended
     HardwareFilters: recommended
 
+# Specific MEG fields MAY be present
+MEGOptional:
+  selectors:
+    - datatype == "meg"
+    - suffix == "meg"
+  fields:
+    ElectricalStimulation: optional
+    ElectricalStimulationParameters: optional
+
 # Specific EEG fields
 # NOTE: I'm not sure if "EEG is present" is enough to indicate simultaneous EEG/MEG.
 MEGwithEEG: